domain: chim sde

text:
Andre Estevez-Torres
email: andre.estevez-torres@sorbonne-universite.fr

Fabienne Gauffre

Guillaume Gouget

Chloé Grazon

Philippe Loubet
email: philippe.loubet@u-bordeaux.fr

Karine Ndiaye

Murielle Berlande

Karine Heuze

Pascale Godard

Valérie Ravaine

Laurent Jeanneau

Marianne De Paepe

Olivier Aumont

Jérôme Mariette

Elsa Fg

Olivier Caytan

Gwendal Jeannin

Pierrick Le Bars

Corinne Ménez

Karine Perier

Louise-Anne Robin

Rémi Cariou

Carbon footprint and mitigation strategies of three chemistry laboratories

Keywords: Sustainability, greenhouse gas, decarbonization, life cycle assessment, environment, sustainable research CF, Carbon Footprint, EF, Emission Factor, GHG, GreenHouse Gases, MS, Mitigation strategy, LCA, Life Cycle Assessment

As the global imperative for decarbonization gains momentum, the need for action in chemistry laboratories becomes increasingly apparent. This study examines the 2019 carbon footprint of three French chemistry laboratories encompassing energy, purchases, travels, and commutes. The average per capita carbon footprint stands at 5.6 teqCO2/year, positioning chemistry laboratories slightly above the median calculated across all disciplines. Key contributors are purchases (31-42%) and heating (23-33%), driven by fume hoods, heavy equipment and consumables. Attainable mitigations strategies suggest a 40-50% reduction by 2030. Pivotal efforts involve transitioning heating sources to renewables, extending equipment lifespan, collaborative resource management, as well as a limitation in the use of planes and thermic cars. Such changes imply actions at the level of the government, the university and the individual. We suggest fostering a sustainable research environment in chemistry laboratories by rationalizing experimental practices and dedicating time to consider the socio-environmental implications of research.

Introduction

Measurable proofs of the accumulation of carbon dioxide in the atmosphere and its relation with the combustion of fossil fuels for human activities were established by the chemist Charles Keeling, shortly before 1960. At the same period, the physicist Edwards Teller warned the leaders of the American Petroleum Industry against global warming and sea level rise. In addition, a report addressed in 1965 to the president Johnson by its Scientific Advisory Committee, predicted marked change in the climate by 2000. [START_REF] Franta | Early oil industry knowledge of CO2 and global warming[END_REF] Since then, scientists have achieved numerous measurements and models that leave no doubts about the urgency and seriousness of the situation that humanity faces. These works are used and made available to the public and policy-makers through the reports of the Intergovernmental Panel on Climate Change (IPCC). 2 Reducing greenhouse gas (GHG) emissions (and more broadly the environmental footprint) of research activity has gradually become a moral imperative and a credibility issue for the scientific community. Indeed, the academic world plays a major role in the production and dissemination of knowledge on the subject, in particular through the training of students. Scientists are also prompted to contribute to the public debate on climate change and mitigation issues, and their behavior in their professional, as well as personal life, is expected to be congruent with their message. 3 Many scientists have joined calls for urgent climate action, sometimes even through civil disobedience acts. 4 Since many countries have committed to reach carbon neutrality by 2050 through the Paris Climate Change Agreement, the transition to a less GHG-emitting way of doing research is also a strategic imperative. The sooner, the better. However, there are still few publications quantifying the GHG emissions of academic research activities. 5,6 Those that do exist often focus on the carbon footprint of large conferences or large facilities such as telescopes. [START_REF] Portegies Zwart | The ecological impact of high-performance computing in astrophysics[END_REF][START_REF] Klöwer | An analysis of ways to decarbonize conference travel after COVID-19[END_REF][START_REF] Jäckle | The Carbon Footprint of Travelling to International Academic Conferences and Options to Minimise It[END_REF][START_REF] Stevens | The imperative to reduce carbon emissions in astronomy[END_REF][START_REF] Aujoux | Estimating the carbon footprint of the GRAND project, a multi-decade astrophysics experiment[END_REF][START_REF] Burtscher | Forging a sustainable future for astronomy[END_REF][START_REF] Berné | The carbon footprint of scientific visibility[END_REF] A few studies on the perimeter of a laboratory or a university were also reported. [START_REF] Leon | Environmental assessment of four Basque University campuses using the NEST tool[END_REF][START_REF] Fry | Assessing carbon footprints of cities under limited information[END_REF][START_REF] Güereca | Carbon Footprint as a basis for a cleaner research institute in Mexico[END_REF][START_REF] Mariette | An open-source tool to assess the carbon footprint of research[END_REF][START_REF] Cooper | The Carbon Footprint of a UK Chemical Engineering Department -The Case of Imperial College London[END_REF][START_REF] Martin | A comprehensive assessment of the carbon footprint of an astronomical institute[END_REF][START_REF] Larsen | Investigating the Carbon Footprint of a University -The case of NTNU[END_REF] Even fewer publications propose reduction strategies. The most discussed aspect concerns air travel and international conferences, with the possibility to turn towards virtual events. [START_REF] Yates | Can virtual events achieve co-benefits for climate, participation, and satisfaction? Comparative evidence from five international Agriculture, Nutrition and Health Academy Week conferences[END_REF][START_REF] Tseng | Managing academic air travel emissions: Towards system-wide practice change[END_REF][START_REF] Reyes-García | Decarbonizing the academic sector: Lessons from an international research project[END_REF] A number of studies focus on the consumption of single-use plastics, [START_REF] Kilcoyne | Reducing environmental impacts of marine biotoxin monitoring: A laboratory report[END_REF][START_REF] Howes | Can Laboratories Move Away from Single-Use Plastic?[END_REF] which is a visible part of the goods purchased and thrown away in experimental laboratories. Few debates animate the scientific communities on other purchases, although they can represent a major part of the indirect emissions of an experimental lab. [START_REF] De Paepe | Purchases Dominate the Carbon Footprint of Research Laboratories[END_REF] In this article, we focus on the case of chemical academic research. We quantify the emissions of three French chemistry laboratories that are different in size, location (Figure S1) and fields of expertise. The calculation protocol is based on the opensource web-application GES 1point5 following the GHG protocol. [START_REF] Mariette | An open-source tool to assess the carbon footprint of research[END_REF] This tool was developed by academic staff within the research project Labos 1point5 to meet the specific needs of research laboratories. Research in chemistry has several specificities that could affect its emissions: (i) the consumption of various chemicals, in particular organic solvents used for synthesis, purification and washing; (ii) the intensive use of fume hoods that induces important demands on both electricity and heating; (iii) several devices using extreme conditions by means of temperature (ovens, freezers and cryogenic), high vacuum (electron microscopes, spectrometers), and/or high electrical power (lasers, electromagnets). They add-up to other activities related to the office work, lab life, commutes and travels.

In this work, we estimate the direct and upstream GHG emissions from energy, purchases, travels, and commutes for three laboratories in 2019. For each emission category we further evaluate the objective of a 50 % decrease of GHG emissions by 2030. To do so, we gather and evaluate a pool of reduction measures for chemistry laboratories which are keen to transitioning to low-carbon research. Such a work is a first step in the construction of a rational strategy to tackle, at the lab scale, the humaninduced impacts of research activities on the livability of Earth surface.

Results & Discussion

Purchases and heating dominate emissions. Emissions per capita are displayed on Figure 1 for each of the three laboratories considered. The total emissions span from 4 to 6 teqCO2/pers. with a standard deviation of 1 teqCO2/pers. The variability among laboratories is significant enough to observe a difference between Lab 1 on one side, and Labs 2 and 3 on the other. Looking at emissions broken down by categories, purchases dominate emissions followed by heating for Labs 1 and 3, while the order is inversed for Lab 2. Purchases account for 31-42 % of emissions per capita, while heating represents 23-33 %. A 2-fold variation of heating emissions per capita is observed between Lab 1 and Lab 2, as well as a significant discrepancy in purchaserelated emissions between Lab 1 and Lab 3. The importance of the three other emission categories (electricity, travels and commutes) depends on the laboratory with the electricity share being the most variable (7-18 %), followed by travels (11-16 %) and commutes (8-12 %). We observe that, whatever the chemistry laboratory studied here, the total emissions are equal or higher to the median emissions calculated from the laboratory database of the GES 1point5. [START_REF] De Paepe | Purchases Dominate the Carbon Footprint of Research Laboratories[END_REF] In particular, heating and electricity emissions are 60 to 190 % higher than the GES 1point5 median for the three chemistry laboratories. In the following sections, we detail the analyses of emissions per category, and the associated mitigation strategies.

Purchases

Figure 2A display purchases emissions per capita broken down by sub-category. Lab equipment and consumables dominate purchases emissions for the three laboratories. Additional information is provided in Table S3 concerning the most expensive equipment acquired in Lab 2. Interestingly, the three laboratories have equivalent emissions associated to equipment with an average 0.9 teqCO2, while consumables and other purchases (including hosting, services and lab life) are 2 to 4 times higher for Lab 3, compared to Lab 1 and 2. The remaining maintenance and IT sub-categories account for less than 20 % of purchases emissions. We further analyze consumables emissions by type (Figure 2B) and find that chemicals and lab supplies dominate emissions, followed by solvents and gases, and again, a significant discrepancy exists between laboratories. Especially, emissions associated to chemicals and lab supplies are 3 to 5 times higher in Lab 3 compared to the two others. Purchases category is the most emitting in Labs 1 and 3 (Figure 1) and, therefore, should be targeted by strong reduction actions. It is also the most challenging category as there are many different contributions to purchases, requiring an array of actions. We consider five mitigation strategies (MSs): increase the lifetime of equipment by 25 % (MS1) and further reduce by 25 % lab equipment by pooling (MS2), reduce by 10 % the use of chemicals by pooling (MS3), reduce acetone purchases by recycling (MS4) and increase by 50 % the lifetime of IT equipment (MS5). As MS1 and MS2 imply an increase of maintenance, we apply an increase of their emissions by 50 %. As part of the evaluation of MS4, a life cycle assessment (LCA) is conducted to estimate the effectiveness of recycling acetone in Lab 2, using a distillation/chiller unit (Table S4). The results (Figure 2D) reveal that the emissions resulting from the purchase and use of the distillation/chiller unit are negligible. Consequently, the recycling rate achieved through this unit directly translates into a reduction in emissions associated with the production and disposal of acetone. In addition, a 50% recycling rate yields 35% economic cost savings. These findings highlight the environmental and economic benefits of recycling acetone, especially in laboratories where large quantities are consumed. Implementing a recycling system requires organizational efforts to (i) set a dedicated and safe space for recycling, (ii) adapt the chain of waste disposal and recycled solvent supply, and (iii) use the solvent purposely.

The effectiveness of the mitigation strategies (Figure 2C andS2) is ranked similarly across all laboratories: MS2 ≥ MS1 >> MS5 ~ MS3 >> MS4. Labs 1 and 2 reduce their emissions by approximately 25 %, Lab 3 reduction being 15 %. This disparity is primarily due to the differing distribution of purchases emissions, Lab 3 having a higher proportion of emissions due to consumables. It is worth noting that the increase of maintenance emissions is outweighed by the overall gains achieved through MS1 and MS2. Overall, the five mitigation strategies reduce total GHG emissions by 12 %, 8 % and 6 % in Labs 1, 2 and 3, respectively.

Note that the mitigation strategies do not take consumables reduction into account, although they could be replaced by reusable glassware. Readers interested in this aspect can refer to Howes' paper, [START_REF] Howes | Can Laboratories Move Away from Single-Use Plastic?[END_REF] which discusses single-use plastics in biological laboratories. It is crucial to assess and compare the impacts of potential solutions to ensure that they do not cause burden shifting between life cycle stages. For instance, switching from disposable to reusable lab supplies may reduce the production of raw material and waste generated by the lab, but it may increase the environmental impact associated with cleaning and sterilization of the reusable supplies. Also, the mitigation strategies considered here are demand-driven only, meaning they are based on changes from the users at the lab. The method used to estimate purchase emissions is based on average monetary emission factors, which does not enable to differentiate suppliers. and therefore considering supply-driven strategies. As a result, it is not possible to take into account supply-driven strategies include purchasing more sustainable lab equipment, lab supplies, and chemicals.

Energy

The energy consumption related to electricity and heating categories are comparable in all three labs (details in Figure S3) and ranges from 14 300 kWh/pers. (Lab 3) to 17 000 kWh/pers. (Lab 2). Such amounts are 2 to 3 times higher than the average individual French houses consumption, which is approximately 6 850 kWh/pers/year. [START_REF]Final energy consumption in households per capita[END_REF] The main building of Lab 2 consumes around 10 times more electricity than a similarlysized education building within the hosting university, indicating that electricity consumption is directly connected to research activities. Using fume hoods can also lead to significant heat loss as the air being exhausted is warmer (or cooler) than that being drawn from outside to compensate. Lab 1 consumes more electricity than Labs 2 and 3 by 30 and 80 %, respectively, but it has less heating requirements by 40 %. The discrepancies observed are explained by (i) Lab 1 involves more physics-related activities that require electrically powered equipment, whereas (ii) Labs 2 and 3 have more chemistry-related activities that require the use of fume hoods and subsequent heating compensation.

Energy-associated emissions (Figure 3) range from 1.6 teqCO2/pers (Lab 1) to 2.3 teqCO2eq/pers. (Lab 2). Electricity generates less emissions than heating because France has a low-carbon electricity mix (60 geqCO2/kWh in 2019). In comparison, the world electricity mix generated 475 geqCO2/kWh in 2019. [START_REF]Emissions -Global Energy & CO2 Status Report 2019 -Analysis[END_REF] If the laboratories considered were to use the world electricity mix, the carbon footprint of electricity would be multiplied by 8 and the share of electricity in the total laboratory footprint would go up dramatically, to 65 % for Lab 1 and 33 % for Lab 3. Electricity-related emissions would then dominate all other emission categories for Lab 1 and 2. Concerning heating, fuel sources vary in the three labs: Lab 2 only relies on natural gas (227 geqCO2/kWh), whereas Lab 1 and 3 are furnished through a district heating network based on natural gas and cogeneration (206 and 184 geqCO2/kWh resp.).

Figure 3. GHG emissions associated with energy use per lab in 2019 (top) and mitigation strategies for 2030 (bottom) with: 40 % reduction for electricity and heat; switch to 50 % wood and 50 % geothermal for heating systems (see Table S1 for heating systems in 2019).

Energy management is a crucial factor in decreasing the carbon footprint of chemistry laboratories. French universities are being targeted by the government's plan for energy sufficiency launched in 2022, which aims to achieve a 40 % reduction in energy consumption by 2030. 29 Examples of generic solutions taken at the scale of the University of Bordeaux 30 (host of Lab 2) include daily-life operations and infrastructures, as detailed in Table S5. Alongside general measures, chemistry labs have several levers that are specific to their activity, such as management of fume hoods [START_REF] Mills | Energy use and savings potential for laboratory fume hoods[END_REF][START_REF]My green lab[END_REF][START_REF]The Laboratory Benchmarking Tool[END_REF][START_REF] Posner | A conceptual model for laboratory ventilation greenhouse gas planning[END_REF] , cooling systems (e.g. ultra-low temperature freezers), [START_REF]My green lab[END_REF][START_REF] Gumapas | Factors affecting the performance, energy consumption, and carbon footprint for ultra low temperature freezers: case study at the National Institutes of Health[END_REF][START_REF] Drahl | A Matter of Degree[END_REF][START_REF] Espinel-Ingroff | Long-Term Preservation of Fungal Isolates in Commercially Prepared Cryogenic Microbank Vials[END_REF] , and equipment (e.g. lasers). These examples are further discussed in Table S6. To prioritize efforts, a precise electricity monitoring system is needed. Although it is absent in the studied Labs, data from the Laboratory Benchmarking Tool [START_REF]The Laboratory Benchmarking Tool[END_REF] indicates ventilation uses 35 %, equipment 30 %, cooling 23 %, and lighting 12 % of electricity (from 15 US chemistry and biology labs).

Figure 3 illustrates the potential reduction by implementing energy savings of 40 % and transitioning to renewable energy sources for heating systems. The results indicate a significant decrease in emissions, ranging from 65 % in Lab 3 to 78 % in Lab 2. Notably, the decarbonization of heating systems emerges as the primary lever.

Travels/business trips

The emissions of professional travels are depicted Figure 4 (top graph). They are dominated by long-distance (> 600km) travels by planes, which represent, in the three labs, 87 to 92 % of the emissions. The prevalence is related to cumulated distances of travels by plane being 76 to 82 %, as detailed in Table S7. Besides, trains in France are largely electric with an energy mix mostly nuclear, i.e. poorly carbon emissive (2 to 30 geqCO2/pers./km depending on the type of train) [START_REF] Sncf | Information sur la quantité de gaz à effet de serre émise à l'occasion d'une prestation de transport[END_REF] . Interestingly, in one of the laboratories (Lab 1) the number of trips per person is half as high compared to Lab 2 and 3. In addition, trains are favored in Lab 1 with 21 % of the total distance, compared to Labs 2 (17 %) and 3 (13 %). The smaller travel footprint of Lab 1 could be attributed to its geographic location within the Lille metropolis, a densely populated region that offers convenient train connections to Paris, Belgium, the Netherlands, and the UK. As the predominant impact of professional trips relates to plane travels, it could be reduced either by using less impacting travel means, or by reducing the flight frequency. We assessed the following mitigation strategies on plane travels (Figure 4) which, we believe, combine the quality of international exchange and research dissemination with the follow-up of the Cop21 agreements:

-Travels > 600km: replace 30 % long distance journeys by online conferences, -Travels < 600km: switch from plane to train. The duration of several trips below 600 km are detailed in Table S8.

Combining both measures leads to a ~ 30 % reduction of the travel emissions. To promote train versus plane, French institutions ruled that train should be imposed for trips less than 3 to 4 h. To improve the acceptability of long train journeys, the use of first class would enable staff to work remotely in a comfortable space not afforded in planes. Other incentives may be implemented, such as an extra hotel night to adapt to train schedules, and specific support such as children care for single parents. The train attractiveness (cost, duration, frequency) is also dependent on (i) investing in train network and (ii) tax strategies for plane and trains. For reasons of both social equality and care for the environment, evaluating researchers on the basis of the number of conferences they attend per year (e.g., ERC applications) has become inappropriate.

Commutes

The emissions related to commutes are evaluated via a survey which is detailed in the supplementary information (Figures S5-7 and Table S9). The results show that in Lab 2 and 3, the main means of transportation is the car (mostly thermic), while in Lab 1 it is the subway. The three labs are directly connected to bus, tramways, metro and or trains, so the disparities are not a priori due to infrastructures. The second finding is that young researchers (PhD, post doc) demonstrate a higher inclination towards using the least emissive transportations (public transport, walking, and cycling) than permanent staff. This is possibly due to a shorter commuting distance, lower costs, and perhaps a greater environmental sensitivity. Cars are responsible for 91, 82 and 86 % of the emissions due to commutes, and they emit 0.3, 0.4 and 0.6 teqCO2/pers. for Labs 1, 2 and 3, respectively (Figure 5). This is because cars are the primary mode of commuting, while France's decarbonized electricity leads to low-GHG public transport. In 2019, prior to the COVID-19 pandemic, homeworking was hardly spread in the three laboratories: according to our data, 75 % of Lab 1 employees commuted to work five days a week, while this percentage was 85 % for Labs 2 and 3. Home chemistry is limited to non-experimental tasks. Yet, remote work allows for literature research, writing articles/grants, placing orders, and creating equipment usage protocols. However, telecommuting might lead to rebound effects like longer commutes for those relocating or increased heating expenses for home-based work. [START_REF] Shi | The impact of teleworking on domestic energy use and carbon emissions: An assessment for England[END_REF][START_REF] Simon | Pilot study to measure the energy and carbon impacts of teleworking[END_REF] These effects have not been taken into account because we considered the emissions of staff at home to be outside the scope of the study.

We center commutes mitigation measures on replacing cars with strategies that depend on the home-to-work one-way distance (Figure 5):

-0 ≤ 5 km: trips made by thermic car are substituted by bicycle or walk -5 ≤ 10 km: trips made by thermic car are substituted by electric bike (50 %) or subway/train (50 %) -+ 10km: trips made by thermic car are substituted by electric car (33 %) or by carpooling with 2 persons/car (33 %). In addition to this, 33 % of people work from home 1 day per week.

Travels made by any means of transportation except thermic cars are kept unchanged.

Summary of the actions

Figure 6 summarizes emissions in 2019 and projected for 2030 if all the mitigation strategies discussed above were to be implemented. The result is encouraging, with a total reduction in emissions in the range 40-50% for the three laboratories. If we consider absolute reductions by source, heating represents 40-50% of the reduction effort, followed by purchases (15-25%) and electricity, then travels and commutes (5-10% each). In this scenario, half of the reduction efforts depend on the institution (heating) while the other half is directly controlled by the laboratory. When we look at the relative reduction by category, heating emissions are divided by 15, commutes by 2, and the other three categories go down by 15-30 % of the initial value.

Conclusion & outlook

Our calculations of the 2019 carbon footprint for the three laboratories yield an average carbon footprint per researcher of ca 5.6 teqCO2. This ranks chemistry laboratories slightly higher than the median of 5.0 teqCO2, calculated on the basis of 100 laboratories from all disciplines using the same methodology. [START_REF] De Paepe | Purchases Dominate the Carbon Footprint of Research Laboratories[END_REF] It is important, for such comparisons, to pay attention to any possible variation in scope. A recent study from Martin et al. showed a yearly 28 teqCO2/pers. emission for an astronomical institute. [START_REF] Martin | A comprehensive assessment of the carbon footprint of an astronomical institute[END_REF] However, Martin et al's work includes specific large research infrastructures. Specific large facilities such as characterization platforms and synchrotron are also used in chemistry, but were not taken into account in this study. Larsen et al. obtained 14 teqCO2/pers. for the Natural Sciences department of a Norwegian technical university, including building construction and central administration. If these two categories were not considered, the GHG emission would be 7 teqCO2/pers. which is close to our results. [START_REF] Larsen | Investigating the Carbon Footprint of a University -The case of NTNU[END_REF] One limitation of our study is the use of monetary emission factors for assessing the GHG emissions of purchases. LCA based on physical flows are in principle more precise, but on the one hand laboratory accountability is monetary, not mass accounting, and LCA does not give accurate results for niche products where production costs are small relative to research & development ones. [START_REF] De Paepe | Purchases Dominate the Carbon Footprint of Research Laboratories[END_REF][START_REF] Font | The role of services and capital in footprint modelling[END_REF] As a result, a cooperative effort between researchers and suppliers is needed to refine emission factors of laboratory supplies and equipment. Other categories have their own bias. For instance, one could argue that staff responding to the commuting questionnaire is the most concerned one. It is also important to recognize that assessing the carbon footprint alone provides an incomplete understanding of the overall environmental impact of the laboratories. Other environmental factors, such as the emission of toxic, acidifying and eutrophying substances, water use and resource depletion, have to be considered. For example, the adoption of electric cars is associated with higher mineral resource usage compared to thermic cars, and the utilization of wood for heating can generate fine particulate matter. Thus, it is recommended to conduct LCAs to assess specific mitigation strategies and avoid burden shifting. On a broader perspective, the use of LCA can help chemists to identify the most impactful stages and materials in their research and product development. [START_REF] Kralisch | Rules and benefits of Life Cycle Assessment in green chemical process and synthesis design: a tutorial review[END_REF][START_REF] Raccary | Life cycle assessment of sample preparation in analytical chemistry: a case study on SBSE and SPE techniques[END_REF] Altogether, our mitigation strategies show a possible reduction of 40 to 50 % for the three laboratories, which is very encouraging. However, this implies a combination of actions at the level of the government (e.g. public transportation), the university (e.g. thermal isolation of buildings) and the individual (e.g. proper use of the sashes). Collective actions are generally difficult to implement, unless strong incentives are given by the administration. Similarly, individual actions (such as reducing flying for professional purpose) are easier to accept when one feels that others share the burden. In addition, the organization of the academic system itself has a strong impact over the environmental burden of research. Indeed, a number of works identified how professional success is associated to international travels. [START_REF] Berné | The carbon footprint of scientific visibility[END_REF][START_REF] Wynes | Academic air travel has a limited influence on professional success[END_REF] International collaborations, invitations to international conferences or as invited professor are considered as markers of scientific excellence. Moreover, the current funding model, which prioritizes project-based investments, tends to favor purchasing new equipment, whereas a more sustainable approach could be achieved by allocating resources to hiring additional staff for equipment maintenance and the design of customized solutions. Beyond research policy, the whole society has evolved towards an intensive use of technology. As in other sectors, the access to innovative technologies has pushed the academics to carry out more numerous and more sophisticated experiments, possibly to the detriment of the intellectual input. Rationalizing the experimental part of research [START_REF] Mincigrucci | The carbon footprint of research papers[END_REF] (by identifying useless experiments and oversized analysis) should lead to a significant decrease of the environmental impact of research. Additionally, substantial financial savings could be redirected to recruit people to achieve administrative tasks or take environmental actions. Some researchers may also decide to spend more time teaching, rethink the purpose of their research, or organize transitions. In particular, more efforts could be devoted to green chemistry and energy savings.

Overall, conducting research from a sustainable development perspective requires a multidisciplinary approach. Social sciences are particularly important, since they can help to anticipate the behavior of societies with respect to current environmental challenges and to accompany the change toward a more sustainable research.

Methods

We investigate three laboratories located in three French metropoles: Lille, Bordeaux and Rennes (Table S1 and Figure S1). The laboratories cover a wide range of chemistry disciplines with some differences between laboratories: Lab 1 focuses on physical and analytical chemistry while Labs 2 and 3 also include organic and inorganic synthesis, as well as theoretical chemistry. We quantify the carbon footprint of each laboratory for the year 2019 using GES 1point5, [START_REF]Labos 1point5. GES 1point5[END_REF] a web application specific to the research sector. [START_REF] Mariette | An open-source tool to assess the carbon footprint of research[END_REF][START_REF] De Paepe | Purchases Dominate the Carbon Footprint of Research Laboratories[END_REF] The data are distributed in four categories: (i) buildings (related to electricity and heating consumption of buildings), (ii) purchase of goods and services (including IT), (iii) business travels and (iv) commutes. Electricity and heating emissions are calculated from annual consumption figures from the buildings associated to each laboratory. When a single building is shared with other services, the corresponding part of energy consumption is attributed by the surface share. In 2019, the French electricity mix was composed of 70.6 % nuclear, 11.2 % hydraulics, 7.9 % fossil combustibles (gas, coal, petrol), 6.3 % wind, 2.2 % solar, 1.8 % bioenergies, [START_REF]Bilan électrique[END_REF] corresponding to 60 geqCO2/kWh. Professional travel emissions are calculated by compiling, for each travel, the geodesic distance and the type of vehicle with the corresponding kilometric emission factor (EF). Emissions associated to flying include the effect of contrails. Commute emissions are determined via a questionnaire (managed by GES 1point5, see §Commutes in SI for details) [START_REF] Mariette | An open-source tool to assess the carbon footprint of research[END_REF] submitted to the following staff members: PhD students, postdocs, administrative and technical staff, assistant professors, professors and permanent researchers. They can choose up to two types of commuting distances and means of transport representative of a typical working week. The rate of answers was approximately 50 % and the total commute emissions were proportionally extended for each socio-professional class. Purchases emissions are estimated by combining two procedures. For the small fraction of purchases related to office computers, emissions are evaluated per unit using suppliers EFs. For all other purchases, excluding travel tickets, emissions are calculated by multiplying their tax free price by the monetary emission factors of the GES 1point5 EF database [START_REF] De Paepe | Purchases Dominate the Carbon Footprint of Research Laboratories[END_REF] (Table S2). This hybrid EF database combines environmentally extended input-output (EEIO) EFs with corrections that either use LCA or supplier prices to estimate monetary EFs for gases, plastic-ware and gloves or carbon intensities from representative companies that sell certain types of goods to research labs (such as Sigma-Aldrich for chemical products, for instance). All purchase-associated EFs are cradle-to-gate, i.e. from including production and transport to the point-of-sale. The different goods and services are identified through the NACRES accountability identification system used in French academic institutions. Annual emissions per capita are computed by dividing annual emissions by the number of staff, considering all persons working in the laboratory for the full year 2019 (including technicians and lab administrative support staff). Uncertainties are calculated according to the GES 1point5 tool. [START_REF] Mariette | An open-source tool to assess the carbon footprint of research[END_REF][START_REF] De Paepe | Purchases Dominate the Carbon Footprint of Research Laboratories[END_REF] The following emissions are not considered: emissions related to (i) building construction, (ii) the use of large research infrastructures (such as large servers, synchrotron etc.), (iii) instrumentation owned by the laboratory before 2019, (iv) staff meals. References to the full results can be found on the GES 1point5 website: Lab 1: LASIRE; 48 Lab 2: ISM; [START_REF]GES 1point5 & ISM[END_REF] Lab 3: ISCR. [START_REF]GES 1point5 & ISCR. BGES[END_REF] Starting from the carbon footprint of the three laboratories in 2019, we identify GHG mitigation strategies, for the most significant items, with the aim of reducing emissions by 50 % in 2030, compared to 2019 levels. This objective is aligned with the "Plan Climat du MESR" published in November 2022 by the French Ministry of Higher Education, Research, and Innovation. 29 Firstly, we review existing sustainability plans or policies at the hosting university or research center. These plans often include specific actions that could be implemented to reduce GHG emissions, such as the use of renewable energy categories. We prioritized these actions as they are already planned and endorsed by the hosting institution. Secondly, we conducted a review of existing literature on GHG reduction solutions for research laboratories, including peerreviewed articles, government reports, and sustainability guides specific to chemistry. [START_REF] Durgan | Green Labs: a guide to developing sustainable science in your organization[END_REF][START_REF]Sustainable laboratories -practices to reduce the environmental effects of research[END_REF] Finally, we engaged in discussions with colleagues in the laboratories and across the hosting institutions to gather their valuable perspectives and insights on GHG reduction solutions.

Acetone is one of the main solvents used in laboratories. For instance, Lab 2 and Lab 3 consume annually 3 700 and 10 000 liters of acetone, respectively. Their incineration induces the emission of 6.6 and 18.1 teqCO 2, respectively. Table S4. Life cycle assessment conducted to compare the carbon footprint and cost related to three scenarios of acetone supply in Lab 2.

The life cycle assessment (LCA) is conducted in order to compare the carbon footprint and costs of three acetone recycling scenarios in Lab 2. The functional unit of this comparative LCA is "to provide 3 710 L of acetone to Lab 2", which is equivalent to the yearly demand of this solvent. The assessed scenarios are: 1) business-as-usual 0% recycling, 2) 10% recycling, and 3) 50% recycling. The boundaries are "cradle-to-grave" and include the production and transport of acetone, distillation of the solvent (manufacture and use of the distillation/chiller unit), evaporation of acetone during distillation, transport and incineration of the waste solvent. Emission factors for the different elements have been calculated with ecoinvent 3.9 life cycle inventory database + IPCC life cycle impact assessment method, and directly from GES1point5 for electricity. Inventory associated to the manufacture of the distillation/chiller unit has been built through an estimation of the metal/plastics/electronic content of the machines.

Fume hoods management

The work from Posner et al. indicate that a clever use of the fume hoods could reduce the electrical consumption of the extraction system by 30 % (direct reduction by less air pumping and indirect reduction by air compensation, possibly heated or cooled in winter/summer), 2 which is in line with previous estimations. 3 Since 2023, the recommendations given to all chemists in Labs 2 and 3 are the following: (i) fume hoods must have their sash down in the absence of operator, which is also a safety requirement, and (ii) fume hoods must be turned off when all containers stored underneath are closed.

Ultra-low temperature freezers

Regular cleaning/defrost of the freezers and their maintenance and location in a room at less than 25° C allow to decrease their energy consumption down to 25 % and increases their life time. 4 In addition, following the recommendations of MyGreenLab 5 , shifting ultra-low freezer from -80° C to -70° C reduces the energy consumption of those machines by 30-40 %, without damaging the cell lines. 6 , 7

Lasers

Replacing gas lasers with diode lasers in spectroscopy devices, such as Raman and infrared spectrometers, is a significant step towards achieving energy savings for equipment. Diode lasers offer higher electrical-to-optical conversion efficiency, resulting in reduced energy consumption and lower operating costs. In Lab 2, two gas lasers with power outputs of 15 kW and 21 kW, along with a water consumption rate of 10 L/min, were recently replaced by two diode lasers with power outputs of 30 W and 63 W, eliminating the need for water consumption entirely. This transition allows for a remarkable 99 % reduction in both energy and water usage for these specific applications. However, further LCA studies must be conducted to ensure the avoidance of any potential burden shifting during manufacturing of diode lasers. One main issue is that diode lasers lifetime might be reduced compared to gas lasers.

Commuting

In order to know the mode of transportation of the employees of the different laboratories, an online survey (managed via the GAS 1point5 tool) [START_REF] Klöwer | An analysis of ways to decarbonize conference travel after COVID-19[END_REF] was sent to all the staff (PhD, post-doc, techs., researchers/teachers). The questions were the following: 1. In 2019, on average, when you were not on vacation, how many days per week did you go to your workplace?

Figure 1 .

 1 Figure 1. GHG emissions per capita for the three laboratories per emission category. Gray: "Lab 1p5" represents the median laboratory emissions from the GES 1point5 database (>100 laboratories from all disciplines).

Figure 2 .

 2 Figure 2. Purchases emissions and mitigation strategies. A: Purchases emission from the three laboratories for year 2019 ("others" comprises hosting, services and lab life). B: Focus on consumables ("others" comprises biochemistry and biology supplies). C: Projected emissions in 2030 by implementation of the mitigation strategies discussed in the text. D: Comparison of yearly GHG emissions and cost associated with different acetone recycling scenarios for Lab 2. "Machines" comprise the cost and GHG emissions associated to the production and electricity consumption of the distillation/chiller system; "Waste" comprises the cost of solvents destruction by an external companyand GHG associated to their incineration and transport to the incinerator; "Acetone" comprises the cost and GHG emissions of purchases and associated production. It also takes into account the losses by evaporation of acetone that is degraded in CO2.

Figure 4 .

 4 Figure 4. GHG Emissions associated with professional travels per lab in 2019 (top) and mitigation strategies for 2030 (bottom) with: short distance plane trips (< 600 km) replaced by train trips and 30 % long distance trips replaced by remote attendance.

Figure 5 .

 5 Figure 5. GHG Emissions associated with commutes per lab in 2019 (top) and mitigation strategies for 2030 (bottom) with 0-5 km: trips made by thermic car are made by bicycle or walking; 5-10 km: trips made by thermic car are made by electric bike or subway/train; +10km: trips made by thermic car are made either by electric car or by carpooling (2 person/car) + people work from home 1 day per week on average. Distances are one-way home-to-work.

Figure 6 .

 6 Figure 6. Scenarios of emissions for the three labs. GHG emissions by category in 2019, and projected in 2030 if the mitigation strategies discussed in this work are implemented.

Figure S4 .

 S4 Figure S4. Modes of transportation used during business trips (conferences, seminars, PhD committees...) for the three labs (top) and associated GES (down). Data are normalized per persons. Amplitudes are represented on a logarithmic scale.

Table S6 .

 S6 Measures for the reduction of electricity-related GHG emissions that are specific to chemistry activities.

			S c enario	S c enario
		S c enario	rec yc ling	rec yc ling
	Inv entory data	rec yc ling 0	0.1	0.5
	Y early purc has e of ac etone (L )	3 710	3 346	1 892
	Y early purc has e of ac etone (kg )	2 909	2 618	1 454
	A c etone rec yc ling rate	0%	10%	50%
	Y early amount of rec yc led ac etone (L )	-	371	1 855
	E lec tric ity c ons umption dis tiller/c hiller (kW h)	285	1 425
	G HG emis s ions (kg C O2eq/year)	12 416	11 202	6 349
	A c etone produc tion	5 535	4 993	2 823
	W as te trans port	336	302	168
	W as te inc ineration	6 544	5 890	3 272
	E lec tric ity dis tiller/c hiller	-	17	85
	Manufac turing dis tiller/c hiller		123	123
	A c etone evaporation and deg radation	-	17	84
	C os t (€/year)	6 245	6 407	4 121
	A c etone purc has e	5 194	4 685	2 649
	W as te treatment	1 051	946	526
	E lec tric ity dis tiller/c hiller	-	43	214
	P urc has es dis tiller/c hiller		733	733
	Unitary c os t and emis s ion fac tors	€	kg C O2eq per	S ourc e
	E lectricity (F R )	0.15	0.0599 kW h	AD E ME
	A c etone produc tion	1.4	1.492 L	ec oinvent 3.9 + IP C C
	A c etone inc ineration	0.36	2.25 kg	s toec hiometric c ombus tion
	L orry trans port		0.21 tkm	ec oinvent 3.9 + IP C C
	D is tiller manufac turing	7000	1589 unit	ec oinvent 3.9 + IP C C
	C hiller manufac turing	3500	260 unit	ec oinvent 3.9 + IP C C
	Other data
	E vaporation rate of ac etone during dis til.	2%
	A c etone dens ity	0.784 kg /L
	W as te treatment plant dis tanc e (B dx/L yon)	550 km
	P ower of the c hiller	0.52 kW
	P ower of the dis tiller	2.04 kW
	C adenc e dis tiller per run	4.5 h
	V olume dis tiller per run (up to 30L )	15 L
	L ife time of the dis tiller	15 yr
	L ife time of the c hiller	15 yr

Table S9 .

 S9 2. What modes of transportation did you use on the most frequent typical day in 2019? (Possibility to enter a 2nd typical day later if you have very different trips in the same week). (Choose between: walk, bike, electric bike, electric scooter, moto, car, city bus, long-distance bus, tramway, train, metro). 3. What were the total distances you traveled to and from on the most typical day in 2019? 4. Do you have another frequent typical day to report in 2019? (yes→go back to question 2 / no→question 5) 5. Simulation answer Answers of the commuting survey. Category are: Researchers/teachers (α), technical staff/engineers (β), PhD and Post-doctoral fellows (γ)

		Lab 1			Lab 2			Lab 3
	Category	α	β	γ	α	β	γ	α	β	γ
	total	27	17	32	78	51	93	204 80	180
	answers	24	10	8	46	35	26	113 61	46
	% answers	90% 57% 25% 59% 69% 28% 55% 76% 26%

[START_REF] Klöwer | An analysis of ways to decarbonize conference travel after COVID-19[END_REF]

Mariette, J.; Blanchard, O.; Berné, O.; Aumont, O.; Carrey, J.; Ligozat, A.; Lellouch, E.; Roche, P.-E.; Guennebaud, G.; Thanwerdas, J.; Bardou, P.; Salin, G.; Maigne, E.; Servan, S.; Ben-Ari, T. An Open-Source Tool to Assess the Carbon Footprint of Research. Environ. Res.: Infrastruct. Sustain. 2022, 2 (3), 035008. https://doi.org/10.1088/2634-4505/ac84a4. Figure S7. Lab 3 commute survey results (year 2019). Answers rate: 47 %.

Univ Bordeaux. Le plan de sobriété énergétique de l'université de Bordeaux. https://www.ubordeaux.fr/actualites/plan-sobriete-energetique (2022).

Funding

This work was conducted as part of the research network GDR Labos 1point5, funded by ADEME, CNRS and INRAE. It was further funded by Bordeaux INP and Université de Rennes.

Graphical abstract

SUPPLEMENTARY INFORMATION The electronic supplementary information is available free of charge at http://XXXX. It includes details on the context of the study (Table S1, Figure S1), details on purchase/equipment, including LCA case study on acetone distillation (Tables S2-S4), additional figures for purchases (Figure S2), energy (Figure S3, Tables S5,S6), travels/business trips (Table S7, S8, Figure S4), commutes (Table S9, Figures S5-S7).

Author Contributions

All the authors contributed equally to the manuscript and gave approval to its the final version.

Electronic Supporting Information

Carbon footprint and mitigation strategies of three chemistry laboratories

Energy

Figure S3. Energy consumptions for year 2019 of the three labs (top) and associated emissions (down).

Note that in France the electricity is mainly produced by nuclear fission.

Table S5. Measures for the reduction of heat-related GHG emissions, from reduction plan of the University of Bordeaux

Daily-life operations

n removal of hot water for sanitary purposes (except showers), n removal of auxiliary electric heaters in favor of a collective regulation, n optimization of outdoor lightning (e.g., turning off parking lot lightning from 1.00 to 5.00 AM), n reduction of heating at night, on weekends and for summer and winter breaks, n schedules of heating times accorded to room booking tools, temperature at 19° C in winter when the buildings are occupied and 16° C when not, n end of comfort air-conditioning, n minimum 26 °C air-conditioning when necessary.

Infrastructures

n switch from natural gas to biomass and geothermy for heating systems, n installation of photovoltaic panels, n insulation of buildings.

Travels/business trips