Pesticide usage has been expanding since the 1950s. Their use has been known to harm human and environmental health for decades. Pesticide volatilisation to the atmosphere is a known process which is however not well documented, especially for periods beyond a few days after pesticide application. This is partly due to the difficulty to measure gaseous pesticides concentration in the atmosphere continuously for long time periods. Indeed, current state-of-the-art measurements is made by thermo-desorption gaseous chromatography involving semi-manual sampling with cartridges.In this study, we report first monthly outdoor online measurement of concentrations and volatilisation of one fungicide and two herbicides by proton transfer reaction, quadrupole injection, time of flight, mass spectrometry (PTR-QI-TOF-MS). The fungicide Chlorothalonil was measured over a wheat field in spring, while the herbicides Prosulfocarb and Pendimethalin were measured over a bare soil in autumn. Comparison with state-of-the-art TD-GC-MS and calibration by a home-made permeation system proved the PTRMS to be adapted for pesticides measurements.Maximum measured concentrations ranged from 12 ppt for Chlorothalonil to 600 ppt Prosulfocarfb. Maximum daily volatilisation fluxes ranged from 35 ng m-2 s-1 for Chlorothalonil to 350 ng m-2 s-1 for Prosulfocarb. We found that volatilisation of Chlorothalonil lasted more than three weeks, leading to up to 50% of the applied quantity volatilised, a duration and an amount much larger that what has been reported before.Volatilisation of pesticides may contribute much more significantly than expected to atmospheric burden, and be wet and dry deposited over larger areas. Further PTRMS pesticides measurements should be done to gain insight into pesticide transfer to the environment, and better characterize human exposure to these harmful compounds.

Abstract. Biogenic volatile organic compounds (BVOCs) play a large role in atmospheric chemistry as they are precursors of ozone and secondary organic aerosols. However, the analysis of their emission in croplands is scarce. This work constitutes, to our knowledge, the first quantification of ecosystem-scale biogenic volatile organic compounds (BVOC) fluxes exchanged over a rapeseed crop field. The experimental campaign took place at the FR-Gri ICOS site (near Paris, France) between spring and summer 2017, during which the BVOC fluxes were measured continuously by the eddy-covariance method with a proton-transfer quad-injection time-of-flight mass-spectrometer instrument (PTR-Qi-TOF-MS). Standard emission factors (SEF) and OH reactivity fluxes were computed from the measured fluxes, and compared to the widely used model MEGAN2.1. Fifty-three BVOCs were significantly emitted or deposited during the campaign. Methanol was by far the most emitted one (83 to 91 % of summed emissions), followed by ethanol (1.5 to 11 %) and monoterpenes (1.2 to 1.6 %). Methanol SEF appeared to be overestimated during vegetation stages in MEGAN2.1. In addition, a 4-fold increase of emissions during the late senescence stage confirmed the necessity to use the ageing factor to represent methanol emissions in MEGAN2.1. Most noticeably, monoterpenes SEF computed in this study were 3 to 90 times larger than with MEGAN2.1. Consequently, this study shows that the share of OH reactivity represented by terpenoid compounds was underestimated in previous studies, pointing out the potentially more significant contribution of croplands to secondary organic aerosol formation.

Pesticide usage has been expanding since the 1950s. However, their use has been known to harm human and environmental health for decades. Recent studies have shown that these two factors are impacted by pesticide diffusion in the atmosphere. The gaseous diffusion of pesticides in the atmosphere is known as volatilization. Although it is a known process, pesticide volatilization has been scarcely measured, especially for periods beyond a few days after pesticide application. Pesticide concentration is usually measured mainly by offline gas-chromatography mass spectrometry, which makes it difficult to deploy in the field for long-term studies. In this study, we report the first online concentration measurements of Chlorothalonil, a fungicide, over a wheat field using a highly sensitive proton transfer reaction, quadrupole injection, time of flight, mass spectrometer (PTR-QI-TOF-MS) for several weeks after its application. The volatilization computed by inverse dispersion modeling was sustained over more than three weeks, leading to up to 50% of the applied quantity being lost by volatilization. High-temporal volatilization dynamics indicate that the understorey contributes significantly to the emissions. Our findings suggest that Chlorothalonil volatilization may contribute significantly to atmospheric exposure, and transfer by deposition to nearby fields and over larger areas. Online PTR-QI-TOF-MS measurements should be developed further to quantify human exposure and the spread of pesticides through the atmosphere.

New Particle Formation (NPF) is a major source of ultrafine particles that affect both air quality and climate. Despite emissions from agricultural activities having a strong potential to lead to NPF, little is known about NPF within agricultural environments. The aim of the present study was to investigate the occurrence of NPF events at an agricultural site, and any potential relationship between agricultural emissions and NPF events. A field campaign was conducted for 3 months at the FR-Gri-ICOS site (France), at an experimental farm 25 km west of Paris city centre. 16 NPF events have been identified from the analysis of particle number size distributions; 8 during the daytime, and 8 during the night-time. High solar radiation and ozone mixing ratios were observed during the days NPF occurred, suggesting photochemistry plays a key role in daytime NPF. These events were also associated with higher levels of VOCs such as isoprene, methanol, or toluene compared to non-event days. However, ammonia levels were lower during daytime NPF events, contributing to the hypothesis that daytime NPF events were not related to agricultural activities. On the other hand, temperature and ozone were lower during the nights when NPF events were observed, whereas relative humidity was higher. During these nights, higher concentrations of NO2 and ammonia were observed. As a result, agricultural activities, in particular the spreading of fertiliser on surrounding crops, are suspected to contribute to night-time NPF events. Finally, all the identified NPF events were also observed at SIRTA monitoring station 20 km from the FR-Gri ICOS site, showing that both night-time and daytime NPF events were regional processes. We hypothesise that night-time NPF may be related to fertiliser spreading over a regional scale, as opposed to the local activities at the farm. To our knowledge, this is the first time night-time NPF has been observed in the agricultural context.

New Particle Formation (NPF) is a major source of ultrafine particles that affect both air quality and climate. However, little is known about NPF in agricultural environments, despite a strong potential considering the nature of emissions from agricultural activities. The aim of the present study was to investigate the occurrence NPF events at a an agricultural site and the potential relation between agricultural emissions and NPF events. A field campaign has been conducted for 3 months at the FR-Gri ICOS site (France) within an experimental farm 25 km west from Paris city centre.16 NPF events have been identified by analysing the particle number and size distribution, 8 during daytime, and 8 during nighttime. High solar radiation and ozone mixing ratios were observed the days NPF occurred, suggesting a key role of photochemistry in daytime NPF. These events were also associated to higher levels of VOCs such as isoprene, methanol, or toluene. However, ammonia levels were lower during daytime NPF events, leading to the conclusion that daytime NPF events were not related to agricultural activities.On the opposite, temperature and ozone were lower the nights when nighttime NPF was observed, whereas relative humidity was higher. During these nights, higher concentrations of NO2 and ammonia were observed. As a result, night-time NPF events were suspected to be related to agricultural activities, and in particular the spreading of fertilizer on surrounding crops.Finally, all the identified NPF events were also observed at a monitoring station 20 km from the FR-Gri ICOS site, showing that both nighttime and daytime NPF events were regional processes. We hypothesize that nighttime NPF may be related fertilizer spreading over a regional scale, rather to the local activities at the farm. To our knowledge, this is it the first time nighttime NPF is observed in the agricultural context.

Volatile organic compounds (VOCs) contribute to air pollution through the formation of secondary aerosols and ozone and extend the lifetime of methane in the atmosphere. Tropospheric VOCs originate to 90 % from biogenic sources on a global scale, mainly from forests. Crops are also a potentially large yet poorly characterized source of VOCs (30 % of the VOC emissions in Europe, mostly oxygenated). In this study, we investigated VOC fluxes over a winter wheat field by eddy covariance using a PTR-Qi-TOF-MS with high sensitivity and mass resolution. The study took place near Paris over a 5-week period and included flowering, crop maturity and senescence. We found a total of 123 VOCs with fluxes 3 times above the detection limit. Methanol was the most emitted compound with an average flux of 63 µg m−2 h−1, representing about 52 % of summed VOC emissions on a molar basis (36 % on a mass basis). We also identified ethanol, acetone, acetaldehyde and dimethyl sulfide among the six most emitted compounds. The third most emitted VOC corresponded to the ion m/z 93.033. It was tentatively identified as furan (C6H4O), a compound not previously reported to be strongly emitted by crops. The average summed VOC emissions were about 173 ± 6 µg m2 h−1, while the average VOC depositions were about 109 ± 2 µg m−2 h−1 and hence 63 % of the VOC emissions on a mass basis. The net ecosystem flux of VOCs was an emission of 64 ± 6 µg m−2 h−1 (0.5 ± 0.05 nmol m−2 s−1). The most deposited VOCs were identified as hydroxyacetone, acetic acid and fragments of oxidized VOCs. Overall, our results reveal that wheat fields represent a non-negligible source and sink of VOCs to be considered in regional VOC budgets and underline the usefulness and limitations of eddy covariance measurements with a PTR-Qi-TOF-MS.

Exchanges of biogenic volatile organic compounds (BVOC) between plants and the atmosphere are likely to vary, in amount and composition, between different plant species but also for a single plant during its development. However, the effect of plant development stages, including senescence, on BVOC exchanges remains poorly investigated, especially in the case of crop plants. We investigated the BVOC exchange patterns for wheat plants, the most grown crop species worldwide, during seed maturation, senescence and after harvest. Fluxes were measured online, in situ, at the plant scale by combining automated chambers and a Proton Transfer - Reaction - Quadrupole ion guide - Time of Flight - Mass Spectrometer (PTR-Qi-Tof-MS). The high resolution and sensitivity of this method enabled the measurement of a large mass spectrum of compounds emitted at very small amounts, allowing a precise characterization of BVOC exchanges. We found that the overall BVOC emissions increased twofold during the senescence stage compared to the maturation stage. Methanol was found to be the most emitted compound (49–60% of the overall flux on a molar basis) followed by acetone (7.5–8.2% of the overall flux on a molar basis) during each developmental stage investigated. Acetaldehyde was another major emitted compound contributing mainly during late senescence to the overall flux (9.7%). When normalized for temperature and light conditions, most BVOC emissions increased during senescence, showing a clear effect of senescence on BVOC exchanges. Chamber emissions were comparable to whole ecosystem fluxes measured at the same site by eddy covariance the previous year. The OH reactivity of the emitted compounds was evaluated based on known reaction rate constants and was the largest during the first senescence stage, peaking at 12 s−1 in the chambers. The results of this study show the need for considering plant phenology when computing BVOC emissions from crops.

Croplands remain poorly studied ecosystems in terms of total hydroxyl radical (OH) reactivity, especially when compared to forests. As part of the COV3ER project, total OH reactivity (ROH), defined as the total loss rate of OH due to its reaction with reactive species in the atmosphere, was characterized in a rapeseed field (Grignon, France) during the blooming season in April 2017. Measurements were performed in a dynamic chamber as well as in ambient air using the Comparative Reactivity Method (CRM). Complementary measurements of organic (including a proton transfer reaction quadrupole ion–time of flight mass spectrometry, PTRQi-ToFMS) and inorganic compounds were also performed in order to calculate the expected OH reactivity and evaluate the missing fraction. Measured ROH varied diurnally in the dynamic chamber (mROHchamber) with maxima around 20 to 30 s−1 at midday and minima during dark hours, following the variability of the enclosed branch VOCsrapeseed, which is light- and temperature-dependent. Oxygenated VOCs were the major compounds emitted by the rapeseed crop. However, in terms of contribution to OH reactivity, isoprene accounted for 40% during the daytime, followed by acetaldehyde (21%) and monoterpenes (18%). The comparison between mROHchamber and calculated ROH (cROHchamber) exhibited little or no difference during dark hours, whereas a maximum difference appeared around midday, highlighting a significant missing fraction (46% on average during daytime) mainly related to biogenic temperature- and/or light-dependent emissions.

Trace gas measurements were performed during the LANDEX (the LANDes EXperiment) Episode 1 field campaign in the summer 2017, in one of the largest European maritime pine forests (> 95% Pinus pinaster) located in southwestern France. Efforts have been focused on obtaining a good speciation of 20 major biogenic volatile organic compounds (BVOCs, including pinenes, carenes, terpinenes, linalool, camphene, etc.). This was made possible by the development of a new and specific chromatographic method. In order to assess the role of BVOCs in the local gas phase chemistry budget, their reactivity with the main atmospheric oxidants (hydroxyl radicals (OH), ozone (O3) and nitrate radicals (NO3)) and the corresponding consumption rates were determined. When considering the OH reactivity with BVOCs, isoprene and linalool accounted for 10–47% of the OH depletion during daytime, and monoterpenes for 50–65%, whereas monoterpenes were the main contributors during the night (70–85%). Sesquiterpenes and monoterpenes were the main contributors to the ozone reactivity, especially β-caryophyllene (30–70%), with a maximum contribution during nighttime. Nighttime nitrate reactivity was predominantly due to monoterpenes (i.e. 90–95%). Five specific groups have been proposed to classify the 19 BVOCs measured in the forest, according to their reactivity with atmospheric oxidants and their concentrations. The total amount of BVOCs consumed under and above the forest canopy was evaluated for 7 BVOCs (i.e. isoprene, α-pinene, β-pinene, myrcene, limonene + cis-ocimene and Δ3-carene). The reactivity of atmospheric oxidants and BVOCs at a local level are discussed in order to highlight the compounds (BVOCs, other VOCs), the atmospheric oxidants and the main associated reactive processes observed under the canopy of a maritime pine forest.

Total hydroxyl radical (OH) reactivity measurements were conducted during the LANDEX intensive field campaign in a coniferous temperate forest located in the Landes area, southwestern France, during July 2017. In order to investigate inter-canopy and intra-canopy variability, measurements were performed inside (6 m) and above the canopy level (12 m), as well as at two different locations within the canopy, using a comparative reactivity method (CRM) and a laser photolysis–laser-induced fluorescence (LP-LIF) instrument. The two techniques were intercompared at the end of the campaign by performing measurements at the same location. Volatile organic compounds were also monitored at both levels with a proton transfer time-of-flight mass spectrometer and online gas chromatography instruments to evaluate their contribution to total OH reactivity, with monoterpenes being the main reactive species emitted in this forest dominated by Pinus pinaster Aiton. Total OH reactivity varied diurnally, following the trend of biogenic volatile organic compounds (BVOCs), the emissions and concentrations of which were dependent on meteorological parameters. Average OH reactivity was around 19.2 and 16.5 s−1 inside and above the canopy, respectively. The highest levels of total OH reactivity were observed during nights with a low turbulence (u*≤0.2 m s−1), leading to lower mixing of emitted species within the canopy and thus an important vertical stratification characterized by a strong concentration gradient. Comparing the measured and the calculated OH reactivity highlighted an average missing OH reactivity of 22 % and 33 % inside and above the canopy, respectively. A day–night variability was observed on missing OH reactivity at both heights. Investigations showed that during daytime, missing OH sinks could be due to primary emissions and secondary products linked to a temperature-enhanced photochemistry. Regarding nighttime missing OH reactivity, higher levels were seen for the stable and warm night of 4–5 July, showing that these conditions could have been favorable for the accumulation of long-lived species (primary and secondary species) during the transport of the air mass from nearby forests.

Monoterpenes (MTs) represent an important family of biogenic volatile organic compounds (BVOCs) in terms of amount and chemical diversity. This family has been extensively studied using gas chromatography (GC) and proton transfer reaction-mass spectrometry (PTR-MS). Upon recent advances with Fast Gas Chromatography (FastGC), it was also commercialized with proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) instruments. The combination of both techniques showed promising results in the near real-time separation of isomers, with the need of further improvements. In this study, a FastGC prototype was coupled to a conventional PTR-MS (PTR-QuadMS). Extensive laboratory experiments were performed, in order to test the system’s performance and to optimize its operational parameters for MT separation. The detection limit was determined to be around 0.8–1.7 ppbv, depending on the MT. The system was afterwards deployed during a three-week field campaign in a mixed holm oak (Quercus ilex) forest known for its important MT emissions. MTs were measured in the incoming and the outgoing air of dynamic enclosures installed on the branches of four different trees. Three chemotypes of holm oak trees could be distinguished showing consistently different proportions of the emitted MTs throughout the measurement campaign: pinene-type, myrcene-type and limonene-type. Measurements showed a systematic diel variation in emissions typical of light and temperature-dependent, de novo-synthesized VOCs. The results demonstrated the feasibility of the FastGC/PTR-MS system for continuous measurements from dynamic chambers in the field, whereas further improvements would be necessary to lower the detection limit for ambient air measurements.

Agricultural activities highly contribute to atmospheric pollution, but the diversity and the magnitude of their emissions are still subject to large uncertainties. A field measurement campaign was conducted to characterize gaseous and particulate emissions from an experimental farm in France containing a sheep pen and a dairy stable. During the campaign, more than four hundred volatile organic compounds (VOCs) were characterized using an original combination of online and off-line measurements. Carbon dioxide (CO2) and ammonia (NH3) were the most concentrated compounds inside the buildings, followed by methanol, acetic acid and acetaldehyde. A CO2 mass balance model was used to estimate NH3 and VOC emission rates. To our knowledge, this study constitutes the first evaluation of emission rates for most of the identified VOCs. The measurements show that the dairy stable emitted more VOCs than the sheep pen. Despite strong VOC and NH3 emissions, the chemical composition of particles indicates that gaseous farm emissions do not affect the loading of fine particles inside the farm and is mainly explained by the low residence time inside the buildings. The experimental dataset obtained in this work will help to improve emissions inventories for agricultural activities.

Biogenic volatile organic compounds (BVOC) are mainly emitted from vegetation. However there is still little information on BVOC exchanges with crops. In this study we measured fluxes of BVOC from wheat, maize and rapeseed crops near Paris at the plant level during a full-week period for each species. We used dynamic automated chambers coupled to a Proton Transfer Reaction, Quadrupole ion guide, Time of Flight mass spectrometer (PTR-Qi-Tof-MS) instrument for online measurements of BVOC. Our results confirm the hypothesis that many unexplored compounds contribute to BVOC exchanges between crops and the atmosphere, although for all plant species methanol was dominating the emissions (55-85% of the sum of the BVOC exchanges fluxes on a mass basis) followed by acetone and acetaldehyde. The 10 most exchanged compounds, excluding methanol, contributed more than 50% of the summed fluxes and the 100 most exchanged contributed to more than 90%. The summed BVOC emission and deposition presented large interspecies variations, but limited antra-species variability, with a summed net flux of 0.11 +/- 0.02 mu gBVOC g(Dw)(-1) h(-1) for maize, 1.5 +/- 0.7 mu gBVOC g(DW)(-1) h(-1) for wheat, and 9.1 +/- 2.4 mu gBVOC g(DW)(-1) h(-1) for rapeseed. The 10 most emitted compounds were mostly emitted during the day and were correlated with both photosynthetically active radiation and temperature and anti-correlated with relative humidity. This study provides the first evaluation so far of the biosphere-atmosphere fluxes for several BVOC. In particular we provide a first evaluation of standard emission factor for isoprene and monoterpene for wheat and rapeseed at their respective growth stages. This study is however limited to a week period at a given stage for each species and at the plant level.