INERIS, Vemeuil Jean Pierre Josien

En Halatte

THE PREVENTION OF ROCKBURSTS IN GARDANNE COLLIERY

This research is based both on numerical modelisation and geophysical measurements. Before mining each new longwall, a numerical modelisation is made to determine the increase of stress created in the areas surrounding the new longwall. Therefore, the smallest distance between the longwall and the existing roadways can be assessed. Permanent seismic monitoring is used to calibrate the numerical modelisation. During the mining Operation geotechnical measurements are carried out in order to verify the results of the numerical modelisation. These measurements concem the convergence of the roof and wall and the expansion in the coal. Bore-testing and electro-magnetic measurements on the coal under stress are also carried out. The efficiency of these methods has been perfected by carrying out systematic prevention plans for each new longwall. This plan was constructed with a rigourous methodology using the füll ränge of geotechnical, geometrical, tectonic and historic data for the concemed area. A quality control procedure provides the means of checking the successfui application ofthe prevention plans and creating a data bank to use in future developments.

I -INTRODUCTION

The Gardanne colliery lies between Aix-en-Provence and Marseiile and is part of the south-east complex ofH.B.C.M. (Subsidiary ofthe Charbonnages de France group). The coal deposit is from fluvio-lacustral origin and was formed some 75 millions years ago. The stratigraphical sequence is mainly composed by limestone (qualified äs hard and brittle) and mudstone. The general geological setting ofthe basin is quite simple. After Gaviglio and al (1988), the structure is overridden by a major thrust sheet overthrusting northward with 25 degrees average dip.Strike-slip, subvertical faulting is present all over the area, with lengths of several hundreds of metres. Most faults have throws less than 2 metres. The stratas dip westward around 15-20 %. At present, the coal is mined from a depth between 1100 m (longwall faces) and 1400 m (development works). Drill-core and vibroseismic profiles show that the maximum depth ofthe seam is about 1450 m.

26eme Conference internationale des Instituts de Recherches sur la Securite dans les Mines, Katowice, 4-8 septembre 1995

Only one seam with a thickness averaging 2,5 m is economically recoverable. This seam is embedded in limestone which forms competent stratas and has a uniaxial compressive strength of up to 150 Mpa. The principal Stresses of the surrounding rocks are measured by the hydraulic fracturing method. These measurements show a strong anisotropy of the principal stress components, characterized by high horizontal tectonic Stresses (between 20 and 40 Mpa) and a sublithostatic vertical stress.In spite of faults, the coalfield is quite regulär. Combined with, in average, good strata conditions, this allows a large scale mechanization. The longwall faces method with caving process is used; the length of span is 220 m; The faces are equipped with plough and hydraulic powered supports. The faces progress between 4 and 8 metres a day per face.

During 1994, the seismic network recorded 125 events ofmagnitude comprised between 2,6 and 3,2. Most of these events are attributed to the goafmg process associated with the longwall mining operations. During the last years, many of these events result in more or less damageable rockbursts (Figure l).

Fig u re 1 :NumberofRockbu rsts

Classified with regard to rockbursts locations and effects at the Gardanne colliery, three main types (figure 2) have been recognized äs: Type l : coal bumps at the ends of the faces, mainly on the old panel side. Type 2 : mainly sudden floor heaves which can reach l m (with a slight ejection of the coal seam), over lengths up to 100 m. They take place either ahead of the face (in tail gate) or behind the face (in main gate) at a distance ranging from50to 150m. Type 3 : coal bumps in unmined , Figure 2 overloaded stiff pillars.

To prevent the rockbursts, two destressing methods are used in Gardanne colliery :

-near the end of the faces, destressing holes (diameter 108 mm, length 10 m) are drilled with an interval, depending of the stress level, comprised between 2 and 3 metres; their progressive generalization (figure 3) since 1991 explains the decrease of coalbursts near the faces.

-before the face winning, the floor of the two gates is slotted (width 0,15 m, depth 0,9 m). This technic is also used around weak pillars in the surrounding of faces. This technic, introduced in 1991, seems efficient against most floor heavages.

II METHODOLOGY FOR CONTROLLING GROUND HEAVE

Rock burst is a complex phenomenon. Its control requires the application of an overall methodology äs indicated on figure 4. This methodology is based upon the feedback of experience (back analysis), in other words the risk analysis is based on analogy with other, previously worked sites. Our efforts in recent years have therefore concentrated on organising the collection of information -in the form of a geotechnical database -with its effective retrieval in the planning stage of a face project.

The methodology leads to a procedure for dealing with the risk of rock burst, a procedure which is applied from the project planning stage through to the completion of each panel. In the planning phase, the risk analysis is based upon: knowledge of the natural state of stress based on measurements using hydraulic fracturing in each district; Simulation of stress modifications due to eariier and planned workings; a geotechnical plan of the future face combining all the geological and geotechnicaldata together with operational Information such äs pressure effects during the driving ofgates. This phase ends with the preparation of a prevention plan jointly by the operators and the specialists who indicate the surveillance and stress relief measures to be taken and their location in space and time. During operations, the procedure primarily includes the controlled introduction of the assessment plan but also: verification of the validity of the risk analysis using remote seismic surveillance; checks on the state of the rock mass and on the efficiency of the preventive measures carried out. Substantial progress in this field should result from the completion of the IMPULS System based upon electromagnetic monitoring of the rock mass developed by VNIMI (Russia).

Following the operational phase, the review stage is essential for completing the "knowledge base" which will enable future sites to be dealt with more effectively.

ffl -PREVENTION SCHEME FOR FACES 02 AND 20

The application of this strategy for controlling rock burst will be explained using an example: the case of faces 02 and 20 in the Arbois district. These faces occupy a decisive position for the future of the workings because they complete the cutting of the principal shaft barrier pilar (Y) and abut on the permanent infrastructure that will serve the westem extension ofthe mine (figure 5).

In order to simulate stress changes due to the workings, Software was needed that would be sufficiently easy to use for studying the different configurations of the working geometry during the project. Programs using finite element methods which can represent the mechanical properties of the different strata, and distinct element methods which explicitly represent discontinuities (faults, etc.) are too involved, especially in three dimensions, for routine use in planning all the workings. For this reason, a boundary element program was selected: SUIT 3D. This has the advantage of taking the horizontal Stresses into account; these are asymmetrical and high in the area prone to rock burst, It uses an empirical model for the behaviour of the caving areas based upon the VNIMI experience.

For the Provence mine, this program was calibrated on the case of a rock burst which affected a pillar to the east of the Y shaft banier pilar. In this area, distinct element modelling was done using the 3DEC (TTASCA) code; where displacements along faults are not too great, the variations in vertical Stresses obtained with 3DEC and SUIT 3D are comparable, which confirms that SUIT 3D is suitable for project planning.

Figure 5 shows the contours of the supplementary Stresses due to simultaneous working of faces 02 and 20 in the final stage of the planned workings. According to the additional stress values, the infrastructure and barrier pülars were fitted with pressure cells and with convergence and expansion cells. The evolution of these measurements were used to determine the positions at which the face workings were actually terminated.

IV -MONITORING OF THE FACES 02 and 20 IV.l-seismic measurements

For 3 years now, every moming, the locations of the events of the day before and a criteria based on the evolution of the seismic energy versus the face advance have been given to themanagement of the mine. This criteria is not always satisfactory. Thanks to the recent improvements of the seismic network, new results give more operationnal indications. The graph of the cumulative energy dissipated by seismic events versus the face advance (figure 6) give us interesting informations :

-during the 500 first metres (until 31/8/94), the evolution is linear. All the seismic energy was dissipated in small tremors (magnitude max 2,81); during this period neither a small rockburst nor a little heavage happens. -during the last 400 metres, the cumulative. energy slightly slowdown; when the energy difference was more than 4 l O 9 J, 15 tremors of magnitude between 2,9 and 3,17 and 7 floor heaves occur.

These floor heaves and this seismic activity are likely linked to the fault which crossed the face during the second period (figure 7). Studies about the focal mechanism are carried out to confirm this interpretation. -The first and second periods are distinguished by different slopes of the lines associated; among the 7300 seismic events recorded, only 2 have a magnitude higher than 2,9; äs for the first period of face 02, no rockburst, even small, happens. Additionnal studies are necessary to determine if the change of slope is linked to the faults which are within 60 m from the tail gate (figure 9); in other cases, in similar configurations, rockburst occur. -just before the end of the face, when the faults crossed the tail gate, the cumulative energy slows slightly and the differential energy increases; this fact is partially at the origin ofthe decision to stop the face.

As we dont know a priori ,with enough precision, the energy level of a face, this kind of criteria, based on the energy deficit, cannot be used during the first 200 metres of face advance. And even after, it is only an indication of the risk of occurrence of high magnitude events.

Magnttude

The distribution of events in function of their magnitude and the b-values (figure 10) distinguish cleariy the second period of the face 02. The number of events recorded (40 per day and per face) allows the processing of these graphs each week for the last month. This kind of criteria, even if it is possible to process it sooner than the energy deficit, must be put in correlation with other indications to be usable.

IV.2-Electro-magnetic measurements

Principles of the measurements When stressed, stratas emit electro-magneüc Signals. The VOLNA apparatus, by mean of a receiver, detects the Signals emitted by the rocks within a radius of 10 metres. Simultaneously, it processes and records the datas. Finally, it indicates the operator a level ofrisk. Successively on 11 levels of energy (Ei), the apparatus counts the number of times (Ni) that each energy level is reached during a space of time. The representation of log(Ni) versus Ei is approximately linear and can be characterized by two parameters; the first one (N), is representative of the average of the eleven values Ni and the second one (B) indicates the slope of the line. The risk increases when N increases and when the absolute value ofB decreases.

To make the apparatus operationnal in the Gardanne colliery conditions, it was first necessary to determine the frequency of the receiver, to find in which energy interval the Signals are correctiy received and to fix the duration of the recording so äs to obtain usable values of Ni. Then, several months of measurements were necessary to find the relation between the measures and the risk level. The level of risk is represented by a number between 0 and 3 (0 and l = no risk ; 2 = «suspect area »; 3 = « a rockburst is possible »).

The measurements are done once a week, in main and tail gate with an interval of 5 metres near the face and 10 metres further. The table 3 indicates the average values for each concemed area. During the first period of the face 02, the electomagnetic measurements indicate that there was no risk in tau gate and that destressing operations were efficient in main gate. Unfortunately, on account of electrical agreement procedures, we have no measurement before the 3 heaves in tail gate. On the 17th of november, in tail gate, the apparatus indicated the risk maximum so the mine management decided to drill again the destressing holes from the face end. After destressing, the measurements were correct again. In main gate, since the beginning of december, the apparatus indicates a high level of risk equally in the distressed and in the non destressed area. In spite of the drilling of new destressing holes (on each side of the gate) and in spite of the floor slotting, 3 slight heaves occur. These facts (and the effect of the face upon some pillars) leaded the mine management to stop the face. This exemple shows that. even if the electro-magnetic measurements are not reliable enough to characterize alone the level of risk. it is possible to use them äs a mean to control the effectiveness ofthe destressing operations.

IV . 3 • MONITORING of PILLARS

The monitoring of the pillars between the two faces is realized by : -The seismic network :

Each month, usually, l to 3 events are located in the neighbourhood of the pillars between the two faces. Their number began to increase during December 94; during January 95, two events are noticeable; one of magnitude 3 but without any damage and one ofmagnitude 1,7 with very slight damages (a coalbump of2 cubic metres!).

The maximum rate of events (6 per month) occured during February and March. -The evolution of the deformations of the pillars : measurement and recording are done each week and transmitted to the mine management Each measurement Station (spotted l to 5 on figure 11) has a convergence device, two ribside extensometers and a pressure cell. The first evolutions (convergences of respectively 2 and l mm) were detected in January (stations l and 2) just after the event of magnitude 3. The face 20 was within 300 metres and the face 02 at about 500m of the concerned pillar. The second evolutions, more important (12 mm of convergence, 41 mm of expansion of a ribside) appeared in February (stations l, 2, 4 and 5). The face 20 was stopped and the face 02 was between 350 m and 400 m (depending of the pillar concemed). So, we can notice that these results (seismic events and deformation measurements) are in accordance with those of the numerical modelling which indicates that:

-the face 20 has little influence on the pillars area. -the influence of the face 20 will begin only when the face will be at a distance of less man 350 m.

V -CQNCLUSIQNS

In recent years the seam mined in the Provence coalfield became much more susceptible to rock burst because of depth and unfavourable tectonics. However the number of rock burst incidents was reduced by introducing a control methodology that was highiy effective in our working conditions.

The main features of this methodology are:

an overall procedure defming the steps to be taken, from the stage of planning the workings. This procedure which is based on a quality approach, is being reviewed äs operations proceeded in the light of site monitoring data.ê xtensive use of stress relief techniques, made economically viable by mechanisation of stress relief hole drilling and floor slotting roadways; improvements in the methods used for prediction (computation Software) and monitoring (seismic and electromagnetic techniques) in Order to increase their performance and include them in routine operational practice; dose co-operation between the operators, the specialized departments of the ndne and the research insdtute including international co-operation in the development of new technical facilities.

Figure

  Figure 3: e volution ofthe utilization of destressing methods

  figure 4 : controlling dynamic phenomena methodology for action

  figure 5 : plan view of face 02 and face 20 contours of supplementary vertical stresses

Figure

  Figure 6 : Cumulative energy versus face advance ofTO2 Arboisnord

Figure 9 :

 9 Figure 9 : T20 Arbois sud

Figure

  Figure 11 -pillars

Table 3

 3

	: T02 ARBOIS NORD -electro-magnetic measurements
	Date		Tail gate			Main gate
	Destresse	Betöre	Observation	Destresse	Before the	Observation
	d area		the	s	d area	destressed	s
			destresse			area
			darea
	21/04/1994	1	1		1,7	2
	20/05/1994	1	1		1	2,4
				3 heavages
	17/11/1994	2,7	3		1,6	1,6
	21/11/1994	1,2	2,3
	01/12/1994	2,2	2,8		2,8	2,8
	19/12/1994	1,7	2		2,2	2,4
	06/01/1995	1,5	2,2		2,7	2,8
	13/01/1995	2	1,9		2,4	2,4	heavage
							heavage
	03/02/1995				2,6	3
	08/02/1995	2,2	2,3		2,8	2,9
	13/02/1995	2	2,2		2,8	2,8	heavage
	21/02/1995	2,2	2,6		2,2	2,8


Gerard Rose

A NEW METHANOMETER WITHOUT ANY CALIBRATION

In this paper, we explain how a new technique of heating a catalydc wire at a constant temperature, and a new method of measurement using two temperature levels, have allowed the development of a very perfonning multi-purpose methanometer, with no need for calibration during throughout the life of the sensor.

The main advantages are:

-improved reliability of the sensor since no compensating element is used, -accurate measurement of the volumic rado up to the lower explosive level, äs required by the Standards, even without of a compensating element, -no zero or sensitivity drift, and hence no calibration required, -low power consumption : heating the wire needs a l volt battery and takes only 0,08 ampere, giving long battery life, -no uncertainty of the reading about the concentration (above or below stoichiometry).

26eme Conference internationale des Instituts de Recherches sur la Securite dans les Mines, Katowice, 4-8 septembre 1995

INTRODIJCTION

State of the art

The sensor most commonly used for detecdng firedamp (methane) and measuring its concentradon in mines is the catalydc sensor, which costs less than an infra-red detector.

The convendonal catalydc sensor has two component parts -a detecdng element and a compensadng element -enclosed in a flameproof reacdon chamber. The detector is a filament encased in a pellet of composite material, made up of alumina mixed with powdered metal (palladium or pladnum) which acts äs an oxidadon catalyst.

The compensadng element is idendcal with the detecdng element, but its alumina pellet contains no catalyst. The two filaments are connected up in a Wheatstone bridge circuit (figure l); a steady current flows through the filaments and raises die temperature of die pellets to about 600°C. In die presence of mediane, die heat given off by oxidadon of die mediane in die detector pellet increases the filament temperature, causing a rise in its electrical resistance proportional to the temperature [l]. The bridge is dien no longer balanced, a situadon which die medianometer displays äs a percentage of mediane by volume.

Changes in die temperature and moisture content of die gaseous mixture influence die temperature of bodi filaments in die same way. Their resistances dius change by die same amount and die bridge remains in balance. The new catalytic sensor developed by INERIS is of simpler design in that it no longer has a compensadng element, the result being lower power consumption and better reliability. To make up for the absence of a compensating element, a special technique is used for the electrical conditioning of the detector element, which cancels out the effects of changes in environmental parameters and improves the performance of the sensor and of the methanometer:

there is less drift in the performance of the meter, obviating calibration and on-site maintenance, uncertainty is reduced, power consumption is much less.

The detector element is an extra-pme platinum wire.

2mm *| dia = 80 um i 0,3mm
Plarinum detector filament

CONDTTTONTNG TECHNTOTJE

The filament is used intermittently. It is heated for the minimum period of time needed to make a measurement, then switched off for äs long äs possible according to the desired response time for the particular application (this period of time can be programmed by the user) (figure 2). If t^ is the heating period, t^ff the time during which the filament is switched off and 1^ mean ^e mean heating current, then the mean current Imean ta ^en from the battery is equal to [2]:

Di mean

OmAJ

; th: toff figure n°2: discontinuous heating th I mean = Ih mean x [2] m + toff
For an 80 pm filament: 1^ ^g^ = l A; t^ = 0.4 s iftofc==5seconds:

I^=lxj^=0,08A

For a given response time, the power consumpdon is four times less than that of a condnuously heated catalytic pellet and, having regard to the power taken by the compensadng element, eight times less than that ofthe convendonal sensor.

The headng of the filament incorporates two holding phases, at 900°C and 1000°C respecrively (figure 3). The filament response is measured at these two temperatures, and the concentradon then caiculated by the methanometer using the formula:

conc. in % by vol. = [Resp(1000°C) -Resp(900°C)] x K [4]
The temperatures indicated are those at the centre of the filament.

Di T-amh-

• : th toff figure n°3 : two levels oftemperature

Heatins at constant resistance and temperature: filament response

The filament operating temperature is maintained at 900°C and 1000°C by a control circuit which indirectiy determines the temperature of the filament by measuring its hot resistance, and modifying the heating current to keep this resistance constant (figure 4).

When methane is present, the control circuit reduces 1^ in order to compensate for the heat generated by the reaction.

The change in 1^ which is proportional to the methane concentration constitutes the filament's response to this gas.

Note

It is important to control the filament temperature to ensure that it does not exceed 1000°C, for example when the methane oxidation reaction takes place; above this temperature, there is substantial evaporation of the pladnum. Unless this precaution is taken, filament wear would be very rapid and its lifedme would depend on the quandries of methane it encounters. With constant temperature Operation, filament wear depends only on the number ofintenogations and can thus be modelled. To caiculate the response _U^(T), the methanometer needs the value ofUf(T) in clean air [Uf)()CD] in its memory.

The methanometer automadcally measures and Stores the value of UfQ(T) when it is calibrated following the installadon of a new filament. The air used should be free of any combusdble gas but its temperature and reladve humidity arc unimportant.

Resp(1000°C) = Ufo(1000°C) -Uf(1000°C) Resp( 900°C) = UfQ(900°C) -Uf(900°C)
Measurement sequence fßpure 5) [5] [6] filament heated to 900°C 11: measurementofUf (900°C) t^ headngtolOOO°C (3: measurement ofUf (1000°C) 14: headng tumed off -caiculadon and display of concentration using the formulas

Uf(1000°C)---- Uf(900 < 'C)• • --• l-m oooliioi o-l- r "•
[5][6][7] C(% by vol) = [Resp( 1000°C) -Resp(900°C)] x K [7]

Compensation for environmental factors

The differential measurement reduces the effects of environmental parameters. Figure 6 shows the response of the filament to diese parameters for different heating temperatures.

Resp.rAUf) 1 '50 mV '

It can be seen that by subtracdng the response at 1000°C from that at 900°C, the measurement for 1% by volume of CH4 is 20 mV (25-5), for a substantial change in ambient temperature it is zero (17-7), and for a substandal change in relative humidity it is -4 mV (-11 + 7), or the equivalent of 0.20% by volume of CH4; an error persists, but this is nevertheless within the tolerances ofEuropean Standard 50 055 on methanometers covering the ränge 0-5% by volume. If all these parameters change at the same time, the response at T is the algebraic sum of the responses to each of the parameters taken separately.

The following table gives the responses and the measurement for the different parameters: CH4, Tg^o, relative humidity, and filament position, in the case where calibration was done using clean air in a room at 20°C with 50% RH.

\ / ^\ 2 l Rf(T) = cst = RO(1+KT); T-f(Ih(T)) [11]| ^ ^ j =f(%CH4) l = f(Tamb ; hum.) |
RO thus increases with wear [10], with the result -owing to the principle of constant resistance hearing -that there is a negadve drift in the heating currents and in the response at900 0 CandlOOO O C[ll].

Note: The measurements are thereby increased by an amount which-rises with the number of interrogations. This quandty can be measured directiy in clean air, hence it is known äs the "zero drift". Figure 8 shows the drift in responses at 900°C and 1000°C, and the drift in the measurement which is the difference of the other two. The drift in the measurement is small and we have verified, by tests on a number of filaments, that it was reproducible. Thus the methanometer can automatically correct for this drift according to the number of interrogations accumulated since the new filament was fitted. Owing to the principle of constant rcsistance heating, the temperature of the filament falls when RQ increases, i.e., äs the filament wears. The result is a negative drift in the responses to methane (figure 9). However the measurement, which is the difference between the two responses, falls less quickly than either ofthem (figure 10). Just äs for the -zsto drift, the reprodudbility of this drift means that the methanometer can make an automadc correcdon according to the number of interrogations made since the filament was installed.

Less uncertaintv

Methane is a better conductor of heat than air, and its conductivity increases with temperature (figure 11). This partly explains why, for a concentration greater than stoichiometric, the response at 900°C becomes greater than that at 1000°C, leading to a highiy negadve measurement (figure 12).

thennal conductivity, |Resp. 1000.900 1000 .900°C filament life: > 8 million intenogadons or 15 months for an interval of5 seconds (30 months for an interval of 30 seconds); no maintenance: the methanometer requires no maintenance throughout the life of the sensor. The maximum measurement error would then be ± 0.25% by vol. of CT^; power consumpüon: 0.08 A for a 5-second interrogadon interval; 0.04 A for an interval of 10 seconds; battery life: 40 hours for a interrogadon interval of 5 s with a 4 Ah battery at 1.25 V.

PROSPEKTS

Together with another French laboratory (LETI), INERIS is compledng the development of a catalydc microfilament characterised by very low power consumpdon: the duradon of headng is 0.08 s and the headng current is 0.15 A. Acconüng to [2], the current taken by the methanometer is only 2 mA for an interval of 5 s and l mA for an interval of 10 s. In these condidons the battery life is several months.

  figure n°l: Wheatstone bridge

  figure n 0 4: heating device

  figure n°7: temperatures along the filament

  figure n°8 : zero drift

  figure n°9: drift of temperatures figure n°10: drift of sensiüvity


Zbigniew Pokryszka

Christian Tauziede

Philippe Cassini

DEVELOPMENT AND VALIDATION OF A METHOD FOR MEASURING BIOGAS EMISSIONS USING A DYNAMIC CHAMBER

Development and validation of a method for measuring biogas emissions using a dynamic chamber

Zbigniew Pokryszka, Christian Tauziède, Philippe Cassini

INTRODUCTION

The landfilling of waste is likely to put into the environment polluting or malodorous substances, a large part of which is released in the form of gas. Among the different types of landfills, it is MSW that emits the most intense gas releases.

A mixture of gases (known as biogas) is produced from organic waste, and consists mainly of methane, carbon dioxide and other gases in much lesser quantities.

The consequences of biogas release are extremely diverse, but the following are the major consequences recognized at the present time (see Figure 1):

The risk of explosible mixtures which can migrate to urban areas Hundreds of accidents (i.e. explosions) or incidents arising from migrating biogas have occurred and been reported [START_REF] Rees | The Fate of Organic Carbon Compounds in the Landfill Disposal of Organic Matter[END_REF][START_REF] Bouwman | Landfill gas -a potential environmental hazard[END_REF][START_REF] Gendebien | Landfill gas. From environment to energy[END_REF]. Waste dumps (including MSW landfills) often release toxic or malodorous gases which can affect urban areas [START_REF] Gendebien | Landfill gas. From environment to energy[END_REF].

Greenhouse Effect

The ratio of the landfill released methane to the global released methane (one of the main causes of the Greenhouse Effect) ranks, according to one or another estimation, from 5% to 25% in France and at approximately 20% throughout the world.

Having regard to the consequences described above and the potential dangers arising from biogas output, it is essential to have a system and a procedure enabling gas release to be defined and quantified, for the following purposes:

-to meet international obligations in respect of the inventory and prevention of gas causing the greenhouse effect;

-to ascertain by on-site tests the best suited treatment and landfilling methods in order to reduce gas emission;

-to define the decisions required in order to implement the techniques necessary to reduce and prevent gas emission;

-to design a system for assessing the effectiveness of the above techniques;

-lastly, to detect and evaluate risks arising from gaseous emissions such as, for example, the drift of pollutants and flammable gases.

Thus the aim of the research carried out by INERIS, under the project financed by the Ministry of the Environment, was to develop a simple and reliable way of measuring the emission of gas from the surface of a landfill (Pokryszka, 1993).

SELECTION OF MEASURING METHOD

The available literature contains a number of methods designed to measure surface gas flow rates, and indeed has been reviewed in order to weigh up their various advantages and disadvantages. Following this, it was decided to orient the research in the direction of localized gas flow measurement using a dynamic chamber.

The usefulness of this type of technique is twofold: first, it allows direct measurement not dependent on hypotheses in respect of the emission and dispersion of gas into the atmosphere; secondly, it can be carried out in a wider range of gas concentration, which greatly facilitates the operation. This method and its application are often to be found in the relevant literature [START_REF] Denmead | Chamber systems for measuring nitrous oxide emissions from soils in the field[END_REF][START_REF] Jury | Analysis of chamber methods used for measuring nitrous oxide production in the field[END_REF][START_REF] Christensen | Nitrous oxide emission from the soil surface : continuous measurement by gas chromatography[END_REF][START_REF] Hunsted | An open chamber technique for determination of methane emission from stored livestock manure[END_REF].

The chief advantages emphasized by the authors are the simplicity of the system, the ability to detect minimal gas flow leaks, reliability of measurements and the fact that the system can be used in adverse meteorological or topographical conditions. The main drawback is modification of the gas flow in the field and of gas exchange at the earth-air interface [START_REF] Mosier | Gas flux measurement techniques with special reference to techniques suitable for measurements over large ecologically uniform areas[END_REF].

The approach adopted in the end for future development was a flux dynamic chamber.

WORKING PRINCIPLE OF THE FLUX CHAMBER

The method of measuring biogas emissions by using a dynamic chamber is a direct method and consists (see Figure 2) of the following:

-Covering an area as hermetically as possible, without altering the environment. The shape of the area covered should be elongated and the height of the enclosed volume should be minimal.

-Getting a sweep gas flow (inert gas) in the measuring chamber by injection at one end "e" (entry).

The sweeping flow rate should be distinctly higher than the rate of gas release in the covered area.

-Passive collection and measurement of the sweep gas/biogas mixture at the other end "s" (exit) of the chamber.

-Follow-up of the concentration of biogas constituents in the collected gas. On the basis of the parameters measured and given an analytical model, the flow of biogas from the chamber and thus the flow rate emitted by the covered area can be determined. C bs (i) Concentration of biogas constituent i in the gas coming out of the chamber, (adimensional) q b (i) Flow rate of biogas constituent i per square metre of the surface area S, (Nml/min/m 2 )

Symbols

S

Choice of Analytical Model

Figure 2 shows the gas flows into and out of the system. The flow of biogas coming out of the chamber is calculated using the formula below by measuring the value Q s and the concentration of the biogas constituents:

Q Q C (i) bs s bs i = 1 n (1)
The Q bs value determined by Formula 1 above represents only a part of the biogas released from the surface area S. This part equals the total biogas emission Q b from the surface S, reduced by the leak rate, as follows:

Q < Q bs b
(2)

Leaks result from two causes:

-The presence of the chamber affects gas flow in the ground and gas exchange with the free air.

Part of the gas, usually emitted by the surface area S, does not enter the chamber but migrates laterally (Type 1 leaks, flow rate Q bf1 ).

-The system is not completely leak proof, so some of the gas coming into the chamber escapes in the same way as the sweep gas (Type 2 leaks, flow rate Q bf2 ).

To express the mass conservation equation in respect of biogas, we obtain the following:

Q = Q + Q + Q b bs bf1 bf2 (3)
Unfortunately, this equation does not enable the actual unaffected biogas flow rate Q b to be determined as the leak rate is unknown and difficult (not to say impossible) to measure or evaluate by a simple method.

If the aim is to get an analytical model and a measuring procedure relatively simple, a number of simplifying hypotheses need to be applied. Thus on the supposition that the total leak flow rate of biogas is approximately proportional to the Q b biogas emitted, and remains constant for measurements performed under conditions that remain identical, the biogas recovery rate can be expressed as follows:

K = Q Q b bs b (4)
From ( 1) and ( 4) we obtain the following:

Q b = Q K C (i) s b bs i = 1 n (5)
If we reduce this to surface S, we obtain the flow rate of biogas per square metre:

q = Q S b b (6)
Thus:

q = Q K S C (i) b s b bs i = 1 n (7)
If one takes into account only one of the constituents, its emission flow rate per square metre is given by the following formula:

q (i) = Q K S C (i) b s b bs (8)
So we can determine the required Q b value on the basis of Q s and the C bs (i) concentrations, provided we know the recovery rate of the biogas K b .

The K b value, i.e the relationship between the measured biogas collected flow rate and the actual emitted flow rate results from both the way in which the measuring equipment influences the biogas emission and in a certain way the tightness of the measuring chamber. So it can vary according to the operating parameters of the method (chamber construction, flow rate and speed of the sweep gas, and so on) and the "natural" conditions (type of ground, permeability, biogas emission flow rate, etc.)

DEVELOPMENT OF METHODOLOGY

As indicated above, installing a chamber affects gas exchanges between the ground and the air, which by their very nature are characterized by very low pressure gradients. This situation can give rise to measurements that are not entirely accurate. The degree of inaccuracy is initially unknown.

As a result, it was necessary first of all to validate the method designed in the laboratory and in situ. The chief purpose of this was to define the corrective factor(s) to apply in order to compensate for the effect of measuring on the measured value.

Thus in terms of the methodology applied, work was divided into three phases, as follows:

-constructing the chamber and defining the operational parameters; -adjustment and validation of the method on a laboratory test bench; -lastly, final adjustment by in situ measurements.

CONSTRUCTION OF THE CHAMBER

The initial phase consisted of constructing the chamber and determining the operational parameters (see Figure 3). Thus the measuring chamber is made up of a plastic film held at approximately 10 cm from the surface of the ground by rigid supports. It is in the shape of a rectangle 5 metres long and 1 metre wide. The impermeability of the chamber on the ground is ensured by a strip of moist sand or clay.

Injection of the sweep gas is done by a feed system consisting of a perforated pipe designed such that the gas is distributed evenly on the whole width of one small side of the chamber. When it leaves the chamber, the gas is collected by two 40-mm tubes which converge into a single pipe.

The flow rate of the sweep gas/biogas mixture coming out of the chamber is determined on the basis of the speed measured by a hot-wire anemometer in the outlet pipe. During validation tests, this flow rate was measured very accurately using helium tracing. Samples of gas coming from the chamber required in order to analyze its composition are taken from an opening located at the end of the outlet pipe, using a suction pump.

VALIDATION OF MEASURING METHOD

Design of Test Bench

In order to test the method, a test bench ensuring a well-regulated gas emission was designed and built such as to represent emission under actual conditions. It consists of a layer of sand under which a mixture of methane and carbon dioxide flows out (see Figure 4 Dimensions are as follows: length 6 metres, width 1.8 metres, height approximately 0.2 metres. The biogas flow is regulated by a mass flowmeter and distributed under the test bench by numerous uniformly perforated hoses. Near the test bench there is a fan designed to create locally draughts simulating normal wind.

Parameters

During tests, we varied the following parameters: Ground permeability, including water and compaction. Three types of ground were examined: highly permeable (dry sand); moderately permeable (moist sand); and fairly impermeable (compacted and water-saturated sand).

Q v sweep
Side wind: measures were taken on a wind ranging from 0 to 4.5 m/s.

Results

Testing the method on the test bench confirmed that the method used affects gas emission regardless of the precautions taken. The ratio between the actual emission and the emission observed in the chamber can in extreme cases reach values of 3 to 4.

The rate of biogas recovery K b varied within a range of 0.3 to 0.95 depending on measuring conditions. Experiments have shown that this parameter required in order to determine the biogas emission rate depends simultaneously on the sweep gas rate Q v and ground permeability. Whilst the Q v value is constant and known when measurements are in progress, the permeability of a landfill cover is unknown, and technically hard to determine. Additionally, the permeability value can vary considerably over the surface examined. Thus it is beforehand impossible to establish a relationship enabling the determination of the K b on the basis of the Q v value and ground permeability.

Numerous complementary experiments conducted on the test bench have enabled us to resolve this problem.

First, experiments confirmed the hypotheses established when the analytical model was defined. More particularly, they showed that biogas leaks were approximately proportional to the biogas emission rate Q b and constant (relatively) for measurements performed under identical conditions (see Figure 5). Secondly, we were able to identify an auxiliary parameter: the recovery rate of sweep gas K v , defined as follows:

K = Q Q v vs v (9)
By definition, the K v value is constant for a given measurement configuration. Since Q bs << Q vs , the value can be determined on a practical basis by the following formula:

K = Q Q v s v (10)
Thirdly, it has been shown that K v depends, rather like K b , on the sweep gas flow rate Q v and ground permeability. This justified looking into the possibility of a statistical relationship between values K b and K v . And in fact the existence of this relationship was very clearly confirmed by a non-linear regression calculation on the basis of some 90 measuring points. One of the best correlations (r 2 = 0.98) was obtained by the function shown in Figure 6. A relatively low dispersion of the values around the regression curve enabled us to establish prediction limits not far from this curve. The confidence level retained in order to establish prediction limits is (1 -) = 95%.

The relation found can be used to determine the unknown value of K b , which is required for working out the biogas emission rate (see formulae 7 and 8 above) on the basis of the K v value, which can be measured. This means that it is not necessary to know the dump cover permeability value. The uncertainty margin of a value obtained for K b is defined by the limits of prediction. This solution has been confirmed and validated by several reliability and repeatability tests carried out in very varied configurations (cf. § 6.2). Figure 7 shows a comparison between actual methane emission rate and collected methane measured during different reliability tests. The dispersion of values around an ideal solution is very low. It never exceeds a theoretical maximum error limit estimated at 15%. This proves the reliability of the method and the relevance of the analytical model used. The repeated tests carried out in the same conditions of ground, biogas emission and injection of sweep gas made it possible to examine the repeatability of the measures obtained by the method. The dispersion coefficients of the results obtained under similar conditions were of the order of 3%, thus the method does, under laboratory conditions, ensure a very good measurement repeatability rate.

The numerous tests conducted have also made it possible to determine the optimum operating parameters in respect of the conditions governing the method used. For example, they showed that, thanks to a relatively large sweep gas flow, the method gives appropriate results up to a wind speed of 4.5m/s.

VALIDATION OF THE METHOD IN SITU

Landfill Characteristics

Measures were taken on a specific MSW landfill located in a former clay quarry covering an area of some 3 hectares. The waste (basically MSW) was deposited between 1978 and 1990 to a depth of 4 to 8 metres. Over the entire area, the refuse was covered by a layer of sandy soil well compacted in places. The thickness of the coverage goes from 0.8 to 2 metres. The landfill is not equipped with a biogas drainage system.

Measuring Points and Tests Carried Out

Tests initially involved an area of 125m 2 . Measuring points were spaced regularly over the area at a grid of 25 x 25 metres (Figure 8). One of the main part of experiments was to examine in situ operational relationships and parameters of the method created in virtual laboratory conditions, thus reliability and repeatability tests were carried out.

Results of Validation of In Situ Method

To confirm the validity of the analytical model in situ, a reliability test was carried out. This consisted of determining the emission of methane at the same point a number of times, always applying different working parameters.

For each chamber site, four sweep gas flow rates were examined (40, 60, 80 and approximately 100 Nl/min) and 3 to 4 measurements were taken for each one, at the following points: C3, C5 and D5 (see Figure 8). It should be noted that these points presented very different methane emission levels (respectively in the order of 3, 10 and 100 Nml/min/m 2 ). Similarly, the recovery rate of sweep gas measured at these points varied greatly (respectively, in the order of 0.7, 0.5 and 0.9).

Measurement results are shown in Figure 9, together with the methane flow density values observed at given points and in relation to the working parameters examined. These results show that whatever the level of the above values (within the limits laid down for a normal operation), use of the method will always produce the same methane flow density value at any given point. This proves that the analytical model created in the laboratory can be perfectly well applied in the field.

Validation of the method was complemented by a repeatability test, which consisted of repeating a measurement a number of times at the same point (thus in the same ground conditions) and at the same sweep gas flow rate. In order to examine the method in very different configurations, the sweep gas flow rate was modified from one test to another (20.4 to 102 Nl/min). Similarly, the chamber sites selected for test purposes were caracterized by very different biogas emission values (methane flow 0.03 to 125 Nml/min/m 2 ).

A dozen or so tests of this nature were carried out. These showed (Figure 10) relatively low variability in respect of the results, irrespective of the measuring conditions. Deviations from mean values were less than 8%, thus comparable to those established in laboratory tests. The method ensures good measurement repeatability which is quite sufficient in field conditions. [START_REF] Lifshits | Spatial heterogeneity of gas generation in landfill sites[END_REF]. A bar graph of the spatial distribution of the methane flow values measured is shown in Figure 11.

In situ experimental results have also made it possible to make an initial attempt to assess the overall emission factors on the basis of localized measurements. For this purpose, we used a special geostatistic method -kriging.

The main advantage of this method is that it can be used to map the flow density (Figures 8 and12) over the surface area examined. The average methane flow was evaluated at 11 Nml/min/m 2 , giving a volume of CH 4 released of about 160 Nm 3 per day and per hectare of landfill area. This initial test can be seen as completely positive. But research is still needed in order to define the criteria of selection and the application areas of the different statistical methods as well as the practical means of implementing them.

CONCLUSIONS

One of the approaches used to measure gas surface flow often quoted in the relevant literature is the dynamic flux chamber. The principles involved were tested on a test bench in a first stage.

Tests showed that the measuring equipment affected significantly the emission of biogas to the free air. Consequently, the biogas flow rate measured on exit from the chamber was less than the value that might have been emitted from the surface area covered if there had been no chamber.

The ratio between the actual unaffected emission flow rate and the measured value can in certain cases be quite high (3 or even 4).

In order to define the corrective factors required to compensate for the effect of the measuring on the measured flow, several simulations were effected on a test bench designed to be able to adjust and control the biogas flow. This validation of the method in the laboratory was required in order to define the analytical model whereby it would be possible to calculate the quantity emitted by the covered surface area once known the flow rate of biogas released from the chamber.

The pertinence of the measuring method concept as well as the analytical model issued from the laboratory test have been confirmed by a number of other tests conducted under actual conditions of methane emissions from a MSW landfill. This experiments carried out in situ also confirmed the extremely high spatial heterogeneity of methane emission (ratio 1 to 10 4 ).

The work carried out has therefore produced a tried and proven method of measuring local flow densities of surface methane emissions. The method could in principle be applied in order to measure emissions of other gases produced from the surface, whatever the nature of the ground and the characteristics of the soil.

The studies carried out have also shown the possibility of determining the overall flow from a given site on the basis of local data, using a geostatistic method. That said, a more accurate methodology in respect of this approach remains to be defined.

The foregoing considerations do indicate the main lines of the work to be done in order to establish finally a reliable method of quantification appropriate to the nature of the phenomenon which is as complex as the gaseous emission rates from the areas considered are low.

Figure 1 .

 1 Figure 1. Some forms of potential impact of biogas emissions from landfill

Figure 2 .

 2 Figure 2. Principe of biogas flow measurement by means of the dynamic flux chamber

Figure 3 .

 3 Figure 3. INERIS dynamic flux chamber diagram

Figure 4 .

 4 Figure 4. Diagram of test bench for chamber validation

  gas flow rate: 10.2 Nl/min to 91.8 Nl/min by increments of 10.2 Nl/min Biogas emission: 4 surface flow values -71, 7.1, 0.71 and 0.071 Nml/min/m 2

Figure 5 .

 5 Figure 5. Relationship between ratio K b and methane flux

Figure 7 .

 7 Figure 7. Laboratory results of method reliability test

Figure 8 .

 8 Figure 8. Position of measuring points on the examinated landfill

Figure 9 .

 9 Figure 9. Results of in situ validation of the method

Figure 10 .Figure 11 .

 1011 Figure 10. Results of in situ repeatability test

Figure 12 .

 12 Figure 12. Mapping of methane emission obtained by kriging

ACKNOWLEDGEMENTS

The design and development of a method for measuring biogas emissions are the result of work performed by a whole team of INERIS engineers and technicians. We owe our thanks to the persons who have actively contributed to this study, in particular R. Geveart, J. Havard, M. Hugonie, A. Jodart and P. Jouglet.


D Savanne

P Cassini

Z Pokryszka

C Tauziede

A Tregoures

P Berne

J C Sabroux

P Cellier

P Laville

A COMPARISON OF METHODS FOR ESTIMATING METHANE EMISSIONS FROM MSW LANDFILLS

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

This study was fünded and co-ordinated by the French Agence de l'Environnement et de la Maitrise de l'Energie (Ademe) in the framework of the French research programme on the evolution of the climate and the atmosphere, with the specific aim of estimating the contribution to the greenhouse effect due to methane emitted by municipal solid waste landfills. The objective of the study was to assess and compare different methods for evaluating methane flux densities, with respect to the qualification of the methods in metrological terms, äs well äs their potential for practical implementation at landfill sites. This preliminary step, preceding the execution of direct measurements at seiected sites, will enable researchers later on to validate existing emission modeis and establish by extrapolation an inventory of methane emissions covering all municipal solid waste landfills in France.

EQUIPMENT AND METHODS

Five methods were tested, in two sets of comparisons. Two localised methods were tested: accumulation chambers developed by the Institut National de l'Environnement et des Risques (INERIS) and by the Institut de Protection et de Sürete Nucleaire (IPSN). Three atmospheric methods were tested: a mass balance technique and eddy correlation developed by the Institut National de la Recherche Agronomique (INRA) and a tracer-gas technique developed by IPSN. These methods were tested using two regulated-emissions devices installed by INERIS: a laboratory test-bed for the accumulation chamber methods, and an outdoors regulated-emissions site for the atmospheric methods.

Accumulation Chamber Methods

The INERIS method uses an extemal-recirculatioD chamber covering an area ofO.25 m 2 and with an enclosed volume of 30 litres (l). The intemal atmosphere is renewed using an extemal pump with a flow rate on the order of 10 Vminute. The rate of methane enrichment of the recirculated mixture is monitored, and used to deduce the local methane flux of the covered surface. The methane flux derived outside the chamber is analysed using classical laboratory flame-ionisation chromatography. The chamber was validated beforehand in laboratory tests to ascertain the corrective factors to be applied to adjust for the influence of the measurement on the measured flux.

5th International Landfill Symposium, Sardinia'95, S.Margherita di Pula, 2-6 octobre 1995, vol.ni, p. 475-479

The IPSN method uses a cylindrical accumulation chamber which also serves äs the measurement chamber (2). It covers an area ofO.06 m 2 and has a usable volume of 19 litres. A fan placed inside the chamber ensures evenly-distributed filling throughout the accumulation phase. The chamber is equipped with instrumentation ensuring continual measurement of methane concentration, differential pressure between the interior and the exterior of the chamber, and temperature inside the chamber. The sensor is a semiconductor (TGS doped SnC>2, Figaro Engineering Inc., in an atmosphere desiccated by silica gel).

These two chambers were compared using a test-bed allowing regulated biogas emissions, built by INERIS. The bench consists of a Im x 2m parallelogram-shaped bed of wet sand, roughiy 30cm deep; a mixture of methane, carbon dioxide and water vapour is injected into the bottom ofthe bed under controlled conditions. The methane and carbon dioxide fluxes are regulated by mass flowmeters and distributed in the lower part of the bed by numerous pinhole-perforated tubes. The sand used in the bed and the emitted gas are heated to a temperature between 15 and 50°C by a heating pad placed in the lower part. On one side a fan is used to create air movements above the sand bed that simulate a wind of steady speed and direction. The CI-L^CO; + CI-L) mole ratio is maintamed at a constant value equal to 60%. Methane fliix densities ranging from 0. l to 200 N ml / m 2 / minute can be obtained with this set-up. Six tests with different flux densities between 0.1 to 200 N ml / m 2 / minute. For two ofthe tests, d2w and d7w, a steady wind blowing at 4M/s was sünulated.

Estimation of global flux on the basis of local measurements was not addressed in the framework ofthis comparison using these two non-integrating methods.

Atmospheric Methods

The eddy correlation method (INRA) relies on the principle that the flux density of a compound passing over a horizontal surface at a given time and place can be caiculated äs the product of the vertical wind speed and the concentration of the compound in question (3). This method requires measurement of the vertical wind speed, and of the compound concentration at the same place and moment in time with a frequency of at least 10 Hz. The experimental System is essentially composed of a three-dimensional sonic anemometer (Solent model, Gill) that measures wind components in an orthogonal System and air temperature at 20 Hz, and an adjustable laser diode spectrometer (Aerodyne Research Ltd.)

The mass balance method (INRA) relies on the principle that for a finite surface area, no matter what its characteristics, the flux emitted between the surface edge and the point of measurement is equal to the horizontal flow ofthe compound in question, integrated over the entire height of the boundary layer extending above the surface in question (3). The methane flux is estimated using measurement of wind speeds and methane concentrations at five heights in the lower atmosphere. Wind speed is measured using cupel anemometers (Cimel, Paris). Average methane concentrations are measured afterwards from air samples pumped into Teflon bags placed in rigid Containers. All measurements and air sampling controls were carried out using a central data recording Station (model CR10, Campbell Scientific Ltd.)

The tracer gas method (IPSN) consists in caiculating the methane flux by measuring an atmospheric transfer coefficient (K) obtained using a tracer gas. Between an effluent source and a given point, K is the ratio between the integrated concentration of effluent at this point and the mass of effluent released (4). The method used consists in determining K by emission of a tracer gas under conditions that are äs dose äs possible to those of methane emission, and in measuring simultaneously at the same point the concentrations of the tracer gas and of methane. A constant mass flow, a known quantity, of the tracer gas sulphur hexafluoride SF$ was injected into the methane emission network set up by INERIS. Sampling was done using independent gas sampling devices located at ground level around the site: most ofthe devices were placed downwind at about 4 metres from the last injection line, and one upwind of the site to determine the initial methane concentration. The tracer gas and methane concentration measurements were made at the site using two gas chromatography colurnns equipped respectively with a flame-ionisation detector for CH4 and an electron-capture detector for SFe.

For comparison of these three methods, an even, practically flat plot of ground with no background methane emissions from the soil was found in Etouy, in tbe Oise department norm of Paris. The site was equipped with two sets of twenty 50-meter-long flexible tubes, arranged in parallel with a distance of 5 meters between each tube. The tubes were perforated by very thin metal pipes also 5 metres apart. Each tube was connected to a double central spine that ran the width of the plot along a median line. This double central spine emerged from a segment of single conduit through which all the flow passed. The gas emitted was a mixture of methane, nitrogen äs vector gas and sulphur hexafluoride, in varying proportions.

The emitted flow densities varied between 0.04 and 10.45 NmL^m^min). A test repeating one density has already been carried out in order to ascertain the reproducibility ofthe methods. The eddy correlation method systematically underestimated methane flux density by a factor of 1.5 to 3. This disappointing result has been attributed to a too-smaU test field and to the discrete level of methane emissions. The mass balance method correctiy measured intermediate flux densities with a margin of error of less than 30%, but gave unsatisfactory results for very low values, that were overestimated by a factor of 10 to 20, and for very high values, that were underestimated by a factor of2. Problems with the Operation ofthe sampling System would appear to be at least partly responsible for the poor fünctioning of this method. The tracer gas method yielded good results for mid-range and high flux densities, with a margin of error of less than 20%. This method worked less well for low flow densities, that were overestimated by a factor of2.5 to 3.5, even though the actual values were always within the uncertainty margin. This problem does not seem to be linked to the method itself, but to the difficulties encountered in measuring low methane concentrations.

RESULTS

Accumulation Chamber Methods

DISCUSSION

This series of tests appears to establish the superiority of the INERIS method in the accumulation chamber method category, and that of the IPSN tracer gas method among the atmospheric methods. This conclusion must be nuanced, however. The final goal is to measure methane fluxes at actual municipal solid waste landfills, hence under conditions very different from the highiy favourable conditions of the INERIS test-bed or the Etouy site. For instance, in the case ofthe INERIS accumulation chamber method, the test-bed measurements were made using a gas-phase chromatography column that would be replaced by a portable detector in the field. It is known that the biogas emitted at landfill sites has a complex composition. Care must therefore be taken to avoid interference problems when detecting methane with this type of detector. Regarding the IPSN tracer gas method, this method works well in principle if the methane and the tracer gas are emitted in identical fashion. This condition was fillfilled in Etouy, because the two gases were emitted through the same network of injectors. But how can these conditions be respected at a real-life landfill, where methane fluxes will be unevenly distributed and not known prior to measurement? Inversely, the least effective methods in the comparison are not without relevance for real-life situations. The sensor mounted in the IPSN accumulation chamber is noteworthy for its low cost, light weight and low energy needs. Experimental conditions at the test site were probably not very favourable to the application of the INRA methods, particularly the eddy correlation method.

The detector used for this latter technique performed remarkably well.

In conclusion, on-site experimentation now appears indispensable. Plans are to retain one accumulation chamber method and one atmospheric method for this fürther work, äs the two types of method have not yet been compared directiy. In light of the above results it seems natural to retain the INERIS chamber method and the IPSN tracer gas method. It would be interesting, however, to include the IPSN TGS sensor in the loop that INERIS will install on its accumulation chamber. Likewise, it would be interesting to ascertain ifthe adjustable laser diode detector used by INRA can improve measurement of low methane concentrations. If so, the effectiveness of the tracer gas method for low flux densities could be markedly improved by using the laser diode detector äs a supplementary device.

NOTES

l. POKRYSZKA Z., TAÜZIEDE C., JODART A., (1994) (1994). Mesure de flux de methane par tracage gazeux sur le site d'emission contrölee d'Etouy du 13 au 16juin 1994. Rapport IPSN, contrat Ademe n° 3930020, Premiere partie, novembre, 30 pp.

5-

A

  comparison of methods for the measurement of methane emissions from municipal solid waste landfills for the purpose of evaluating their contribution to the greenhouse effect D. Savanne, Philippe Cassini, Zbigniew Pokryszka, Christian Tauziède, A. Tregoures, P. Berne, J.C. Sabroux, P. Cellier, P. Laville To cite this version: D. Savanne, Philippe Cassini, Zbigniew Pokryszka, Christian Tauziède, A. Tregoures, et al.. A comparison of methods for the measurement of methane emissions from municipal solid waste landfills for the purpose of evaluating their contribution to the greenhouse effect. 5. International Landfill Symposium "Regulation environmental impact & afftercare" (Sardinia'95), Oct 1995, S.Margherita di Pula, Italy. pp.475-479. ineris-00971948

Table l .

 l Comparison of methane measurement results using accumulation chamber methods with flow densities actually emitted at test-bed

	Atmospheric Methods
	Table 2. Comparison ofmeasurement results using atmospheric methods with actually emitted
	flux densities
	EMITTED		INRA
		FLUX		Eddy correlation method
		Average		relative
		density		micer-
	Nml/(m^.min)	tainty
				(%)
	AI	1.5		10%
	A2	5.0		3%
	A3	0.12		7%
	A4	1.5		10%
	A5	0.04		20%
	A6	10.45		4%
				BENCH	IPSN Chamber	INERIS Chamber
	Tests	average emitted	average emitted		average measured
			flux density Nml/(m 2 .min)	flux density Nml/(m^.min)	uncertainty factor	flux density Nml/(m^.min)	uncertainty factor
	d2			6.1	5	± 30%	6.0	±5%
	d2wind			6.1	11	± 30%	6.5	±5%
	d3			0.5	l	± 30%	0.5	±5%
	d4			180	71	± 30%	176.3	±5%
	d5			19	23	± 30%	19.2	±5%
	d6			20	16	± 30%	19.9	±5%
	d7			10	10	± 30%	9.6	±5%
	d7wind			10	11	± 30%	9.4	±5%
	The values for flow densities emitted by the test-bed are known within a relative uncertainty
	margin of ±5%. All the measurements determined by INERIS were correct. The results
	obtained with the IPSN chamber were less convincing. This chamber tended to underestimate
	high flux densities and overestimate low flux densities. In the most extreme cases the
	deviation from actual values reached 200%. Further test runs suggest that these deviations
	may be due to poor chamber design rather than to the sensor used.	_	-

  . Compte rendu de l'intercomparaison des methodes de mesure du flux surfacique de gaz par chambre du 16 au 20 mai 1994, resultats des mesures effectuees par 1TNERIS. Rapport INERIS, contrat Ademe n° 3930021, quatrieme partie, decembre, 12 pp. 2. SABROUX J.C., DAJLEVIC D., ESPIET F., MAUREL J.M., RICHON P., (1994). Intercomparaison des methodes de mesure des densites de flux surfaciques du methane par chambres d'accumulation, resultats et evaluation des mesures effectuees sur le banc d'etalonnage de l'INERIS du 16 au 20 mai 1994. Rapport d'etudes SERAC/LEIRPA/94-19, contrat Ademe n° 3930020,28 pp.3. CELLIER P., LAVILLE P., FLURA D.,TAUPIN F., (1994). Intercomparaison des methodes de determination des flux de methane emis par les decharges d'ordures menageres : correlations turbulentes et bilan de masse, Rapport INRA-Grignon, Unite de Biociimatologie, contrat Ademe n°3930022, decembre, 11 pp.

4. TREGOURES A-, BERNE P., GUELFF C., RAVENTOS C., SESTIER-CARLIN R.,


Richard-Le Naour

DOSE REPARTITION IN ALVEOLI, ALVEOLAR DUCTS AND BRONCHI OF RATS EXPOSED TO RADON AND ITS PROGENY, PRELIMINARY RESULTS

Keywords: Confocal microscopy, Micronuclei, Radon, Ozone, Pulmonary epithelial cells, Alveolar macrophages, Rats, Gamma rays

Rats were exposed to 2 ppm ozone for 5 hours to increase micronuclei formation in the different lung compartments one week after local irradiation.

Animals were exposed to either radon and its progeny (300 and 1000 WLM) or local lung external irradiation using gamma rays from cobalt-60 (7.5 Gy).

Animals were administered 5-bromo 2'deoxyuridine 18 and 12 hours before to label post replicative cells. They were killed 36, 48 and 60 hours after the beginning of the ozone exposures. Alveolar macrophages (AM) were recovered by lavage of the left lobe and the right lobes were fixed for histological studies using confocal microscopy.

Micronuclei measurements in AM did provide only mean dose estimate to the deep lung. Histological observations showed a nearly homogeneous irradiation by gamma rays whereas, heterogeneous irradiation seemed to occur after radon exposure with a gradual dose increase from alveoli to bronchi.

Introduction

Recently, micronuclei scoring has been performed to estimate doses delivered to the lungs after heterogenous irradiation induced after inhalation of radon and its progeny. These studies were limited to the deep lung after either extraction of alveolar macrophages (AM) by lavage (Taya et al., 1994, Johnson and[START_REF] Johnson | Estimation of the dose of radon progeny to the peripheral lung and the effect of exposure to radon progeny on the alveolar macrophages[END_REF] or enzymatic dissociation of lung cells to initiate fibroblast cultures [START_REF] Khan | Micronuclei induced by radon and its progeny in deep-lung fibroblasts of rats in vivo and in vitro[END_REF]. Dose estimates were performed after comparison with micronuclei formation induced in vitro by irradiation with alpha particles.

We have previously shown that, after irradiation, micronuclei formation can be greatly increased by an acute ozone exposure which transiently stimulates lung cell proliferation, mainly for epithelial cells and AM [START_REF] Bisson | Biological dosimetry in different compartments of the respiratory tract after inhalation of radon and its daughters[END_REF], we have also developed an experimental procedure to score micronuclei in post-replicative cells on lung thick sections by scanning confocal microscopy [START_REF] Bisson | Micronuclei scoring in irradiated lungs by confocal microscopy[END_REF].

The aim of this study was to provide qualitative and quantitative results to compare micronuclei induction in AM after radon and gamma ray exposure and to estimate dose distribution within the different lung compartments.

Material and methods

Male Sprague-Dawley rats (OFA, Iffa Credo, France), were used at 3 months of age. Five groups of animals were studied : rats exposed 1) to ozone alone, 2) to gamma rays from cobalt-60 and ozone, 3) to radon and ozone, 4) to radon alone and 5) unexposed controls. The irradiations were performed one week before the ozone exposure.

Ozone exposure was whole-body performed in a Hazleton inhalation chamber. Ozone was produced by passing pure oxygen through a silent electric arc-type ozoniser (WALLACE and TIERNAN BA 023012). The gas mixture was diluted with air to obtain a final concentration of 2 ppm which was monitered continously in the chamber with an analyser (O3 43M, Environnement S.A.).

The duration of exposure was 5 hours (Tredaniel et al., 1994).

Whole-body exposure to radon and its progeny was performed during 24 hours in the Razes facility to obtain either 300 or 1000 WLM (equilibrium factor : 0.80, "unattached" fraction : 0.08) [START_REF] Monchaux | Carcinogenic and cocarcinogenic effects of radon and radon daughters in rats: an overview of 20 years of study[END_REF]. 7.5 Gy local lung gamma irradiation was performed using cobalt-60 at a dose rate of 1 Gy/min. 5-bromo 2'-deoxyuridine (BrdU) (25mg/kg) and deoxycytidine (lOmg/kg) were administered 18 and 12 hours before killing to label cells which synthesize DNA. After pentobarbital anaesthesia, the left lung was lavaged, cells were counted and cytospin were observed after Giemsa staining, the right lobes were fixed in 4 % buffered paraformaldehyde for 3 days. Thick cryostat sections (80 (xm) of fixed tissue were stained by a primary antibody mouse anti BrdU and a secondary antibody: goat anti mouse FITC labelled. Cells were counterstaining by propidium iodine. Labelled cells were observed by scanning confocal microscopy as previously described [START_REF] Bisson | Micronuclei scoring in irradiated lungs by confocal microscopy[END_REF].

Results

In each group of irradiated rats, a nearly two-fold increase in the number of extracted AM was observed from 36 to 60 hours after the beginning of ozone exposure. This increase was similar to that observed in unirradiated controls.

Figure 1 shows the percentage of AM with micronuclei (MiAM) in irradiated rats either exposed or unexposed to ozone. In control rats unexposed to ozone, MiAM was 0.2 % ± 0.1 which was not significantly modified by the ozone exposure. In irradiated rats unexposed to ozone, similar MiAM were observed for 7.5 Gy and 1000 WLM but, the ozone exposure induced a larger increase of MiAM for 7.5 Gy than for 1000 WLM. For all post ozone exposure times studied, MiAM induced after 300 WLM was always less than that induced by 1000 WLM.

Observations by scanning confocal microscopy of micronuclei in alveolar tissue seemed to be in agreement with results obtained in extracted AM. By contrast, in the bronchial epithelium, the fraction of cells with micronuclei appeared similar for 7.5 Gy and 300 WLM and most of the cells had only one micronucleus. A larger fraction of micronucleated bronchial cells seemed to occur for 1000 WLM than for 7.5 Gy and 300 WLM. Because most micronucleated cells after 1000 WLM contained more than 1 micronucleus, we have measured in one animal the number of micronuclei per micronucleated cells in different lung compartments. Results are shown in figure 2. About 50 % of micronucleated alveolar cells contained only one micronucleus whereas, in alveolar ducts and in bronchi, this population corresponded to 43 % and 33 % of the total micronucleated cells respectively. The percentage of cells containing 4 micronuclei was higher in bronchi than in alveolar ducts or in alveoli, 25 %, 10 % and 5 % respectively .

Discussion

This study on AM confirms that ozone exposure increases micronuclei formation in irradiated rats and could be a useful tool for biological dosimetry [START_REF] Bisson | Biological dosimetry in different compartments of the respiratory tract after inhalation of radon and its daughters[END_REF]. The observed results did not provide an accurate value of dose equivalent for radon exposure but were consistant with that previously reported (1 WLM = 0.8 mGy alpha) [START_REF] Khan | Micronuclei induced by radon and its progeny in deep-lung fibroblasts of rats in vivo and in vitro[END_REF] taking into account for micronuclei induction a relative biological effectiveness of 10 for alpha versus gamma irradiation [START_REF] Brooks | Effectiveness of radon relative to acute 60 Co y-rays for induction of micronuclei in vitro and in vivo[END_REF]. Further studies are in progress to determine dose effect relationship for both homogeneous gamma irradiation and heterogeneous radon exposures, and the evolution of cellular alterations (spontaneous and ozone induced AM proliferation, micronucleated AM and multinucleated AM) as a function of post-irradiation time.

Although only preliminary results were obtained, the histological study provides new data for dose distribution estimate within lung tissues. Under the experimental exposure used, i.e. high equilibrium factor and low "unattached" fraction, a gradual increase of doses appeared to be delivered from the most distal lung to the bronchi. Thus, the maximal dose might not be delivered to the main target area for lung tumour induction which is located in the bronchiolo-alveolar junction [START_REF] Poncy | An experimental two-stage rat model of lung carcinoma initiated by radon exposure[END_REF] or in alveoli [START_REF] Cross | Influence of radon daughters exposure rate, unattachment fraction, and disequilibrium on occurence of lung tumors[END_REF].

These results are conflicting with dose repartition reported using mathematical model [START_REF] Hofmann | Radon progeny dosimetry in the rat lung[END_REF]. Further studies are in progress to provide more complete quantitative results and to determine the effect of exposure conditions to radon and its progeny on dose distribution in the different lung compartments.

Figure 1 :

 1 Figure 1: Evolution of micronucleated AM as the function of time following acute ozone exposure (mean values ± sd for at least 4 animals per group).

Figure 2 :

 2 Figure 2: Distribution of the number of micronuclei per cell in the different lung compartment (animal exposed to ozone one week after 1000 WLM and killed 60 hours later).

Figure 3 :

 3 Figure 3: Micronuclei within post-replicative cells of the bronchiolar epithelium. Observation performed by confocal microscopy after an exposure to 300 WLM and 48 hours after the ozone exposure (step between 2 successive view 2 \im).

Acknowledgement

This work was supported by CEC contract FI3PCT920021.


Eva Leotz Gartziandia

Angels Castellnoü

Norbert Gonzalez-Flesca

Patrick Carlier

Prot Agency

Phe Phenanthrene

F L Fluoranthene

ARTIFACT FORMATION IN HIGH VOLUME SAMPLING OF VOC's AND SOLID ORGANIC COMPOUNDS

Keywords: PAH, airbome particies, artifacts, high volume sampling. ABREVIATIONS AC

Pollutants from vehide emissions and many other combustion sources at ambient temperature, include gaseous (VOC's) äs well äs solid (SOC's) organic compounds. High volume samplers are commonly used m air quality monitoring especially m urban areas. Equipment commercially available is able to collect the gaseous and the solid fractions ofan ambient air sample. Nevertheless the quality of the sample can be seriously degraded by the presence of co-pollutants. This work outlines the artifact fonnation by evaporation and chemical reaction of ozone with some atmospheric PAH's. It is shown that the PUF back up leads to a good recovery only in over exposure experiments with purified air. However recoveries become poor and variable when sampling polluted air.

Purified air containing 180 ppbv ozone seems to destroy PAH according to already published reactivity scales.

It appears that a number of complex and unmastered physicochemical phenomena take place in a high volume sampling. The problem of the reliability of such measurements is raised.

INTRODUCTION

Large amounts of organic matter are mtroduced into the atmosphere from mdustrial activities, transport, natural and even domestic sources. However, one can consider äs pollutants only those compounds that are able to produce some measurable effect on humans, animals, plant life or materials (l). Several ofthese compounds have been subject to control because their primary toxicity or their role in secondary pollutants formation.

Organic compounds in the troposphere are gaseous (VOC's) or solids (SOC's) at ambient temperature. The phase partitionmg ofthese compounds at emission will be transformed once in the atmosphere through a number of physicochemical transformations including photochemical reactions. This ability to transform will lead during sampling to modification in the sample composition. Such modifications are called artifacts. The phase partitioning is important since it dictates the pollutants life time hence their transport ränge and accumulation in the atmosphere. These facts are directiy linked to health risks [START_REF] Albaiges | Vapor-partide partitioning of hydrocarbons in westem Mediterraneall urban and marine atmospheres[END_REF].

Polycyclic Aromatic Hydrocarbons (PAH's) is a chemical group that has generated a great interest. They are produced during the combustion of organic material. Thus there are numerous PAH's sources such äs the combustion of coal, petrol, diesel, wood but also incineration plants. The systematic occurrence of certain PAH's can be usefül when characterising emission sources e.g. PHE, FL and PYR are predominant in diesel emissions while BaP, IP and COR are commonly found in petrol füeled vehicie emissions [START_REF] Masciet | Identification des sources d'hydrocarbures aromatiques polycycliques particulaires dans l'atmosphere urbaine[END_REF].

PAH molecular structure consists of between two and ten hydrocarbon rings (mainly aromatics). Even though the number of PAH that can be found in the atmosphere is large, regulatory bodies tend to focus their concem according to human health risk, probability to produce environmental transformations and or metabolic alterations [START_REF][END_REF]. In some cases the PAH toxicity, mutagenicity and carcinogenicity have been documented [START_REF] Finlayson-Pitts | Chemistry and mutagenic activity of airbome polycyclic hydrocarbons and their derivatives[END_REF][START_REF] Degobert | [END_REF][START_REF] Grimmer | Relevance of polycyclic aromatic hydrocarbons äs environmental carcinogens[END_REF]. Most of the PAH studied here are those ofthe EPA method TO-13 [START_REF]GC) and high performance liquid Chromatographie (HPLC) analysis[END_REF].

In addition to health concems, PAH's are known to participate in tropospheric chemistry [START_REF] Masciet | La chimie atmospherique des hydrocarbures aromatiques polycycliques[END_REF] since they can react with many species present such äs N02, [START_REF] Finlayson-Pitts | Chemistry and mutagenic activity of airbome polycyclic hydrocarbons and their derivatives[END_REF][START_REF] Brorstrom | Transformation of polycyclic aromatic hydrocarbons during sampling in ambient air by exposure to different oxidized nitrogen compounds and ozone[END_REF][START_REF] Lindskog | Transformation ofreactive PAH on particies by exposure to oxidized nitrogen compounds[END_REF], 03 [START_REF] Davis | A review of sampling methods for aromatic hydrocarbons in air[END_REF]. From this chemistry, a qualitative reactivity scale has been established [START_REF] Finlayson-Pitts | Chemistry and mutagenic activity of airbome polycyclic hydrocarbons and their derivatives[END_REF][START_REF] Masciet | La chimie atmospherique des hydrocarbures aromatiques polycycliques[END_REF]: BaP>ANT>DBahA>BaA>BeP>PY>BkF>BbF Apart from PAH, many other molecules are present in the organic fraction ofairbome partides (aliphatic hydrocarbons, polar compounds, etc).

Aliphatic hydrocarbons are molecules containing 16 to 36 carbon atoms. They are commonly found m urban atmospheres [START_REF] Aceves | Large and small particie size screening of organic compounds in urban air[END_REF].

Polar compounds are mainly alcohols, organic acids and their derivatives containing chains of 14 to 32 carbon long. While less attention has been paid to this fraction, it has been shown that respiratory disorders are related to an increase ofconcentration ofhigh molecular weight alcohols [START_REF] Aceves | Identification of soybean dust äs an epidemic asthma agent in urban areas by molecular marker and RAST analysis of aerosols[END_REF].

EXPERIMENTAL

Considering that SOC's and VOC's coexist, the sampling equipment should be able to collect both phases. Apparatus used in this study is illustrated in figure l.

It consists of a metallic conical holder supporting the front filter (Whatman quartz fiber 10.16 cm diameter, 99.99 % efficiency for 0.3 um particulates) to collect partides, followed by a glass cartridge containing a back up adsorbent (PUF, 6.4 cm D. and 8 cm heigh). A volume of about 100 m3 is drawn through the holder by an electrically driven turbine at a typical flow rate of 13 m3/h. The whole assembly is contained in an aluminium cabinet. Punfied air for over exposure and ozone reaction experünents was obtained from an air generator fully described elsewhere [START_REF] Jaouen | A dynamic polluted atmosphere generator at low ppbv levels for validating VOC sampling methods[END_REF]. The air generator filter is shown in figure 2.

Ozone air stream was generated by high voltage discharge in oxygen. Ozone concentration was measured by an U.V. absorption ozone analyser.

Samples preparation

Laboratory materials such äs silica gel, alumina, Soxhiet cartridges and PUF were extracted with dichloromethane for 48 h prior to use.

After sampling, PUF and filter were frozen at -4°C until analysis in the laboratory. Then they were Soxhiet extracted with dichloromethane for 24 h. The extract was vacuum and nitrogen evaporated until near dryness and diluted to l ml with dichloromethane, then fractionated by column chromatography. A column filled with l g each of 5% water-deactivated alumina (top) and silica (bottom) was used. The aliphatic hydrocarbons were obtained in the first fraction (4 ml of n-hexane), and the aromatic hydrocarbons were collected in the second fraction (4 mL of 20% dichloromethane in n-hexane). These two fractions were nitrogen concentrated almost to dryness and the residue dissolved in l ml dichloromethane. This method has been successfully used in previous studies [START_REF] Rosell | The composition of volatile and particulate hydrocarbons in urban air[END_REF][START_REF] Aceves | Analysis of hydrocarbons in aquatic Sediments. II. Evaluation of common preparative procedures for petroleum and chlorinated hydrocarbons[END_REF][START_REF] Aceves | Gas Chromatographie screening of organic compounds in urban aerosols. Selectivity effects in semi-polar columns[END_REF].

Instrumental analysis

The samples were analysed by GC-FED, with a Carlo Erba Model 5300 gas Chromatograph equipped with a flame-ionization detector and a splitless injeetor. Capillary column was a 30m x 0.32 mm i.d. PTE-5 (surface film thickness 0.25 um). Helium was the carrier gas (1,7 cc/min). The injeetor and the detector temperatures were 250° and 300°C respectively. The injection was in the splitless mode (hot needle technique). The oven temperature program was äs follows: 35°C (l mn)-5°/min -250°C-2.5 0 /Inin-255 0 C-3 0 /min-300 0 C (15 mm).

RESULTS AND DISCUSSION

Several experiments were carried out in a systematic way in an order of increasing complexity ranging from simple injection repeatabüity study to a field campaign including the füll analytical protocol. This was done in the aim of highiighting the artifact formation.

Injection repeatability

In order to assess the Chromatographie technique a series of seven injections of a 16 PAH Standard mixture was performed. The chromatogram is shown in figure 3. The relative Standard deviations ofpeak areas ranged between 5 % and 20% with a half better than 10%. Taking into account that samples were manually injected , this result seems acceptable. The relative Standard deviation of retention times was in nearly all cases better than 0.2 %, This precision was useml when identifying unknown compounds.

Recovery efficiency

In order to detect any possible loss of sample during sample preparation (extraction, concentration, etc) the filter was seeded with a small amount of two PAH having different volatilities: ANT

Volatility experiment

The partial Sublimation of SOC's during high volume sampling has been observed [START_REF] Finlayson-Pitts | Chemistry and mutagenic activity of airbome polycyclic hydrocarbons and their derivatives[END_REF]. The transfer of ANT and DBahA from the filter to the PUF backup was studied.

Purified air was drawn through a seeded filter for 7.3 hours at 13 m3/h. Results are reported in table 2. It is shown that the partition between the filter and the PUF are in agreement with the volatility of the compounds. The total recovery is higher than 90%. At this stage one can see that an adsorbent back up is an appropiate solution for a better recovery. Nevertheless, äs it will be shown later on, the over exposure in ambient air will lead to much different results.

Ozone artifact

Tropospheric ozone levels can be sufficient to react with PAH being collected in a high volume sampler. Recovery of sixteen PAH in an over exposure experiment with ozone was investigated. The experiment was conducted in the following way: filter was seeded with known amounts of PAH. The filter and the PUF were exposed to two purified air streams, one containing ozone and the other none. Results are reported in table 3. It is seen that all PAH more volatile than ANT are badly recovered. Three possible explanations are: some loss during sample manipulation [START_REF] Gonzälez-Flesca | Analyse des HAP dans les effluents industrieis humides[END_REF], reaction with ozone or, more likely, due to the PUF breakthrough. Table 3 PAH that are less volatile than ANT are well recovered m the filter and the PUF according to their molecular weight m the purified air experiment. However, when exposed to an ozone air stream, certain PAH (ANT, BaA, BaP and IP) are poorly recovered. One can explain this result by a possible ozonolysis especially ifwe take into account their reactivity.

Field measurements

Two campaigns were carried out in France, one in an urban site (Creil) and the other in a semi rural site (Marignane). As far äs FID was used, and due to the complexity of a natural sample, the Separation technique of aromatics and aliphatics was applied. Three organic compounds, namely ANT, DBahA and hexadecane were used äs indicators in a ränge of concentration higher than that usually found in ambient air. Results It is observed that organic compounds are in the PUF rather man in the filter aecording to the volatilisation artifact. One can expect that the extent ofthis artifact depends on temperature. There was a good Separation of aliphatic and aromatic fractions. Aliphatics were not identified but chromatograms in figure 4 suggest that aliphatics can be a large part of the total organic matter in an airbome particie.

CONCLUSIONS

A systematic study of artifact formation, especially volatilisation and reaction with ozone for some PAH of atmospheric interest was perförmed. A purified air generator was used to show that there is a large transfer from the filter to the PUF back-up. The gas/solid partitioning m the troposphere caimot be obtained directiy from the filter and the PUF recoveries.

The new air quality control directive specifies that PAH are one of the pollutants that shall be considered.

It appears that a number of complex and umnastered physicochemical phenomena take place during high volume sampling. Therefore further studies are merited in order to improve these type oftechniques.

  Figure l .High volume sampler holder.

Figure 2 .

 2 Figure 2. Air generator filter. A: 10 kg activated charcoal B: glass microfiber filter.

Figure 3 ,

 3 Figure 3, Standard mixture chromatogram.Recovery efficiencyIn order to detect any possible loss of sample during sample preparation (extraction, concentration, etc) the filter was seeded with a small amount of two PAH having different volatilities: ANT and DBahA. Results are shown in table l. It can be seen that no significant amount of sample is lost during this manipulation.

Table l .

 l and DBahA. Results are shown in table l. It can be seen that no significant amount of sample is lost during this manipulation.

	PAH	Average	RSD
		recovery %	n=3
	ANT	93	3.8
	DBahA	81	13
	PAH	Average recovery %		RSD n=2
		Filter	PUF	Total	Filter	PUF
	ANT	6	88.5	94	0	2.4
	DBahA	92	4.5	96	12	141

Table 2

 2

ACKNOWLEDGEMENTS

We particularly thank Mr Gwyn Jones for technical assistalice.

Some aromatics were identified and quantified including the indicators. The presence of PHE, FL and PY, especially in Creil Road Side, can be noticed. These PAH's are recognised äs oil combustion indicators. At the period ofthe year in which the sampling took place (summer time) their origin can be attributed to diesel engine combustion only. A very significant finding is that the over exposure of indicators in a natural and polluted air stream, leads to variable and poor recoveries. Many hypolhesis can be advanced to explain this variance: chemisorption on carbonaceous particies, chemical reaction with co-pollutants (03, NOx, SOC's, etc), PUF breaktrough volume modification, etc.

The remarkable inference of diese results is that if unknown and incontrolable factors degrades high volume VOC's and SOC's sampling the problem ofthe reliability ofsuch measurements is raised.