Wenjuan Wei

Olivier Ramalho

Corinne Mandin
email: corinne.mandin@cstb.fr

Indoor Air Quality Requirements in Green Building Certifications

Keywords: Rating, green building, volatile organic compounds (VOCs), formaldehyde, sustainable building

Green building certifications aim to achieve sustainable buildings that are healthy, energysaving, and environmentally friendly. To construct healthy built environments for occupants, a high indoor environment quality (IEQ) has to be maintained. The goal of this paper is to analyze how and to what extent indoor air quality (IAQ), as a subset of IEQ, is taken into account in green building certifications worldwide. Thus, IAQ requirements were reviewed in 31 green building certifications from 30 countries worldwide. These certification programs include 13 countries in Asia, 9 in Europe, 5 in Americas, 2 in Oceania, and 1 in Africa. Fifty-five green building schemes were selected from among the 31 certifications. Rating systems are commonly used in green building schemes to evaluate the capability and level of a building to achieve lifecycle sustainability. The average contribution of IAQ to green building schemes worldwide is 7.5%. Volatile organic compounds (VOCs), formaldehyde, and carbon dioxide (CO2) are the indoor air pollutants most frequently considered. Ozone (O3) and semi-volatile organic compounds (SVOCs) are mentioned in less than 6.7% of the certifications worldwide. Emission source control, ventilation, and indoor air measurement are the three main pathways used in green building schemes for IAQ management. All of the certifications include ventilation as a way to manage IAQ. Emission source control is included in 77% of the certifications and is mainly targeted at building material emissions. Indoor air measurement is included in 65% of the certifications but may be optional.

Introduction

Green building, also known as sustainable building, is the practice of creating structures and using processes that are environmentally responsible and resource-efficient throughout a building's life-cycle [START_REF]Green building basic information[END_REF] . "Green buildings" refer to the structures created using the principles and methodologies of sustainable construction [START_REF] Kibert | Sustainable construction: green building design and delivery[END_REF] , which aim to construct energy-efficient, healthy, and productive buildings that reduce the significant impact of buildings on urban life and the global environment [START_REF] Judelson | The green building revolution[END_REF] . The history of green building design began in the late 1980s when sustainability was defined by the United Nations' World Commission on Environment and Development [START_REF]Our common future, chapter 2: towards sustainable development[END_REF] . Pioneering work on green building certification was achieved in the early 1990s in Europe and the United States, including the BRE Environmental Assessment Method (BREEAM) certification in the United Kingdom, Haute Qualité Environnementale (HQE) certification in France, and Leadership in Energy and Environmental Design (LEED) certification in the United States. Following these developments, many additional countries worldwide have joined the green building effort in the past two decades and have developed green building schemes adapted to national economic and environmental conditions.

To achieve sustainability in buildings, green building schemes usually include several categories.

The LEED v4 scheme for building design and construction, for example, comprises location and transportation, sustainable sites, water efficiency, energy and atmosphere, materials and resources, indoor environmental quality, innovation, and regional priority [START_REF] Green | LEED v4 for building design and construction[END_REF] . The categories in the BREEAM scheme for new construction differ slightly from those used by LEED, comprising management, health and well-being, energy, transport, water, materials, waste, land use and ecology, pollution, and innovation [START_REF]BREEAM UK new construction non-domestic buildings technical manual[END_REF] . Although the categories vary among different green building schemes, the schemes' detailed requirements share many similar traits.

Indoor environment quality has a significant impact on modern life around the globe. Americans, on average, spend approximately 90% of their time indoors [START_REF]Report to Congress on indoor air quality[END_REF] . Most of the time spent indoors occurs at home (67% on average for the French population) [START_REF] Kirchner | Quality of indoor air, quality of life, a decade of research to breathe better, breathe easier. French Indoor Air Quality Observatory[END_REF] . Indoor air pollutants, such as volatile organic compounds (VOCs), microbes, particles, etc., have negative effects on the health of indoor occupants. A number of studies on emission mechanism and health effect of indoor air pollutants have been carried out [START_REF] Yu | A review of the emission of VOCs from polymeric materials used in buildings[END_REF][START_REF] Yang | Numerical simulation of VOC emissions from dry materials[END_REF][START_REF] Katsumata | Measurement of semi-volatile organic compounds emitted from various types of indoor materials by thermal desorption test chamber method[END_REF] . According to the "Guidelines for Air Quality" published by the World Health Organization (WHO), the main health effects of indoor air pollution include irritation, respiratory infection, and Sick Building Syndrome (SBS), among others. [START_REF]Guidelines for air quality[END_REF] Hence, to guarantee the health of occupants in buildings, it is important to maintain high indoor air quality (IAQ).

The objectives of this paper are to review recent green building certifications and their schemes worldwide and to analyze how and to what extent IAQ is taken into account. The final goal is to provide a global overview of the IAQ sections included in the considered certifications and to identify possible means of improvement if relevant.

Material and Methods

Inventory and selection of green building certifications

To identify and select the green building certifications used in this study, three steps were carried out: (1) Search for green building certifications in scientific peer-reviewed literature, reference books, and on the Internet to include as many certifications as possible. International certifications that are applied in multiple countries, such as LEED, which applies in the USA, Mexico, Brazil, Argentina, Singapore and, until recently, India, are considered to be the same certification and are counted only once. (2) Access the official websites of the identified green building certifications and download the most recent free versions of schemes released within the past six years. For certifications that have different schemes for different types of buildings, e.g., new, existing, residential, and non-residential buildings, all the schemes are reviewed and considered as different requirements that are applied to different conditions in the certification.

(3) Examine each scheme to see whether it has an IAQ section, and choose the final schemes for detailed analysis. Schemes for which a full-text version was not accessible or not free of charge were excluded.

All the certifications have a section that evaluates IAQ. Ultimately, 31 certifications from 30 countries worldwide (13 in Asia, 9 in Europe, 5 in Americas, 2 in Oceania, and 1 in Africa) were retrieved, comprising 64 schemes that are applied to different types of buildings. Most of the green building schemes are written in English. The remaining schemes are written in the local language (e.g., French, Italian, and Chinese). Of the 64 schemes, one Vietnamese scheme was excluded because of language limitations, and eight other schemes were excluded because they were not accessible. A total of 55 schemes are reviewed in this paper, as shown in Table 1. The countries and certifications do not match one to one. Some countries, such as Canada and the United States, have several different green building certifications, and some certifications, such as LEED and BREEAM, are applied in multiple countries, as shown in Figure 1.

Contribution of IAQ in green building certifications

Rating methods in green building schemes

Rating systems are universally used in green building schemes. To achieve building sustainability, the requirements can be divided into several categories, such as energy efficiency, water, and health. In each category, there are several sections, such as IAQ, lighting, and thermal comfort. In each section, several requirements are defined in detail. For each requirement in a green building scheme, a scoring system is used to evaluate to what extent the requirement is achieved. The total final score represents the life-cycle sustainability of the building and is calculated after all the requirements in the scheme are evaluated. Therefore, the total final score is a function of the scores in the respective categories, sections, and requirements, as shown in Equations ( 1) - (3).

Final = f1 ( (Category)1 , … , (Category)n ), n = 1, 2, 3, … (1)
(Category)n = f2 ( (Section)1 , … , (Section)m ), n = 1, 2, 3, …; m = 1, 2, 3, … (2)
(Section)m = f3 ( (Requirement)1 , … , (Requirement)i ), m = 1, 2, 3, …; i = 1, 2, 3, … (3)
In general, three types of rating methods are used to calculate the total final score. The first approach is a point-based scoring method, such as in LEED. In this case, scores are assigned as points. Each requirement earns a certain number of points depending on how it is fulfilled. The total final score is defined by the number of requirements that are met and the corresponding sum of all points earned. For this method, Equations ( 1) -( 3) are redefined as Equations ( 4) -( 6).

 = n n Category Final 1 ) ( , n = 1, 2, 3, … (4)
 = m m n Section Category 1 ) ( ) ( , n = 1, 2, 3, …; m = 1, 2, 3, … (5)
 = i i m quirement Section 1 ) (Re ) ( , m = 1, 2, 3, …; i = 1, 2, 3, … (6)
The second rating method is a weighted approach, such as in BREEAM and NABERS. Points are assigned to each requirement to evaluate to what extent it has been fulfilled. For each category, the score is the ratio of the points achieved and the maximum points available in the category, represented as a percentage. For example, the score in a category is 100 if all the requirements in the category are met. Different weighting values are employed for the categories to indicate their non-uniform importance when calculating the total final score. For this method, Equations ( 1) -( 3) are redefined as Equations ( 7) -( 9).

) ) ( ) (( 1 n n n Weighting Category Final  =  , n = 1, 2, 3, … (7)
% ) int ( ) ( % ) ( 1 n m m n s MAXpo Section Category  = , n = 1, 2, 3, …; m = 1, 2, 3, … (8)
 = i i m quirement Section 1 ) (Re ) ( , m = 1, 2, 3, …; i = 1, 2, 3, … (9)
The third rating method comprises additional evaluations that are more complicated or unique.

These evaluations vary among green building schemes and are thus difficult to summarize.

Among the 31 certifications, 12 use a point-based scoring method, 8 use a weighted method, and 4 use other, more complicated calculation methods. Finally, there are 7 certifications in which the rating systems are not clear because some categories or sections that are not relevant to IAQ are missing from the download schemes.

Buildings can be certified at different levels. There are 4 levels in LEED certification, i.e., Certified, Silver, Gold, and Platinum. There are 6 levels in BREEAM certification, i.e., Unclassified, Pass, Good, Very good, Excellent, and Outstanding. The levels of green building certification are mainly based on the total final score. Veto requirements in some categories are also commonly introduced in addition to the total final score to determine the level of certification. Veto requirements are not consistent across different green building schemes and are thus not discussed in further detail here.

Contribution of IAQ to green building certifications

IAQ is taken into account in all of the retrieved green building certifications. The contribution of IAQ to a green building scheme can be quantified if the first or second rating methods are used to calculate the total final score. For the first (point-based) rating method, the contribution of IAQ to the green building scheme is the ratio of the maximum points in the IAQ section to the maximum total final points. For the second (weighted) rating method, the contribution of IAQ to the green building scheme is the ratio of the maximum score in the IAQ section to the maximum total final score.

The average contribution of IAQ to the 20 point-based or weighted green building certifications worldwide is 7.5%, as shown in Figure 3. In general, American green building certifications place more emphasis on IAQ compared with systems used in other countries. The average contribution of IAQ to American green building certifications is 9.4%. However, the highest contribution of IAQ worldwide is 10.6% for Tree certification in Thailand. The highest contribution of IAQ to European certifications is 10% for KLIMA certification in Austria.

Among the 20 point-based or weighted certifications, 8 include different contributions of IAQ within their respective schemes, as shown in Table 3. Nevertheless, these different contributions retain the same order of magnitude. European green building certifications recommend low-formaldehyde-emission wooden-based panels that are labeled E1 according to ENV 717-1 (2004). In other countries, such as USA, wooden products that do not contain urea-formaldehyde resin are required. Government efforts are important for reducing formaldehyde emission as well as influencing green building schemes.

In Japan, reducing the emission of chemical pollutants from building materials is mandatory and included in the national Building Standards Law. Some certifications include additional requirements related to outdoor air intake and the filters used in ventilation systems to prevent gaseous and particulate pollutants from entering the building; these requirements are listed in Table 5.

Figure 7. Standards for ventilation management in green building certifications worldwide Table 5. Requirements for outdoor air intake and ventilation system filters Certification Requirements CASBEE Air intakes must be located away from sources of pollution.

IGBC

Outdoor air intakes must be located a minimum of 7.6 m from outdoor smoking areas;

Install air filtering media after building flush-out, using at least MERV 13, EU 7 or equivalent.

SI 5281

Building's air intakes and exhausts must be more than 10 m apart;

If a source of external pollution exists, the ventilation system must filter the air.

Pearl Separation distances required between outdoor air intakes and any exhausts or discharge points;

Establish 25-m smoke-free zones around outdoor air intakes;

Outdoor air intakes must be placed away from known sources of pollution;

Installation of MERV 8 or G4 class filters in each return air grille.

BEAM Plus Air intakes are sited away from pollutant sources and avoid short-circuiting with exhausts;

Filters are effective in removing outdoor pollutants.

BREEAM

Building's air intakes and exhausts are more than 10 m apart, and intakes are more than 20 m from sources of external pollution. LEED Each ventilation system that supplies outdoor air to occupied spaces must have particle filters;

Filtration medias are installed at each return air grille and return or transfer duct inlet opening to avoid bypass around the filtration media.

Green

Globes

Exhaust outlets and plumbing vent stacks located at least 6 m away from outdoor air intakes;

Outdoor air intakes located at least 9 m away from sources of pollution;

Outdoor air intakes protected with 6.4 mm or smaller mesh screens.

GPRS Separation distances required between outdoor air intakes and any exhausts or discharge points;

Outdoor air intakes are located a minimum of 25 m from outdoor smoking areas.

Indoor air measurement

Indoor air measurement can take place before or during indoor occupancy, depending on the certification. There are 20 green building certifications comprising 25 schemes that propose indoor air measurement. In 21 schemes, such as GB/T 50378, IGBC, and NABERS, indoor air measurement is mandatory but to varying degrees. Assessment points for indoor air measurement can be guaranteed only if the results of measurements meet requirements. In the other 4 schemes, including LEED, HQE, and BREEAM, indoor air measurement is optional due to the presence of alternative options for managing IAQ or depending on the level of certification. In the schemes that propose indoor air measurement, the thresholds of IAQ pollutants vary depending on the level of certification. Five pollutants of concern are indicated on every continent: CO2, formaldehyde, TVOCs, CO, and PM10, as shown in Figure 8. On average, three parameters are measured in each certification. Indoor air sampling strategies are not mentioned in detail in most of the certifications that propose indoor air measurement. Detailed information is provided in seven out of the twenty certifications (LEED, IGBC, BEAM Plus, HQE, BREEAM, KLIMA, and NABERS). Sampling strategies vary among the certifications. In general, the number and location of sampling points depend on the size of the building and must represent "normal" occupied spaces. Table 6 shows the details of sampling strategies used in different certifications. Detailed information on how to measure indoor air pollutants is usually not included in green building schemes. For CO2 and CO, continuous monitoring devices are commonly used. For other compounds, it is not clear whether active sampling or passive sampling is recommended.

No common international standard on indoor air pollutant measurements exists for all certifications. However, five out of the nine certifications that propose the measurement of indoor formaldehyde concentrations follow the ISO 16000-3 standard, and four out of the eight certifications that propose the measurement of indoor TVOC concentrations follow the ISO 16000-6 standard; these standards are summarized in Table 7. ISO 16000-3 is suitable for the determination of formaldehyde in the approximate concentration range from 1 µg/m 3 to 1 mg/m 3 .

The measurement procedure involves active sampling of formaldehyde from air on adsorbent cartridges coated with 2,4-dinitrophenylhydrazine (DNPH), followed by subsequent analysis using high-performance liquid chromatography (HPLC) [START_REF]Indoor air -Part 3: Determination of formaldehyde and other carbonyl compounds in indoor air and test chamber air -Active sampling method[END_REF] . ISO 16000-6 is suitable for the determination of VOCs in indoor air. The measurement procedure involves active sampling of VOCs from air on Tenax TA sorbent with subsequent thermal desorption (TD) and gas chromatographic (GC) analysis [START_REF]Indoor air -Part 6: Determination of volatile organic compounds in indoor and test chamber air by active sampling on Tenax TA sorbent, thermal desorption and gas chromatography using MS or[END_REF] . to WHO guidelines for IAQ, a short-term (30-minute) guideline of 100 µg/m 3 is recommended for indoor formaldehyde concentrations to prevent sensory irritation in the general population [START_REF]WHO guidelines for indoor air quality: selected pollutants[END_REF] .

Therefore, indoor formaldehyde concentrations in the green buildings that are certified at higher levels might not achieve the WHO guideline.

Discussion

Limitations of the analysis

Although the existing certifications were inventoried as exhaustively as possible, some certifications may be missing. Certifications that lack an English translation and are not mentioned in English-language publications are unlikely to be found. In general, most of the certifications reported in this study are written in English. Others are written in French, German, Italian, Spanish, Chinese, Indonesian, and Thai. There may exist certifications written in other languages that are missing from this study. In addition, green building certifications that are not accessible online or are not free of charge are not included in this study for practical reasons.

Moreover, green building schemes that provide only a brief summary of IAQ and other sections or those that do not provide a full text regarding IAQ are not included in this study. This study shows the need for transparency to allow the comparison and normalization of green building schemes worldwide.

Target indoor air pollutants

Indoor air pollutants that are taken into account in WHO ambient and indoor air guidelines include SO2, airborne particles, NOx, CO, CO2, water vapor, mold spores, radon, pollen, lead, manganese, cadmium, mercury, arsenic, asbestos, ammonia, ozone, nicotine, acrolein, allergens, viable organisms, VOCs, polycyclic aromatic hydrocarbons (PAHs), formaldehyde, benzene, naphthalene, trichloroethylene, and tetrachloroethylene [START_REF]Guidelines for air quality[END_REF][START_REF]WHO guidelines for indoor air quality: selected pollutants[END_REF][START_REF]WHO Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide: global update 2005: summary of risk assessment[END_REF] . The pollutants in the WHO guidelines that are also considered in green building certifications include SO2, NOx, CO, CO2, radon, asbestos, ammonia, ozone, nicotine, VOCs, formaldehyde, benzene, and particulate matter. Thus, most of the priority compounds are considered in the studied certifications.

Ozone, known as a reactive chemical, can react with human skin lipids and generate carbonyl, carboxyl, and α-hydroxy ketone [START_REF] Wisthaler | Reactions of ozone with human skin lipids: sources of carbonyls, dicarbonyls, and hydroxycarbonyls in indoor air[END_REF] . Photocopiers and printers in offices are known to emit ozone during use. However, indoor ozone contamination is only taken into account in LEED, BEAM Plus and HQE certifications. Given the negative health effects of this compound, the regulation of ozone via indoor emission source control and measurement in green building certifications might need to be improved in the future.

Indoor particle pollution varies from country to country and from region to region. Indoor Developing industrial countries, such as China, have severe indoor particle pollution due to high particle concentrations in outdoor air. However, the control of indoor particle concentrations is not included in green building schemes in such countries. Improvements to these schemes might be needed in the future.

SVOCs are a group of chemical pollutants with a high residence time indoors. Indoor sources of SVOCs include pesticides, plasticizers, flame retardants, etc. Suspected negative health effects of SVOCs include cancer and endocrine disruption, among others [START_REF] Bornehag | The shift in human health from infection-related diseases to chronic illnesses and the importance of indoor chemical exposure[END_REF] . These man-made chemicals are increasingly used in modern built environments. However, in the 31 green building certifications reviewed, control of indoor SVOC concentrations is only mentioned in the KLIMA certification in Austria. In the KLIMA scheme for new office buildings, indoor SVOC sources include paint, sealant, plaster and filler, and wooden materials. Detailed information on how to control indoor SVOC sources is not provided in this scheme. In the KLIMA scheme for new residential buildings, stricter requirements are included for indoor SVOC emission source control. The total SVOC content should not exceed 100 µg/m 3 in emission test chambers for wooden flooring, floor coverings, and other wooden materials. In addition, the total SVOC content should not exceed 2% of the weight of flooring coatings. SVOC emission source control in other building materials, as well as measurement of indoor SVOCs, is not required in the KLIMA certification.

Different concerns between certifications

Requirements on IAQ in residential buildings and non-residential buildings are consistent.

Differences between new buildings and existing buildings occur because of a variety of requirements on indoor environment design and construction for new buildings and a number of requirements on indoor environment performance for existing buildings. For example, requirements on VOC source control mostly focus on choosing low-VOC-emission materials for new buildings and establishing green cleaning techniques for existing buildings.

The different concerns between certifications in various countries may due to a number of reasons. For example, laws and regulations on indoor environment vary between countries due to political, economical, and environmental variations. Thus, green building certifications in different countries pay attention to various indoor air pollutants and have different methods to evaluate IAQ. Most commonly, certifications appear as a voluntary complement to national regulations. Some countries include green building directly in their national building regulations.

For example, the government of Dubai has listed several green building requirements in its regulation for new residential and non-residential buildings [START_REF]Green building regulations & specifications[END_REF] . Therefore, when green building specifications or specific indoor pollutant guidelines are defined in national regulations, the accompanying certification does not include such guidelines, as they are already required by law.

As such, the comparison between certifications is even more difficult. A similar comparison of national regulations is required to precisely define which indoor air quality criteria are taken into account in green building processes.

Conclusions

Fifty-five green building schemes in 31 certifications worldwide were reviewed. IAQ is included in all of the certifications as a section that evaluates the health risk of indoor occupants. The global average contribution of IAQ in green building certification is 7.5%. A large variety of compounds are targeted. Some compounds, e.g., ozone, particles, and SVOCs deserve to be considered in a larger number of certifications due to their negative health effects. All of the certifications include ventilation as a way to manage IAQ. Emission source control is included in 77% of the certifications and is mainly targeted at building material emissions. For existing buildings, other emission source control pathways should be more widely considered, such as the reduction of emissions due to cleaning products and cleaning practices. Very few schemes consider this issue, possibly due to the lack of existing tools, standards and labels to characterize the VOC emissions from these products. Indoor air measurement is included in the majority of the certifications (65%). However, the sampling strategy, the sampling and analytical methods, and the guidelines used to qualify the results are not often precisely described and appear to be highly variable.

In conclusion, IAQ is taken into account in all the green building certifications considered, and equal emphasis is placed on the two major ways to improve IAQ: emission source control and ventilation. Some possible improvements are identified. This paper has shown the need for transparency to allow the comparison and normalization of green building schemes.

Opportunities to harmonize the different approaches used worldwide should be pursued in the future.

Figure 2 .

 2 Figure 2. Review procedure for the IAQ section within certifications

Figure 8 .

 8 Figure 8. Indoor air pollutants targeted for indoor air measurement

  particle control is required in four certifications (BEAM Plus, IGBC, HQE, and LEED). BEAM Plus certification mainly focuses on outdoor particle source control, whereas the other three certifications require measurements of indoor PM10 concentrations. PM2.5 concentrations are measured in HQE and LEED certifications. The thresholds of PM2.5 concentrations in indoor air are 10 µg/m 3 annually or 25 µg/m 3 daily in the HQE scheme and 15 µg/m 3 in LEED scheme.

Table

  . Summary of the green building certifications and schemes considered types of buildings, as shown in Table2. A green building certification has at least one scheme that can be applied to one type of buildings.However, for most of the certifications, some different schemes apply to different types of buildings. Table 2 lists all the schemes identified in this study, according to the countries where the certifications are created or most commonly applied.

	Table 2. Sources referenced for major green building schemes Certification New Existing New & existing N-R * R ** Both *** N-R R Both N-R R Both CASBEE / Y 2010 / / Y / Y / Green Globes / / 2014 / / Y / / / Built Green / / / / / / / 2014 / 5(5) 1(1) 2(2) 2(1) 2(2) 1(1) Green Star / / / / / / 2009 / / NABERS / / / / / / 2010 Y / Home Star / / / / / / / 2014 / 3(3) 2(2) 2(1) 20XX: Year of resource's most recent update Key countries Japan China Canada No. Americas (Reviewed) Australia Australia New Zealand No. Oceania Within a scheme, several major categories are used for the evaluation, such as water efficiency, energy, and IEQ. This study focuses on the IAQ section, which includes the sources and species of indoor air pollutants, as well as methods that can be applied to maintain high IAQ. The IAQ section is typically included within the IEQ category, or sometimes in the health and well-being category. Related sections in green building IEQ schemes, such as thermal comfort, acoustic performance, and lighting/views, are not included in this study. 2.3 Scheme review method A total of 55 schemes were considered for the detailed review. There are two steps in the review procedure, as shown in Figure 2. In step 1, the objectives are to analyze how and to what extent IAQ is taken into account in green building certifications. IAQ sections and rating systems in green building schemes were reviewed. A statistical analysis was performed to quantitatively analyze the contribution of IAQ in green building certifications, as well as the target indoor air pollutants and the methods that are commonly employed for IAQ management. For certifications that have more than one scheme for different types of buildings, an average value is used to represent the contribution of IAQ. To analyze indoor air pollutants and IAQ management in different schemes within a certification, all the pollutants listed in the different schemes are combined, yielding the most comprehensive coverage of indoor air pollutants considered within GB/T 50378 Canada (Reviewed) the certification. In step 2, detailed analysis focuses on IAQ management. Methods and standards
	Egypt were reviewed to analyze the requirements for controlling the emission sources of indoor air GPRS / / 2011 / / / / / /
	No. of pollutants, as well as those for ventilation and indoor air measurement. For certifications with No. of No. of No. Africa 1(1) 1(1)
	countries/regions more than one scheme for different types of buildings, all the IAQ management methods are certifications schemes (Reviewed)
	SUM	Asia	13	11(1	13	30
		31(31)	9(9) 8(7)	5(4) 4(3) 8(5) 6(6) 9(6)	4(4)
	(Reviewed)	Europe	9	1)	9	14
	Americas * N-R: Non-residential buildings	5		5	7
	Oceania ** R: Residential buildings	2		3	3
		Africa	1		1	1
	SUM *** Both: Both non-residential and residential buildings 30	31	55
	/: Resource not found
	Y: Resource found but not accessible (e.g., not free of charge)

Figure 1. Green building certifications worldwide 2.

2 Green building schemes

A green building scheme is a method used to evaluate sustainability during construction and/or throughout a building's life-cycle. Some certifications include different schemes designed to certify different types of buildings for design and/or performance. Two general methods are used to classify buildings into different types. One method is to classify buildings into two major categories, i.e., new buildings and existing buildings. New buildings include buildings that are under design, under construction, or recently completed. Existing buildings include buildings that are fully built, under repair, or under renovation. The other classification method categorizes buildings into non-residential and residential buildings. Non-residential buildings include offices, shopping malls, schools, etc. Residential buildings include apartments and houses. By combining the two methods, there are nine possible considered together when discussing the methods used to maintain high IAQ.

  Indoor air pollutants in green building certifications A statistical analysis was performed to summarize the indoor air pollutants that are taken into account in green building certifications worldwide, as shown in Figure4. In three certifications (EEWH, Protocollo ITACA, and Home Star), no specific indoor air pollutant is targeted. The top 3 indoor air pollutants that are most frequently considered worldwide are VOCs, formaldehyde, Frequency of indoor air pollutants in green building certifications worldwide Green building certifications in Europe, Asia, Americas, Oceania, and Africa place different amounts of emphasis on target indoor air pollutants. Figure5shows the indoor air pollutants considered in green building certifications by continent. Among chemical pollutants, 80% of the green building certifications in Americas consider formaldehyde as a target indoor air pollutant, compared with 44% in Europe. A total of 44% of the green building certifications in Europe are interested in indoor total VOC (TVOC) concentrations, compared with 15% in Asia. Ozone is not mentioned in certifications in Oceania or Africa. Semi-volatile organic compounds (SVOCs) are only mentioned in the KLIMA certification in Austria. Asbestos is taken into account in 56% of the European certifications, compared with 25% in Oceania and Africa. Radon is not considered in Oceania or Africa. Finally, regarding biological contamination, green building certifications in Oceania and Africa, as well as in Asia, pay more attention to indoor microbes (50% and 38%, respectively) compared with the certifications in Europe and Americas (22% and 20%, respectively).To manage IAQ, three pathways are preferred in green building schemes, i.e., emission source control, ventilation, and indoor air measurement. The three pathways focus on different periods of a building's life-cycle. Emission source control aims at designing and choosing low-emission indoor materials, e.g., paint, carpets and flooring, and furniture, for indoor construction and renovation. The goal of ventilation is to provide an appropriate indoor/outdoor air exchange rate to maintain high IAQ. Indoor air measurement is used to check whether indoor concentrations comply with given thresholds and thus to monitor the efficiency of emission source control methods and ventilation. Indoor air measurement can take place in new buildings before or after indoor occupancy. The pollutants measured include chemical pollutants and particulate matter.

			90%
			80%
	30% 40% 50% 60% 70% 3.3 IAQ management Frequency
	25% 50% 75% 100% Figure 4. 0% Frequency	0% 20% Formaldehyde 10% Asia Europe America Oceania & Africa Ozone	Frequency	50% 0% 10% 20% 30% 40%	TVOC Asia Europe America Oceania & Africa Asbestos
	Frequency	0% 3% 6% 9% 12% 15% 21% 18%		Frequency	0% 60% 20% 40%
			Asia Europe America Oceania			Asia Europe America Oceania
			& Africa			& Africa
			Carbon dioxide			Particles
	Frequency	0% 20% 40% 60% 80% 100%		Frequency	30% 6% 12% 18% 24%
			Asia Europe America Oceania		0%
			&			Asia Europe America Oceania
			Africa			& Africa
	building schemes. Such third-party certifications are usually national certifications; acceptable
			Radon			Microbes
	25% third-party certifications vary widely among different green building certifications. For the 60%
	0% 5% 10% 15% 20% alternative option, materials or products must have VOC contents achieving the threshold level Frequency 0% 15% 30% 45% Frequency mentioned in the green building schemes, as shown in Table 4, or of compliance with other
	Asia Europe America Oceania & Africa emissions and content standards such as European Directive 2004/42/CE: 2004 and Asia Europe America Oceania & Africa
		Figure 5. Frequency of target indoor pollutants in certifications by continent
			20

*** Both: Both non-residential and residential buildings 3.2 and carbon dioxide (CO2). VOCs are taken into account in 26 (84%) of the green building certifications. In 21 certifications, VOCs are used to represent indoor chemical pollutants in general, and no specific compounds are identified in the category. In 5 certifications (CASBEE, LEED, GB/T 50378, HQE, and IGBC), VOC species are listed in detail, including compounds such as benzene and toluene. CO2 is considered an indoor pollutant in 65% of the certifications.

Asbestos pollution is taken into account in 45% of the certifications, not only for existing buildings but also for new construction. Microbes, such as fungi and bacteria, are considered in 32% of the certifications. The control of indoor airborne particle (PM10 or PM2.5) concentrations is proposed in 16% of the certifications.

The occurrence frequencies of the three pathways proposed in green building certifications are shown in Figure

6

. All of the certifications propose ventilation for IAQ management, whereas 77% and 65% of the certifications propose emission source control and indoor air measurement, respectively. Certifications in Asian and American countries typically include emission source control requirements. Indoor air measurement is most commonly proposed in European and American certifications. Figure

6

. IAQ management in green building certifications

3.3.1 Emission source control of indoor pollutants

Emission source control of indoor pollutants, proposed in 77% of the certifications, aims at designing and choosing low-emission materials. For paint and carpets, the target pollutants are mainly VOCs. There are two options that allow building materials to be considered low-VOCemission materials in green building schemes. For the first option, materials must have thirdparty green material certifications to be considered low-VOC-emission materials in green ANSI/BIFMA e3-2011. Low-formaldehyde-emission products are recommended in green building schemes for wooden materials, such as medium-density board, wooden flooring, etc.

Table 4 .

 4 Threshold level of VOC contents in building materials (g/L)

	IGBC	Pearl	Trees

requirements for ventilation vary greatly among different schemes. International standards are commonly referenced in green building schemes. As shown in Figure

7

, 39% of the green building certifications examined here preferentially use the ASHRAE 62.1 standard to specify minimum ventilation rates. A total of of the green building certifications, mostly in European countries, rely on EN 15251 and EN 13779 standards. Other certifications, such as Green Star and Green Mark, use local ventilation standards for the design of ventilation.

Table 6 .

 6 Indoor air sampling strategies in certifications for which detailed information is

	provided

Table 7 .

 7 Standards and methods used to measure indoor formaldehyde and TVOC concentrations

	Pollutant	ISO 16000-3 ISO 16000-6 GB/T 18883 Other protocols
	Formaldehyde LEED	/	GB/T 50378 HQE: HQE Performance
		BREEAM		Working Group;
		DGNB		KLIMA: ISO 16000-2 & EN
		IGBC		717-1;
		NABERS		GPR: Not mentioned;
				NABERS: By accredited
				assessor.
	TVOC		LEED	GB/T 50378 HQE: HQE Performance
			BREEAM	Working Group;
			DGNB	KLIMA: ISO 16000-5 &
			IGBC	ONORM M 5700-2;
				NABERS: ISO 16200-1, by
				accredited assessor.
	Measured indoor air pollutant concentrations are usually compared with threshold values. The
	ranges of these concentration thresholds reported in the considered green building schemes are
	shown in

Table 8 .

 8 The concentration thresholds of indoor air pollutants may vary among certifications according to different rating points (DGNB) or exposure times (HQE). According

Table 8 .

 8 Concentration thresholds of indoor air pollutants used in green building certifications

	Pollutant	Threshold range	Certification
	Formaldehyde	10 -120 µg/m 3	IGBC, HQE, BREEAM, DGNB, KLIMA,
			LEED, NABERS
	TVOC	300 -25000 µg/m 3	IGBC, HQE, BREEAM, DGNB, KLIMA,
			LEED, NABERS
	Benzene	2 -5 µg/m 3	HQE
	PM10	20 -50 µg/m 3	IGBC, HQE, LEED, NABERS
	PM2.5	10 -25 µg/m 3	HQE, LEED
	CO2	530 -1500 ppm	GREENSHIP, IGBC, Pearl, KLIMA,
			GPRS, NABERS
	CO	10 -100000 µg/m 3	GREENSHIP, IGBC, HQE, NABERS
		exposure per 8 hours,
		or +2 ppm over outside
	NO2	40 -5600 µg/m 3	GREENSHIP, HQE

Acknowledgements

The authors thank Dr. Vyt Garnys for his comments on the manuscript.


Wenjuan Wei
email: wenjuan.wei@cstb.fr

Olivier Ramalho

Corinne Mandin

A long-term dynamic model for predicting the concentration of semivolatile organic compounds in indoor environments: application to phthalates

Keywords: SVOC, phthalate, emission, partition, building material, indoor air quality

Semivolatile organic compounds (SVOCs) in indoor environments can partition into the gas phase, airborne particles, and settled dust and onto available surfaces. A long-term dynamic model was developed to predict the hourly concentrations of SVOCs over a year in the gas phase, airborne particles, and settled dust and on each sink surface. The model takes into account mass transfer mechanisms, the reactivity of SVOCs with oxidants indoors, and the influence of four indoor environmental factors (the air temperature, relative humidity, concentration of indoor airborne particles, and air exchange rate) on the mass transfer parameters. The model was validated for DEHP (di-2-ethylhexyl phthalate) and BBzP (butyl benzyl phthalate) by comparing the predicted concentrations in all the phases with the measured concentrations obtained in an environmental chamber and a test house. The model was then used to predict the hourly averaged concentration of BBzP in all the phases under real environmental conditions over a year. More than 52% of the variance in the BBzP concentration was found to be associated with the covariance of the environmental factors. The air exchange rate contributed to 16% of the variance in the concentration. In addition, the indoor air temperature and relative humidity contributed 9% of the variance in the gas-phase concentration of BBzP and 7% of the variance in the settled dust concentration of BBzP. The variance in the concentration of the total suspended particles contributed 10% of the variance in the BBzP concentration on the walls and windows.

INTRODUCTION

Semivolatile organic compounds (SVOCs), such as phthalates, flame retardants, pesticides, and polycyclic aromatic hydrocarbons, may originate from both indoor and outdoor sources and partition in indoor environments among the gas phase, airborne particles, settled dust, and available surfaces [START_REF] Weschler | Semivolatile organic compounds in indoor environments[END_REF]. Consequently, occupants can be exposed indoors to SVOCs through multiple pathways such as inhalation [START_REF] Liu | Exposure to SVOCs from inhaled particles: the impact of desorption[END_REF], dermal uptake [START_REF] Weschler | Transdermal uptake of diethyl phthalate and di(n-butyl) phthalate directly from air: Experimental verification[END_REF], and ingestion of settled dust [START_REF] Tajima | Detection and intake assessment of organophosphate flame retardants in house dust in Japanese dwellings[END_REF]. To evaluate the health risk associated with indoor exposure to SVOCs, the SVOC concentrations need to be either measured in all the phases or estimated by modeling.

Several studies have been carried out to address the mass transfer mechanism of SVOCs in indoor environments [START_REF] Wu | Adsorption of Phthalates on Impervious Indoor Surfaces[END_REF][START_REF] Weschler | Growth of organic films on indoor surfaces[END_REF][START_REF] Morrison | Partitioning of PCBs from air to clothing materials in a Danish apartment[END_REF][START_REF] Cao | A SPME-based method for rapidly and accurately measuring the characteristic parameter for DEHP emitted from PVC floorings[END_REF], and fugacity-based models have been developed to predict indoor SVOC concentrations [START_REF] Bennett | Fugacity-Based Indoor Residential Pesticide Fate Model[END_REF][START_REF] Shin | Intake fraction for the indoor environment: A tool for prioritizing indoor chemical sources[END_REF][START_REF] Zhang | Multimedia modeling of polybrominated diphenyl ether emissions and fate indoors[END_REF]. The first dynamic model was developed to predict the emission of phthalates from a piece of vinyl flooring into the gas phase and the mass transfer of phthalates between the gas phase and airborne particles in a single room [START_REF] Xu | Predicting emissions of SVOCs from polymeric materials and their interaction with airborne particles[END_REF]. The phthalate concentrations in both the gas phase and airborne particles were predicted. The settled dust and several sink surfaces, e.g., window and human skin, were then added to the model, and the model was extended from a single room to two adjacent rooms [START_REF] Xu | Predicting residential exposure to phthalate plasticizer emitted from vinyl flooring: A mechanistic analysis[END_REF]. The SVOC concentrations in the gas phase, airborne particles, settled dust, and on each sink surface were predicted. Later, the model was improved by considering the deposition of airborne particles, the resuspension of settled dust [START_REF] Liu | The influence of aerosol dynamics on indoor exposure to airborne DEHP[END_REF][START_REF] Shi | Modeled exposure assessment via inhalation and dermal pathways to airborne semivolatile organic compounds (SVOCs) in residences[END_REF], and the reactivity of SVOCs with hydroxyl radicals, nitrate radicals, and ozone [START_REF] Wei | Reactivity of semivolatile organic compounds with hydroxyl radicals, nitrate radicals, and ozone in indoor air[END_REF]. For the prediction of SVOC concentrations for a large dataset of buildings, a probabilistic approach based on Monte Carlo simulation was developed to predict the distribution of the SVOC concentrations under equilibrium conditions [START_REF] Wei | Predicting the gas-phase concentration of semi-volatile organic compounds from airborne particles: Application to a French nationwide survey[END_REF].

Environmental factors, e.g., indoor air temperature, relative humidity, the concentration of airborne particles, and the air exchange rate, have a significant influence on mass transfer parameters such as mass transfer coefficients and partition coefficients [START_REF] Wei | Influence of indoor environmental factors on mass transfer parameters and concentrations of semi-volatile organic compounds[END_REF]. To use modeling approaches with real environmental conditions, the impact of the environmental factors on the mass transfer parameters needs to be integrated into the equations of the models and quantified at each time step of the calculation.

Therefore, the objective of this study is to develop a dynamic model to predict the concentration of SVOCs in real indoor environments over long periods. To reach this objective, three aspects should be considered while developing a model: [START_REF] Weschler | Semivolatile organic compounds in indoor environments[END_REF] the model should include the emission of SVOCs from multiple surface sources and the sorption of SVOCs onto multiple sink materials; [START_REF] Liu | Exposure to SVOCs from inhaled particles: the impact of desorption[END_REF] the model should include the mass transfer mechanisms of SVOCs, the deposition and resuspension of particles, and the reactivity of SVOCs; and (3) the model should address the impact of environmental factors on the mass transfer parameters and concentrations of SVOCs at each time step of the calculation.

MATERIAL AND METHODS

Development of the model

To predict SVOC concentrations in indoor environments, the following mechanisms were considered in the model (Fig. 1): (1) the continuous emission of SVOCs from indoor surfaces to the gas phase; (2) the mass transfer of SVOCs among the gas phase, airborne particles, settled dust, and sink surfaces; (3) the transport of SVOCs between indoor and outdoor environments in the gas phase, airborne particles, and settled dust; (4) the gas-and particle-phase reaction of SVOCs with oxidants indoors; and (5) the deposition of airborne particles onto floor dust and other surfaces (e.g., furniture) and the resuspension of the dust into the air. To fully address the mass transfer processes of SVOCs in a room for a robust prediction of SVOC concentrations, the model is currently based on a single-room environment, and it will be extended to a multiroom environment in the future.

where Cg (µg/m 3 ), Cp (µg/m 3 ), Cd (µg/g), and Cs (µg/m 2 ) are the concentrations of the compound in the gas-phase, airborne particles, settled dust on the floor, and sink surfaces in the room, respectively; t (h) is time, Va (m 3 ) is the volume of the room; hme, hmp, hmd, and hms (m/h) are the mass transfer coefficients in the boundary layer of the source surfaces, airborne particles, settled dust, and sink surfaces, respectively; Ae, Ap, Ad, and As (m 2 ) are the areas of the source surfaces, airborne particles, settled dust on the floor, and sink surfaces, respectively; y0 (µg/m 3 ) is the gasphase concentration adjacent to the source surface; and TSP (µg/m 3 ) is the concentration of the total suspended particles in indoor air. TSP is related to indoor/outdoor particle transport, particle dynamics indoors, and indoor particle emission. Indoor particle emission is influenced by human activities such as cooking and cleaning. No model can fully address the indoor particle concentration unless a scenario is defined with scheduled activity of particle sources and changes in window openings. Therefore, instead of calculating the indoor particle concentration using a particle mass balance equation under a particular activity scenario, the current model requires the indoor particle concentration as an input. This input can be constant or time dependent and can be measured or predicted from other particle transport models. Kp (m 3 /µg), Kd (m 3 /g), and Ks (m) are the particle/gas, dust/gas, and sink/gas partition coefficients, respectively; Cgin (µg/m 3 ) is the outdoor gas-phase concentration of the compound with a transfer efficiency assumed to be equal to one; Q (m 3 /h) is the air flow rate; and k1g (h -1 ) is the pseudo-first-order reaction rate constant in the gas phase. The model refers to the emission of SVOCs from multiple sources, the sorption of SVOCs onto multiple sink surfaces, and the reaction of SVOCs with multiple oxidants. The subscripts, i, j, and x, represent the multiple sources, sinks, and oxidants (e.g., hydroxyl radicals, nitrate radicals, and ozone). Eq. ( 1) considers the continuous emission of a compound from source surfaces, while the emission from intermittent sources is not considered in the current model. The sink surfaces are assumed to be impermeable [START_REF] Weschler | Growth of organic films on indoor surfaces[END_REF][START_REF] Liang | Measuring and modeling surface sorption dynamics of organophosphate flame retardants on impervious surfaces[END_REF]. Therefore, SVOCs can form an organic film on the sink surface, and the diffusion of SVOCs through the material is neglected. Some recent studies have observed the mass transfer of SVOCs between source materials and settled dust in direct contact [START_REF] Liagkouridis | Mass transfer of an organophosphate flame retardant between product source and dust in direct contact[END_REF][START_REF] Sukiene | Direct and air-mediated transfer of labeled SVOCs from indoor sources to dust[END_REF]. However, this process is not taken into account in the current model.

where vdep (m/h) is the deposition velocity of airborne particles of all sizes; Addep and Asdep (m 2 ) are the deposition areas of the floor dust and other surfaces; and Rsus (h -1 ) is the resuspension rate of the deposited particles of all sizes. vdep is associated with the type of surface and particle size distribution. However, there is insufficient information in the literature addressing the sizedependent particle deposition velocity for each type of indoor surface. Therefore, the current model uses an identical value for all surfaces for practical reasons. To include particle size effects in the model, the size distribution of indoor airborne particles and its changes over time need to be defined. Studies on the daily change of the indoor particle size distribution are rare. Therefore, the current model focuses on indoor PM10 for simplicity. The vdep (1.1 m/h) and Rsus (2.4×10 -5 h -1 ) values were retrieved from the literature [START_REF] Liu | The influence of aerosol dynamics on indoor exposure to airborne DEHP[END_REF][START_REF] Shi | Modeled exposure assessment via inhalation and dermal pathways to airborne semivolatile organic compounds (SVOCs) in residences[END_REF]. The present model separates the floor dust from dust settled on other surfaces. Due to the large number of indoor surfaces, it is not feasible to model the dust concentration of SVOCs on each surface. In a normally cleaned room, a very thin layer of dust may exist on a surface. The dust concentration is associated with the surface concentration of SVOCs.

Therefore, the present model assumes that the dust concentration on a sink surface (Cd,j) is equal to the surface concentration (Cs,j) for simplicity. ρd (g/m 3 ) is the density of the settled dust, and Vdsus (m 3 )

is the volume of the floor dust that may resuspend. Dust mass loading is assumed to be constant.

Assus (m 2 ) is the area of the other surfaces where deposited particles may resuspend. Since deposited particles on a surface can also resuspend, Assus,j is assumed to be equal to Asdep,j. Cpin (µg/m 3 ) is the outdoor particle-phase concentration of the compound with a transfer efficiency assumed to be equal to one, and k1p (h -1 ) is the pseudo-first-order reaction rate constant of the compound in the particle phase.

The average SVOC concentration in the floor settled dust of all sizes without taking into account possible SVOC mass transfer between the source flooring and dust in direct contact is described by

d𝐶 d d𝑡 𝜌 d 𝑉 d = ℎ md 𝐴 d (𝐶 g - 𝐶 d 𝐾 d ) + 𝐶 p 𝑣 dep 𝐴 ddep -𝑅 sus 𝐶 d 𝜌 d 𝑉 dsus -∑ 𝑘 1d,𝑥 𝐶 d 𝜌 d 𝑉 d 𝑥 + 𝑞 din 𝜌 din 𝐶 din -𝑞 dout 𝜌 d 𝐶 d (3)
where k1d (h -1 ) is the pseudo-first-order reaction rate constant in the settled dust; Vd (m 3 ) is the volume of the floor dust; qdin and qdout (m 3 /h) are the flow rates of the dust entering and leaving the room, respectively; ρdin (g/m 3 ) is the density of the dust entering the room; and Cdin (µg/g) is the concentration of the compound in the dust coming from outdoors. Due to the difficulty in assessing it, the transport of settled dust between the indoor and outdoor environments was not considered in the present study. Therefore, the flow rates (qdin and qdout) were assumed to be equal to zero, and the volume of the floor dust was assumed to be constant.

The concentration of the compound on a sink surface is described by

d𝐶 s,
where k1s (h -1 ) is the pseudo-first-order reaction rate constant on the surface.

The mass transfer parameters in the model were retrieved from measured values in the literature or estimated using equations developed in previous studies. Direct measurements of y0 for phthalates have been carried out for various floorings [START_REF] Cao | A SPME-based method for rapidly and accurately measuring the characteristic parameter for DEHP emitted from PVC floorings[END_REF][START_REF] Xu | Measuring and predicting the emission rate of phthalate plasticizer from vinyl flooring in a specially-designed chamber[END_REF] and mattresses [START_REF] Liang | Emission of phthalates and phthalate alternatives from vinyl flooring and crib mattress covers: The influence of temperature[END_REF]. For phosphorous and brominated flame retardants, the concentrations in indoor air were measured when computers and televisions were present in the room [START_REF] Guo | Polybrominated diphenyl ethers in indoor air during waste TV recycling process[END_REF][START_REF] Saito | Indoor organophosphate and polybrominated flame retardants in Tokyo[END_REF]. Information on SVOC emissions from other indoor sources is not available in the literature. The mass transfer coefficients [START_REF] Deng | An analytical model for VOCs emission from dry building materials[END_REF][START_REF] Shi | Estimating indoor semi-volatile organic compounds (SVOCs) associated with settled dust by an integrated kinetic model accounting for aerosol dynamics[END_REF], partition coefficients [START_REF] Weschler | Growth of organic films on indoor surfaces[END_REF][START_REF] Wei | Distributions of the particle/gas and dust/gas partition coefficients for seventytwo semi-volatile organic compounds in indoor environment[END_REF] and reaction rate constants [START_REF] Wei | Reactivity of semivolatile organic compounds with hydroxyl radicals, nitrate radicals, and ozone in indoor air[END_REF] can be calculated using methods developed in previous studies.

Eqs. (1 -4) can be transferred into a system of m (m = j + 3) linear equations using the finite difference method. To ensure the stability and convergence of the solution, the backward difference method was used in the model.

𝐀𝐱 = 𝐛 (5)

where A is an m × m matrix, x is a column vector with m concentrations (Cg, Cp, Cd, and Cs for each of the j surfaces) and b is a column vector with m entries.

⋮ ⋮ ⋮ ⋮ ⋱ ⋮ 𝑎 𝑚1 𝑎 𝑚2 𝑎 𝑚3 𝑎 𝑚4 ⋯ 𝑎 𝑚𝑚 ] , 𝐱 = [ 𝐶 g 𝐶 p 𝐶 d 𝐶 s,1 ⋮ 𝐶 s,𝑗 ] , 𝐛 = [ 𝑏 1 𝑏 2 𝑏 3 𝑏 4 ⋮ 𝑏 m ]
The entries in matrix A and vector b are functions of (1) the geometry and air flow rate of the room, (2) the mass transfer parameters, (3) the surface of the source/sink materials, (4) the concentration of the total suspended particles, and (5) the density of settled dust. Detailed information on the entries of the matrix A and vector b is provided in the supporting information (SI). The values of model parameters are provided in Table S1 in the SI.

The indoor temperature (T), relative humidity (RH), air exchange rate (AER), and airborne particle concentration (TSP) can influence the mass transfer parameters and concentrations of SVOCs (Fig. 2). The impacts of the four environmental factors are not negligible and have been quantitatively addressed elsewhere [START_REF] Wei | Influence of indoor environmental factors on mass transfer parameters and concentrations of semi-volatile organic compounds[END_REF]. The impacts of T, RH, AER, and TSP were addressed quantitatively in the calculation of the mass transfer parameters in the model, e.g., y0, mass transfer coefficients, and partition coefficients, using equations presented in the literature [START_REF] Wei | Influence of indoor environmental factors on mass transfer parameters and concentrations of semi-volatile organic compounds[END_REF]. For each time step, the environmental factors were assumed to affect the mass transfer parameters without delay.

The model was coded in C# language using Visual Studio 2015 (Microsoft Visual Studio

Community 2015, version 14.0, 2016 Microsoft Corporation). A user-friendly interface was designed for nonprofessionals for the modeling of indoor SVOC concentrations (Fig. S1 in the SI).

The total calculation time was set to 365 days to address concentrations over a long period that included all the seasons. The time step was set to 1 h by default and should not be reduced, because the environmental factors were assumed to affect the mass transfer parameters immediately. For example, the temperature on the source surface changes with the air temperature at each time step and affects the emission without delay. These values can be changed to adapt to special needs. The input data to initiate the calculation of the model include ( 1

Validation of the model

Three predictions were performed to validate the model and to perform long-term dynamic predictions under real environmental conditions.

First, a validation of the model was carried out for di-2-ethylhexyl phthalate (DEHP) in a 2-L sandwich-like environmental chamber [START_REF] Xu | Measuring and predicting the emission rate of phthalate plasticizer from vinyl flooring in a specially-designed chamber[END_REF]. DEHP was emitted from a piece of vinyl flooring inside the chamber without the presence of airborne particles or settled dust. DEHP was measured in the chamber gas phase and was also absorbed on the surface of the chamber. All the environmental conditions remained constant during the duration of the experiment. The parameters for the model prediction (geometric parameters of the environmental chamber and the source material, source emission parameters, mass transfer coefficients, and partition coefficients) were retrieved from the measurement study [START_REF] Xu | Measuring and predicting the emission rate of phthalate plasticizer from vinyl flooring in a specially-designed chamber[END_REF], and the predicted hourly average concentrations were compared with the measured values.

Second, a validation of the model was performed for butyl benzyl phthalate (BBzP) measured in a 250-m 3 test house [START_REF] Bi | Fate and Transport of Phthalates in Indoor Environments and the Influence of Temperature: A Case Study in a Test House[END_REF]. BBzP was emitted from the flooring of the test house. BBzP was measured in both the gas and airborne particles in the indoor air, settled dust, and on the walls (measured on wooden surfaces representing walls, ceilings and furniture) and windows of the house. The environmental factors (T, RH, and AER) were changed 4 times over a period of less than 200 days in total. The TSP remained constant (4.0 ± 3.8 µg/m 3 ) over the period of study. The parameters for the model prediction (geometric parameters of the test house and the source material, source emission parameters, mass transfer coefficients, partition coefficients, and environmental parameters of the test house) were retrieved from a measurement study [START_REF] Bi | Fate and Transport of Phthalates in Indoor Environments and the Influence of Temperature: A Case Study in a Test House[END_REF], and the predicted hourly average concentrations were compared with the measured values.

Application of the model: a case study

The model was used to predict the BBzP concentrations under real indoor environmental conditions. Indoor temperature, RH, AER, and PM10 concentration were measured over a year (January 1-December 31, 2014) during a French study in a mechanically ventilated office [START_REF] Ramalho | Real time monitoring of indoor air quality in offices -source contributions and forecasting model[END_REF][START_REF] Ouaret | Indoor air pollutant sources using blind source separation methods[END_REF] and used in the test house experiment. The hourly average values of the environmental parameters in the office were the entry data for the model (Figs. S2-S5 in the SI). The PM10 concentration was used as the estimate of TSP. The hourly average AER was estimated from CO2 monitoring during the decay periods according to the method developed by Ramalho et al. [START_REF] Ramalho | Air stuffiness and air exchange rate in French schools and day-care centres[END_REF]. The other geometry and material emission parameters were those from the abovementioned test house. The hourly average concentrations of BBzP over a year were predicted considering two cases. For the first case, the initial BBzP concentrations in all the phases were assumed to be zero. This case corresponded to the prediction in a newly built room. The dynamic concentrations were calculated when the hourly average values of the environmental factors were used. In addition, the steadystate concentrations were calculated with the yearly-average values of the environmental factors.

For the second case, the initial BBzP concentration in all the phases was assumed to have reached the steady state that had been determined during the calculation of the first case. This case corresponded to a prediction in an existing room, and the hourly average concentrations were calculated for a period of a year. The contribution of each environmental factor to the variance in the BBzP concentration in each phase was estimated using the following equation. due to the covariance of all four environmental factors.

RESULTS AND DISCUSSION

Validation of the model

The predicted DEHP concentrations in both the gas phase and on the surface of the sandwich-like chamber were compared with the measured values (Fig. 3). Since the environmental factors on the walls, and on the windows. Measured data from [START_REF] Bi | Fate and Transport of Phthalates in Indoor Environments and the Influence of Temperature: A Case Study in a Test House[END_REF].

The comparisons of the environmental chamber and the test house results suggest that the model can provide robust estimates of the concentrations of the two phthalates in under both constant and dynamic environmental conditions. The pseudo-first-order reaction rate constants of DEHP and BBzP are much lower than the AER (25 h -1 in the environmental chamber, and between 0.5 and 0.71 h -1 in the test house), e.g., for the reaction with the hydroxyl radical in the gas phase, the k1g is between 5.1×10 -3 and 1.4×10 -1 h -1 for DEHP and between 2.6×10 -3 and 7.2×10 -2 h -1 for BBzP) [START_REF] Wei | Reactivity of semivolatile organic compounds with hydroxyl radicals, nitrate radicals, and ozone in indoor air[END_REF]. Therefore, the reactivity of the two phthalates does not have significant influence on their concentrations indoors. According to a detailed study of SVOC reactivity, reactivity plays an important role in the fate of indoor SVOCs for a number of polycyclic aromatic hydrocarbons (PAHs) and pesticides, such as benzo[a]anthracene, chrysene, benzo[b]fluoranthene, pyrene, diazinon, chlorpyrifos, and aldrin [START_REF] Wei | Reactivity of semivolatile organic compounds with hydroxyl radicals, nitrate radicals, and ozone in indoor air[END_REF].

Over a period of less than 200 days in the test house, the indoor air temperature (between 21 and 30 °C) and RH (between 24.9% and 40.4%) were changed four times. The AER (between 0.5 and 0.71 h -1 ) was changed 3 times. The experimental pattern of the variation in T, RH, TSP, and AER in this study cannot represent real environmental conditions, which have rapider changes. To validate the model in an ordinary room over a long period of time, future studies should measure SVOC concentrations in the gas phase, airborne particles, and settled dust and on indoor surfaces regularly. During the measurement period, indoor environmental factors should be monitored.

Dynamic modeling over a year

The hourly average concentrations of BBzP under the real environmental conditions of the French office study and considering the case of a newly built room are shown in Figs. 5 and6. The modeled concentration profiles considering an existing room are shown in Figs. S6 and S7 in the SI. The distribution of the BBzP concentrations over a year is shown in Table 1. Due to the variation in the environmental factors, the concentrations of BBzP in all the phases vary by approximately one order of magnitude over a year. In the existing room, the BBzP concentrations vary between 4 and 1.2 × 10 3 ng/m 3 for Cg, between 7.8 × 10 -4 and 3.1 × 10 1 ng/m 3 for Cp, between 3 and 7.1 × 10 2 µg/g for Cd, between 5.7 × 10 -4 and 2.7 × 10 1 µg/m 2 for Cs on the walls, and between 5.7 × 10 -4 and 2.6 × 10 1 µg/m 2 for Cs on the windows. Student's t-tests were performed to test the significance of the difference between the concentrations over the period of the predictions due to the difference in the initial concentrations. The p-values for Cg (0.51), Cp (0.75),

and Cd (0.46) are higher than 0.05, indicating that the initial BBzP concentrations have nonsignificant influences on the profiles of Cg, Cp, and Cd over a year. The p-values for Cs for the walls and windows are less than 0.05, suggesting that the Cs profiles of the two prediction cases are significantly different (Fig. S8 in the SI). A possible explanation is that BBzP is slowly forming an organic layer on the surface of the walls and windows [START_REF] Weschler | Growth of organic films on indoor surfaces[END_REF]. Therefore, the initial mass transfer processes for Cs, which is associated with the initial concentrations, take longer than those for Cg, Cp, and Cd. Correlation tests show that the values of Cg and Cp (r = 0.86) as well as the BBzP concentrations on the two types of sink surfaces (r > 0.999) are highly correlated regardless of the initial concentrations used for the prediction (Fig. S9 in the SI). The environmental factors have combined effects on the mass transfer parameters (Fig. S10 in the SI) and concentrations (Fig. S11 in the SI). When the temperature increases, all concentrations increase because of the increasing y0 [START_REF] Cao | A SPME-based method for rapidly and accurately measuring the characteristic parameter for DEHP emitted from PVC floorings[END_REF][START_REF] Liang | Emission of phthalates and phthalate alternatives from vinyl flooring and crib mattress covers: The influence of temperature[END_REF] and mass transfer coefficients [START_REF] Deng | An analytical model for VOCs emission from dry building materials[END_REF][START_REF] Holmgren | A generic emission model to predict release of organic substances from materials in consumer goods[END_REF] and the decreasing partition coefficients [START_REF] Arp | Evaluation of a predictive model for air/surface adsorption equilibrium constants and enthalpies[END_REF][START_REF] Goss | The Air/Surface Adsorption Equilibrium of Organic Compounds Under Ambient Conditions[END_REF][START_REF] Wei | Temperature dependence of the particle/gas partition coefficient: An application to predict indoor gas-phase concentrations of semi-volatile organic compounds[END_REF]. When the RH increases, Cp and Cd decrease because of the decreasing Kp and Kd values [START_REF] Jang | A thermodynamic approach for modeling partitioning of semivolatile organic compounds on atmospheric particulate matter: Humidity effects[END_REF][START_REF] Hippelein | Soil/Air Partitioning of Semivolatile Organic Compounds. 2. Influence of Temperature and Relative Humidity[END_REF]. The substrate of indoor settled dust includes soil, settled particles, human and animal dander, cloth fibers, and fungal material [START_REF] Cao | Mechanisms influencing the BFR distribution patterns in office dust and implications for estimating human exposure[END_REF][START_REF] Lioy | Dust: A metric for use in residential and building exposure assessment and source characterization[END_REF][START_REF] Maertens | The mutagenic hazards of settled house dust: A review[END_REF] and varies widely among indoor environments [START_REF] Rasmussen | A multi-element profile of house dust in relation to exterior dust and soils in the city of Ottawa, Canada[END_REF]. The impact of RH on Kd was available in the literature only for soil [START_REF] Wei | Influence of indoor environmental factors on mass transfer parameters and concentrations of semi-volatile organic compounds[END_REF][START_REF] Hippelein | Soil/Air Partitioning of Semivolatile Organic Compounds. 2. Influence of Temperature and Relative Humidity[END_REF]. No equation is available in the literature to quantitatively address the influence of RH on Ks. Therefore, this influence is not included in the current model. When the PM10 concentration increases, all concentrations increase because of the increasing mass transfer coefficients [START_REF] Liu | Role of aerosols in enhancing SVOC flux between air and indoor surfaces and its influence on exposure[END_REF][START_REF] Liu | The effect of ventilation on indoor exposure to semivolatile organic compounds[END_REF].

When the AER increases, all the concentrations decrease if other environmental factors remain unchanged. The contributions of the environmental factors to the variance in the SVOC concentrations were estimated using Eq. ( 6). To reduce the influence of the variance associated with the initial conditions and the initial mass transfer process, the analysis was carried out only for case 2 (Fig. 7). More than 52% of the variances in all the phases (60% for Cg, 82% for Cp, 52%

for Cd, 65% for Cs on the walls, and 64% for Cs on the windows) are associated with the covariances of the environmental factors, which cannot be separated. In addition, more than 16% of the variances in all the phases (27% for Cg, 16% for Cp, 36% for Cd, 19% for Cs on the walls, (

) 1
The model is currently developed for an unoccupied room. The influence of human activities, e.g., cooking and cleaning, on indoor environmental factors and SVOC concentrations has not been considered. Human activities may lead to the emission of particles and chemical compounds, resuspension of settle dust, and dust entry and removal.

(2)

The model does not consider SVOC emissions from intermittent sources. These sources include, e.g., the emissions of polyaromatic hydrocarbons due to cooking, the spray of synthetic musks and pesticides, and other punctual usage of products containing SVOCs.

(3)

The model considers indoor impermeable sink surfaces and does not take into account porous sink surfaces. Porous surfaces may lead to significant SVOC reservoirs and extend SVOC persistence in an indoor environment.

(4)

The model considers that the transport efficiency of SVOCs between indoor and outdoor environments equals one. In fact, this value may differ depending on the system of ventilation.

The model requires the concentration of total suspended particles as an input. This value currently comes from measurements or the output of other models. The current model does not predict the indoor concentration of the total suspended particles, regardless of their origins from indoor or outdoor sources.

(5)

The model predicts the average concentration of SVOC in airborne particles and settled dust for PM10. Recent studies have shown some effects of particle size distribution and age on indoor SVOC concentrations in different phases [START_REF] Cao | Indoor particle age, a new concept for improving the accuracy of estimating indoor airborne SVOC concentrations, and applications[END_REF]. These effects should be considered for further improvement of the model. For this purpose, the size distribution of indoor airborne particles and its changes over time need to be defined based on measurements or modeling approaches. Moreover, future studies should address the indoor particle size distribution and particle-related parameters, such as the partition coefficient, deposition velocity, and resuspension rate, in terms of the size effect.

CONCLUSIONS

A long-term dynamic model was developed to predict the concentrations of SVOCs in indoor environments. The model characterizes the emission of SVOCs from multiple source surfaces and the sorption of SVOCs onto multiple sink surfaces for the prediction of the SVOC concentrations in the gas phase, airborne particles, and settled dust and on each sink surface. The model takes into account the mass transfer mechanisms of SVOCs in an indoor environment, the possible contribution of the outdoor SVOC concentration when the transfer efficiency is assumed to be one, and the reactions of SVOCs with hydroxyl radicals, nitrate radicals, and ozone. The impacts of indoor air temperature, RH, the concentration of the total suspended particles, and the AER on the mass transfer parameters and SVOC concentrations are calculated quantitatively in each time step of the calculation. Therefore, the model can be applied to both environmental chambers under regulated environmental conditions and unoccupied rooms under real environmental conditions.

Fig. 1 .

 1 Fig. 1. Schematic of the model.

Fig. 2 .

 2 Fig. 2. Influence of environmental factors on the transport of SVOCs.

  Var(𝐶 𝑚 )| Total = Var(𝐶 𝑚 )| Var(𝑇) + Var(𝐶 𝑚 )| Var(𝑅𝐻) + Var(𝐶 𝑚 )| Var(𝑃𝑀10) + Var(𝐶 𝑚 )| Var(𝐴𝐸𝑅) ± Var(𝐶 𝑚 )| Cov(𝑇,𝑅𝐻,𝑃𝑀10,𝐴𝐸𝑅) (6) where Var(𝐶 𝑚 )| Var(𝑇,𝑅𝐻,𝑃𝑀10,𝐴𝐸𝑅) is the variance in the SVOC concentration (phase m); Var(𝐶 𝑚 )| Var(𝑇) , Var(𝐶 𝑚 )| Var(𝑅𝐻) , Var(𝐶 𝑚 )| Var(𝑃𝑀10) , and Var(𝐶 𝑚 )| Var(𝐴𝐸𝑅) are the variances in the SVOC concentration (phase m) due to the variance in the T, RH, PM10 concentration, and AER, respectively; and Var(𝐶 𝑚 )| Cov(𝑇,𝑅𝐻,𝑃𝑀10,𝐴𝐸𝑅) is the variance in the SVOC concentration (phase m)

Fig. 3 .Fig. 4 .

 34 Fig. 3. Hourly average concentration of DEHP in the sandwich-like chamber (a) in the gas phase

Fig. 5 .Fig. 6 .

 56 Fig. 5. Predicted hourly average BBzP concentrations in the gas phase (Cg) and airborne particles

Fig. 7 . 3 . 3 .

 733 Fig. 7. Contributions of the environmental factors to the variances in BBzP concentrations

  𝑗 d𝑡 𝐴 s,𝑗 = ℎ ms,𝑗 𝐴 s,𝑗 (𝐶 g -𝐶 s,𝑗 𝐾 s,𝑗 ) + 𝐶 p 𝑣 dep 𝐴 sdep,𝑗 -𝑅 sus 𝐶 s,𝑗 𝐴 ssus,𝑗 -∑ 𝑘 1s,𝑥 𝐶 s,𝑗 𝐴 s,𝑗 𝑥

  𝑎 11 𝑎 12 𝑎 13 𝑎 14 ⋯ 𝑎 1𝑚 𝑎 21 𝑎 22 𝑎 23 𝑎 24 ⋯ 𝑎 2𝑚 𝑎 31 𝑎 32 𝑎 33 𝑎 34 ⋯ 𝑎 3𝑚 𝑎 41 𝑎 42 𝑎 43 𝑎 44 ⋯ 𝑎 4𝑚

	𝐀 =
	[

Table 1 .

 1 Distribution of BBzP concentrations over a year

		P5	P25	P50	P75	P95	Yearly-	Standard
							average	deviation
	Newly built room
	In the gas phase (ng/m 3 )	59.2 116.7 175.9 240.3 382.9 191.6	108.9

ACKNOWLEDGMENTS

The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement n. PCOFUND-GA-2013-609102, through the PRESTIGE program coordinated by Campus France (PRESTIGE-2015-3-0016).