8 research outputs found
Réactivité des terpÚnes avec le radical nitrate : études cinétique et mécanistique en chambres de simulation atmosphérique
Biogenic volatile organic compounds (BVOC) are strongly emitted by forests and crops in the atmosphere. They are very reactive towards nitrate radical, the main tropospheric oxidant during the night, and play a key role in atmospheric chemistry. These reactions lead to the formation of a variety of functionalized products (organic nitrates, carbonyl compounds ...) and to large amounts of secondary organic aerosols. Organic nitrates are the main nitrogen oxides reservoir. They directly influence reactive nitrogen and ozone budgets. Secondary organic aerosol has direct and indirect impacts on climate, due to its formation, its optical and hygroscopic properties and its chemical composition. The aim of this work is to understand these processes at the molecular scale, through kinetic and mechanistic studies of NO3 radical oxidation of several BVOCs.Kinetic and mechanistic studies have been performed for three monoterpenes ((C10H16), Îł- and α-terpinene and terpinolene) and one sesquiterpene ((C15H24), ÎČ-caryophyllene) in atmospheric simulation chambers. These compounds have been chosen to highlight the influence of their chemical structures on their reactivities and to fill the lack of experimental data about their chemistry in the literature.For the kinetic part, rate constants have been measured with both relative and absolute methods. Due to their high reactivities, this study has requiered the development on the simulation chamber of an IBB-CEAS ((Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) analysis pathway to measure nitrate radical at the ppt level. Mechanistic studies have been also conducted to identify and quantify the main reaction products. Organic nitrates and SOA yields have been calculated. Detected products allowed proposing reaction mechanisms.Les composĂ©s organiques volatils biogĂ©niques (COVB) sont fortement Ă©mis dans lâatmosphĂšre par les forĂȘts et les cultures. TrĂšs rĂ©actifs vis-Ă -vis du radical nitrate NO3, principal oxydant nocturne dans la troposphĂšre, ils ont une importance majeure dans la chimie atmosphĂ©rique. En effet, cette rĂ©action mĂšne Ă la formation dâun large panel de produits de rĂ©action en phase gazeuse fonctionnalisĂ©s (nitrates organiques, composĂ©s carbonylĂ©s, ...) et une large fraction dâaĂ©rosols organiques secondaires. Les nitrates organiques constituent des espĂšces rĂ©servoirs dâoxydes dâazote dans lâatmosphĂšre et influencent directement le bilan dâazote rĂ©actif et ainsi les niveaux dâozone. LâaĂ©rosol organique secondaire, de par sa formation, ses propriĂ©tĂ©s optiques et hygroscopiques ainsi et sa composition chimique a un impact direct et indirect sur le climat. Ce travail a pour but la comprĂ©hension de ces processus Ă lâĂ©chelle molĂ©culaire Ă travers une Ă©tude cinĂ©tique et mĂ©canistique des rĂ©actions dâoxydation de plusieurs COVB par le radical NO3.Ainsi, les rĂ©actions dâoxydation par le radical NO3 de trois monoterpĂšnes ((C10H16), Îł- et α-terpinĂšne et le terpinolĂšne) et un sesquiterpĂšne ((C15H24), le ÎČ-caryophyllĂšne) ont Ă©tĂ© invesitguĂ©es en chambre de simulation atmosphĂ©rique. Les composĂ©s ont Ă©tĂ© choisis dâune part pour mettre en Ă©vidence lâinfluence de leur structure chimique sur leur rĂ©activitĂ© et dâautre part, pour combler les manques de donnĂ©es expĂ©rimentales dans la littĂ©rature sur la chimie de ces composĂ©s.Pour la partie cinĂ©tique, les constantes de vitesse ont Ă©tĂ© mesurĂ©es Ă la fois par la mĂ©thode de cinĂ©tique absolue et par celle de cinĂ©tique relative. Les rĂ©actions chimiques Ă©tudiĂ©es Ă©tant trĂšs rapides, cette Ă©tude a nĂ©cessitĂ© au prĂ©alable le dĂ©veloppement sur la chambre de simulation atmosphĂ©rique dâune voie dâanalyse spectroscopique IBB-CEAS (Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) pour la mesure des radicaux nitrates dans la gamme du ppt. Des Ă©tudes mĂ©canistiques ont Ă©galement Ă©tĂ© menĂ©es afin dâidentifier et de quantifier les principaux produits de rĂ©action. Les rendements de nitrates organiques, dâAOS ont Ă©tĂ© calculĂ©s. Les produits dĂ©tectĂ©s ont permis dâĂ©tablir des mĂ©canismes rĂ©actionnels
Reactivity of terpenes with nitrate radical : kinetic and mechanistic studies in atmospheric simulation chambers
Les composĂ©s organiques volatils biogĂ©niques (COVB) sont fortement Ă©mis dans lâatmosphĂšre par les forĂȘts et les cultures. TrĂšs rĂ©actifs vis-Ă -vis du radical nitrate NO3, principal oxydant nocturne dans la troposphĂšre, ils ont une importance majeure dans la chimie atmosphĂ©rique. En effet, cette rĂ©action mĂšne Ă la formation dâun large panel de produits de rĂ©action en phase gazeuse fonctionnalisĂ©s (nitrates organiques, composĂ©s carbonylĂ©s, ...) et une large fraction dâaĂ©rosols organiques secondaires. Les nitrates organiques constituent des espĂšces rĂ©servoirs dâoxydes dâazote dans lâatmosphĂšre et influencent directement le bilan dâazote rĂ©actif et ainsi les niveaux dâozone. LâaĂ©rosol organique secondaire, de par sa formation, ses propriĂ©tĂ©s optiques et hygroscopiques ainsi et sa composition chimique a un impact direct et indirect sur le climat. Ce travail a pour but la comprĂ©hension de ces processus Ă lâĂ©chelle molĂ©culaire Ă travers une Ă©tude cinĂ©tique et mĂ©canistique des rĂ©actions dâoxydation de plusieurs COVB par le radical NO3.Ainsi, les rĂ©actions dâoxydation par le radical NO3 de trois monoterpĂšnes ((C10H16), Îł- et α-terpinĂšne et le terpinolĂšne) et un sesquiterpĂšne ((C15H24), le ÎČ-caryophyllĂšne) ont Ă©tĂ© invesitguĂ©es en chambre de simulation atmosphĂ©rique. Les composĂ©s ont Ă©tĂ© choisis dâune part pour mettre en Ă©vidence lâinfluence de leur structure chimique sur leur rĂ©activitĂ© et dâautre part, pour combler les manques de donnĂ©es expĂ©rimentales dans la littĂ©rature sur la chimie de ces composĂ©s.Pour la partie cinĂ©tique, les constantes de vitesse ont Ă©tĂ© mesurĂ©es Ă la fois par la mĂ©thode de cinĂ©tique absolue et par celle de cinĂ©tique relative. Les rĂ©actions chimiques Ă©tudiĂ©es Ă©tant trĂšs rapides, cette Ă©tude a nĂ©cessitĂ© au prĂ©alable le dĂ©veloppement sur la chambre de simulation atmosphĂ©rique dâune voie dâanalyse spectroscopique IBB-CEAS (Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) pour la mesure des radicaux nitrates dans la gamme du ppt. Des Ă©tudes mĂ©canistiques ont Ă©galement Ă©tĂ© menĂ©es afin dâidentifier et de quantifier les principaux produits de rĂ©action. Les rendements de nitrates organiques, dâAOS ont Ă©tĂ© calculĂ©s. Les produits dĂ©tectĂ©s ont permis dâĂ©tablir des mĂ©canismes rĂ©actionnels.Biogenic volatile organic compounds (BVOC) are strongly emitted by forests and crops in the atmosphere. They are very reactive towards nitrate radical, the main tropospheric oxidant during the night, and play a key role in atmospheric chemistry. These reactions lead to the formation of a variety of functionalized products (organic nitrates, carbonyl compounds ...) and to large amounts of secondary organic aerosols. Organic nitrates are the main nitrogen oxides reservoir. They directly influence reactive nitrogen and ozone budgets. Secondary organic aerosol has direct and indirect impacts on climate, due to its formation, its optical and hygroscopic properties and its chemical composition. The aim of this work is to understand these processes at the molecular scale, through kinetic and mechanistic studies of NO3 radical oxidation of several BVOCs.Kinetic and mechanistic studies have been performed for three monoterpenes ((C10H16), Îł- and α-terpinene and terpinolene) and one sesquiterpene ((C15H24), ÎČ-caryophyllene) in atmospheric simulation chambers. These compounds have been chosen to highlight the influence of their chemical structures on their reactivities and to fill the lack of experimental data about their chemistry in the literature.For the kinetic part, rate constants have been measured with both relative and absolute methods. Due to their high reactivities, this study has requiered the development on the simulation chamber of an IBB-CEAS ((Incoherent Broad Band Cavity Enhanced Absorption Spectroscopy) analysis pathway to measure nitrate radical at the ppt level. Mechanistic studies have been also conducted to identify and quantify the main reaction products. Organic nitrates and SOA yields have been calculated. Detected products allowed proposing reaction mechanisms
A comparative and experimental study of the reactivity with nitrate radical of two terpenes: alpha-terpinene and gamma-terpinene
International audienceAbstract. Biogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. During the night, they react very rapidly with the nitrate radical (NO3), leading to the formation of a variety of functionalized products including organic nitrates and to large amounts of secondary organic aerosols (SOAs). Organic nitrates (ONs) have been shown not only to play a key role in the transport of reactive nitrogen and consequently in the ozone budget but also to be important components of the total organic-aerosol mass, while SOAs are known to play a direct and indirect role in the climate. However, the reactivity of BVOCs with NO3 remains poorly studied. The aim of this work is to provide new kinetic and mechanistic data for two monoterpenes (C10H16), α- and Îł-terpinene, through experiments in simulation chambers. These two compounds, which have very similar chemical structures, have been chosen in order not only to overcome the lack of experimental data but also to highlight the influence of the chemical structure on the reactivity. Rate constants have been measured using both relative and absolute methods. They were found to be (1.2±0.5)Ă10-10 and (2.9±1.1)Ă10-11âcm3âmoleculeâ1âsâ1 for α- and Îł-terpinene respectively. Mechanistic studies have also been conducted in order to identify and quantify the main reaction products. Total organic nitrate and SOA yields have been determined. While organic nitrate formation yields appear to be similar, SOA yields exhibit large differences with Îł-terpinene being a much more efficient precursor of aerosols. In order to provide explanations for this difference, chemical analysis of the gas-phase products was performed at the molecular scale. Detected products allowed for proposing chemical mechanisms and providing explanations through peroxy and alkoxy reaction pathways
An experimental study of the reactivity of terpinolene and ÎČ-caryophyllene with the nitrate radical
International audienceBiogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. They can rapidly react with the nitrate radical (NO3) during the nighttime to form a number of functionalized products. Among them, organic nitrates (ONs) have been shown to behave as reservoirs of reactive nitrogen and consequently influence the ozone budget and secondary organic aerosols (SOAs), which are known to have a direct and indirect effect on the radiative balance and thus on climate. Nevertheless, BVOC + NO3 reactions remain poorly understood. Thus, the primary purpose of this study is to furnish new kinetic and mechanistic data for one monoterpene (C10H16), terpinolene, and one sesquiterpene (C15H24), ÎČ-caryophyllene, using simulation chamber experiments. These two compounds have been chosen in order to complete the few experimental data existing in the literature. Rate constants have been measured using both relative and absolute methods. They have been measured to be (6.0 ± 3.8) Ă10-11 and (1.8 ± 1.4) Ă10-11 cm3 molec.â1 sâ1 for terpinolene and ÎČ-caryophyllene respectively. Mechanistic studies have also been conducted in order to identify and quantify the main reaction products. Total organic nitrates and SOA yields have been determined. Both terpenes appear to be major ON precursors in both gas and particle phases with formation yields of 69 % for terpinolene and 79 % for ÎČ-caryophyllene respectively. They are also major SOA precursors, with maximum SOA yields of around 60 % for terpinolene and 90 % for ÎČ-caryophyllene. In order to support these observations, chemical analyses of the gas-phase products were performed at the molecular scale using a proton transfer reaction-time-of-flight-mass spectrometer (PTR-ToF-MS) and FTIR. Detected products allowed proposing chemical mechanisms and providing explanations through peroxy and alkoxy reaction pathways
Implementation of an incoherent broadband cavity-enhanced absorption spectroscopy technique in an atmospheric simulation chamber for in situ NO<sub>3</sub> monitoring: characterization and validation for kinetic studies
International audienceAbstract. An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for the in situ monitoring of NO3 radicals at the parts per trillion level in the CSA simulation chamber (at LISA). The technique couples an incoherent broadband light source centered at 662ânm with a high-finesse optical cavity made of two highly reflecting mirrors. The optical cavity which has an effective length of 82âcm allows for up to 3âkm of effective absorption and a high sensitivity for NO3 detection (up to 6âppt for an integration time of 10âs). This technique also allows for NO2 monitoring (up to 9âppb for an integration time of 10âs). Here, we present the experimental setup as well as tests for its characterization and validation. The validation tests include an intercomparison with another independent technique (Fourier-transform infrared, FTIR) and the absolute rate determination for the reaction trans-2-buteneâ+âNO3, which is already well documented in the literature. The value of (4.13â±â0.45)âĂâ10â13âcm3âmoleculeâ1âsâ1 has been found, which is in good agreement with previous determinations. From these experiments, optimal operation conditions are proposed. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (VOCs; with rate constants up to 10â10âcm3âmoleculeâ1âsâ1)
Implementation of an incoherent broadband cavity-enhanced absorption spectroscopy technique in an atmospheric simulation chamber for in situ NO<sub>3</sub> monitoring: characterization and validation for kinetic studies
International audienceAbstract. An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for the in situ monitoring of NO3 radicals at the parts per trillion level in the CSA simulation chamber (at LISA). The technique couples an incoherent broadband light source centered at 662ânm with a high-finesse optical cavity made of two highly reflecting mirrors. The optical cavity which has an effective length of 82âcm allows for up to 3âkm of effective absorption and a high sensitivity for NO3 detection (up to 6âppt for an integration time of 10âs). This technique also allows for NO2 monitoring (up to 9âppb for an integration time of 10âs). Here, we present the experimental setup as well as tests for its characterization and validation. The validation tests include an intercomparison with another independent technique (Fourier-transform infrared, FTIR) and the absolute rate determination for the reaction trans-2-buteneâ+âNO3, which is already well documented in the literature. The value of (4.13â±â0.45)âĂâ10â13âcm3âmoleculeâ1âsâ1 has been found, which is in good agreement with previous determinations. From these experiments, optimal operation conditions are proposed. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (VOCs; with rate constants up to 10â10âcm3âmoleculeâ1âsâ1)
Nighttime chemistry of biomass burning emissions in urban areas: A dual mobile chamber study
International audienceResidential biomass burning for heating purposes is an important source of air pollutants during winter. Here we test the hypothesis that significant secondary organic aerosol production can take place even during winter nights through oxidation of the emitted organic vapors by the nitrate (NO3) radical produced during the reaction of ozone and nitrogen oxides. We use a mobile dual smog chamber system which allows the study of chemical aging of ambient air against a control reference. Ambient urban air sampled during a wintertime campaign during nighttime periods with high concentrations of biomass burning emissions was used as the starting point for the aging experiments. Biomass burning organic aerosol (OA) was, on average, 70 % of the total OA at the beginning of our experiments. Ozone was added in the perturbed chamber to simulate mixing with background air (and subsequent NO3 radical production and aging), while the second chamber was used as a reference. Following the injection of ozone, rapid OA formation was observed in all experiments, leading to increases in the OA concentration by 20 %-70 %. The oxygen-to-carbon ratio of the OA increased on average by 50 %, and the mass spectra of the produced OA was quite similar to the oxidized OA mass spectra reported during winter in urban areas. Furthermore, good correlation was found for the OA mass spectra between the ambient-derived emissions in this study and the nocturnal aged laboratory-derived biomass burning emissions from previous work. Concentrations of NO3 radicals as high as 25 ppt (parts per trillion) were measured in the perturbed chamber, with an accompanying production of 0.1-3.2 ”g mâ3 of organic nitrate in the aerosol phase. Organic nitrate represented approximately 10 % of the mass of the secondary OA formed. These results strongly indicate that the OA in biomass burning plumes can chemically evolve rapidly even during wintertime periods with low photochemical activity
A performance evaluation and inter-laboratory comparison of community face coverings media in the context of covid-19 pandemic
International audienceDuring the recent pandemic of SARS-CoV-2, and as a reaction to the worldwide shortage of surgical masks, several countries have introduced new types of masks named âcommunity face coveringâ (CoFC). To ensure the quality of such devices and their relevance to slow down the virus spreading, a quick reaction of the certification organisms was necessary to fix the minimal acceptable performances requirements. Moreover, many laboratories involved in the aerosol research field have been asked to perform tests in a quick time according to (CEN, 2020) proposed by the European committee for standardization. This specification imposes a minimal air permeability of 96 L.m-2.s-1 and a minimal filtration efficiency of 70% for 3 ”m diameter particles. In the present article, an intercomparison of efficiency and permeability measured by 3 testing laboratories has been performed. Results are in good agreement considering the heterogeneity of the considered material samples (within 27 % in terms of filtration efficiency and less than 20 % in terms of permeability). On this basis, an analysis of 233 materials made of woven, non-woven and mixed fibrous material has been done in terms of filtration efficiency and air permeability. For some of them, measurements have been performed for 0.2 ”m, 1 ”m and 3 ”m particle diameters. As expected, no deterministic correlation could be determinated to link these efficiencies to the permeability of the considered samples; however, a trend could be identified. The same exercise has been conducted to link the filtration efficiency measured at 3 ”m to the filtration for lower diameters. Finally, a discussion on the kind of material that is the most relevant to manufacture âcommunity face coveringâ (CoFC) supported by spectral filtration efficiency (from 0.02 ”m to 3 ”m) is proposed