Bulk organic aerosol analysis by PTR-MS: an improved methodology for the determination of total organic mass, O:C and H:C ele- mental ratios and the average molecular formula

International audienceWe have recently shown in this journal (Müller et al., Anal. Chem. 2017, 89, 10889-10897) how a proton-transfer-reaction mass spectrometry (PTR-MS) analyzer measured particulate organic matter in urban atmospheres using the "Chemical Analysis of Aerosol Online" (CHARON) inlet. Our initial CHARON studies did not take into account fragmentation of protonated analyte molecules, which introduced a small but significant negative bias in the determination of bulk organic aerosol parameters. Herein, we studied the ionic fragmentation of 26 oxidized organic compounds typically found in atmospheric particles. This allowed us to derive a correction algorithm for the determination of the bulk organic mass concentration, m OA , the bulk-average hydrogen to carbon ratio, (H:C) bulk, the bulk-average oxygen-to-carbon, (O:C) bulk , and the bulk-average molecular formula, MF bulk. The correction algorithm was validated against AMS data using two sets of published data. Finally, we determined MF bulk of particles generated from the reaction of -pinene and ozone and compared and discussed the results in relation to the literature

Etude de la formation d'aérosols organiques secondaires par spectométrie de masse lors de l'ozonolyse de composés organiques volatils insatures

The understanding of secondary organic aerosols (SOA) is still incomplete, especially from the ozonolysis of unsaturated volatile organic compounds (VOC). The measurement of low volatility compounds involved in SOA formation is a challenge that the scientific community attempts to address. One of the objectives of this thesis work was the installation and use of a system for sampling and measuring the chemical composition of the aerosol by chemical ionization mass spectrometry (FIGAERO-CI-ToF-MS). This instrument has been used in the ozonolysis of unsaturated VOCs in the atmospheric simulation chamber HELIOS and the conditions for the formation of carboxylic acids and organosulfur compounds has been evaluated. The specific formation pathways of organosulfates (OS) have in addition been studied by injecting acidified seed particles. This study confirmed the low efficiency of the esterification of hydroxyl groups. Conversely, OS formation by epoxide ring opening is more efficient and increases with more acidic pH. In addition, the increase in relative humidity has a positive impact on the generation of carboxylic acids in the particulate phase.A second objective was the characterization of a system coupled to a proton transfer mass spectrometer (CHARON-PTR-ToF-MS) for collecting aerosols and measuring its chemical composition. The measurement of the fragmentation of 26 pure compounds in particulate phase allowed the development of a corrective procedure taking into account fragmentation process. This procedure was applied to the measurement of SOA generated by the ozonolysis of biogenic VOCs in an aerosol flow reactor. The volatility of the aerosol has been estimated using a thermodenuder installed downstream of the reactor. Taking into account fragmentation has greatly improved the agreement between the measured and the calculated volatility by several parametric equations.La compréhension de la formation des aérosols organiques secondaires (AOS) reste lacunaire, notamment lors de l’ozonolyse de composés organiques volatils (COV) insaturés. La mesure de composés de faible volatilité participant à la génération des AOS est un défi auquel la communauté scientifique tente de répondre. Un des objectifs de ce travail de thèse était l’installation et l’emploi d’un système d’échantillonnage et de mesure de la composition chimique de l’aérosol par spectrométrie de masse à ionisation chimique (FIGAERO-CI-ToF-MS). Cet instrument a été utilisé dans le cadre de l’ozonolyse de COV insaturés dans la chambre de simulation atmosphérique HELIOS et a permis d’évaluer les conditions de formation d’acides carboxyliques et de composés organosoufrés. Les voies de formation spécifiques des organosulfates (OS) ont par ailleurs été étudiées en injectant des particules d’ensemencement acidifiées. Cette étude a confirmé la faible efficacité de l’estérification des groupements hydroxyles. A l’inverse, la formation d’OS par ouverture de cycle époxyde est plus efficace et augmente à pH plus acide. Par ailleurs, l’augmentation de l’humidité relative a un impact positif sur la génération d’acides carboxyliques en phase particulaire.Un deuxième objectif était la caractérisation d’un système de collecte de l’aérosol et de mesure de sa composition chimique, couplé à un spectromètre de masse à transfert de protons (CHARON-PTR-ToF-MS). La mesure de la fragmentation de 26 composés purs en phase particulaire a permis le développement d’une procédure corrective tenant compte du phénomène de fragmentation. Cette procédure a été appliquée à la mesure d’AOS générés par l’ozonolyse de COV biogéniques en réacteur a écoulement. La volatilité de l’aérosol produit a été estimée par l’installation d’un tube thermodénudeur. La prise en compte de la fragmentation a grandement amélioré l’accord entre la mesure de la volatilité et son calcul par plusieurs équations paramétriques

Study of secondary organic aerosol formation by mass spectrometry from the ozonolysis of unsaturated volatile organic compounds

La compréhension de la formation des aérosols organiques secondaires (AOS) reste lacunaire, notamment lors de l’ozonolyse de composés organiques volatils (COV) insaturés. La mesure de composés de faible volatilité participant à la génération des AOS est un défi auquel la communauté scientifique tente de répondre. Un des objectifs de ce travail de thèse était l’installation et l’emploi d’un système d’échantillonnage et de mesure de la composition chimique de l’aérosol par spectrométrie de masse à ionisation chimique (FIGAERO-CI-ToF-MS). Cet instrument a été utilisé dans le cadre de l’ozonolyse de COV insaturés dans la chambre de simulation atmosphérique HELIOS et a permis d’évaluer les conditions de formation d’acides carboxyliques et de composés organosoufrés. Les voies de formation spécifiques des organosulfates (OS) ont par ailleurs été étudiées en injectant des particules d’ensemencement acidifiées. Cette étude a confirmé la faible efficacité de l’estérification des groupements hydroxyles. A l’inverse, la formation d’OS par ouverture de cycle époxyde est plus efficace et augmente à pH plus acide. Par ailleurs, l’augmentation de l’humidité relative a un impact positif sur la génération d’acides carboxyliques en phase particulaire.Un deuxième objectif était la caractérisation d’un système de collecte de l’aérosol et de mesure de sa composition chimique, couplé à un spectromètre de masse à transfert de protons (CHARON-PTR-ToF-MS). La mesure de la fragmentation de 26 composés purs en phase particulaire a permis le développement d’une procédure corrective tenant compte du phénomène de fragmentation. Cette procédure a été appliquée à la mesure d’AOS générés par l’ozonolyse de COV biogéniques en réacteur a écoulement. La volatilité de l’aérosol produit a été estimée par l’installation d’un tube thermodénudeur. La prise en compte de la fragmentation a grandement amélioré l’accord entre la mesure de la volatilité et son calcul par plusieurs équations paramétriques.The understanding of secondary organic aerosols (SOA) is still incomplete, especially from the ozonolysis of unsaturated volatile organic compounds (VOC). The measurement of low volatility compounds involved in SOA formation is a challenge that the scientific community attempts to address. One of the objectives of this thesis work was the installation and use of a system for sampling and measuring the chemical composition of the aerosol by chemical ionization mass spectrometry (FIGAERO-CI-ToF-MS). This instrument has been used in the ozonolysis of unsaturated VOCs in the atmospheric simulation chamber HELIOS and the conditions for the formation of carboxylic acids and organosulfur compounds has been evaluated. The specific formation pathways of organosulfates (OS) have in addition been studied by injecting acidified seed particles. This study confirmed the low efficiency of the esterification of hydroxyl groups. Conversely, OS formation by epoxide ring opening is more efficient and increases with more acidic pH. In addition, the increase in relative humidity has a positive impact on the generation of carboxylic acids in the particulate phase.A second objective was the characterization of a system coupled to a proton transfer mass spectrometer (CHARON-PTR-ToF-MS) for collecting aerosols and measuring its chemical composition. The measurement of the fragmentation of 26 pure compounds in particulate phase allowed the development of a corrective procedure taking into account fragmentation process. This procedure was applied to the measurement of SOA generated by the ozonolysis of biogenic VOCs in an aerosol flow reactor. The volatility of the aerosol has been estimated using a thermodenuder installed downstream of the reactor. Taking into account fragmentation has greatly improved the agreement between the measured and the calculated volatility by several parametric equations

Experimental and numerical investigation on aerosol emission in musical practice and efficiency of reduction means

Early in the Covid-19 pandemic, musical practices, especially singing and playing wind instruments, have been pointed out as having a high risk of SARS-CoV-2 virus transmission due to a high aerosol production. However, characterization of these emission sources was not consolidated. This study focuses on the generation of aerosols potentially carrying SARS-CoV-2 viruses and protective measures in the context of playing wind instruments and singing. Aerosol concentration reduction means are evaluated using aerosol measurements in clean room and Computational Fluid Dynamics. Measurements at the bell of a clarinet and in front of singers are performed with or without a protection (bell cover for clarinet and surgical mask for singers). Numerical results on clarinet suggest that most of the supermicron (1 μm) particles are trapped on the walls of the instruments, which act as a filter, depending on fingerings which lead to different lateral toneholes positions (closed or opened) changing the frequency of sound. Experimental results are consistent since almost only submicron particles contribute to the measured number concentration during playing clarinet. First of all, the high inter and intra-individuals variability is highlighted, with high coefficients of variation. This study highlights the impact of fingerings and on the generated particles and the efficiency of protections such as bell cover (from 3 to 100 times), depending on the played note and players. Results for singers show that surgical masks significantly reduce the aerosol concentration (from 8 to 170 times), which is also correlated with sound level

The atmospheric impact of Monoterpene ozonolysis intermediates: rate constant and secondary organic aerosol formation within SO2 oxidation

International audienc

The atmospheric impact of Monoterpene ozonolysis intermediates: rate constant and secondary organic aerosol formation within SO2 oxidation

International audienc

Chamber studies of the ozonolysis of several alkenes: gas-phase products and particle formation induced by SO2 oxidation

International audienc

Chamber studies of the ozonolysis of several alkenes: gas-phase products and particle formation induced by SO2 oxidation

International audienc

Atmospheric chamber measurements of H2SO4: characterization of formation and loss rates during the ozonolysis and aerosol formation studies

International audienceSulphuric acid, H2SO4, has been identified to play major role in atmospheric new particle formation and in subsequent particle growth. The oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) initiated by the reaction with the hydroxyl radicals (OH) is assumed to be the dominant formation pathway of sulfuric acid (H2SO4) in the troposphere. It has been suggested in the recent years that the reactions of Criegee Intermediates (CIs) with SO2 may also contribute to the H2SO4 formation, although the significance of this pathway compared to the reaction of OH with SO2 is still under discussion. As the ozonolysis of anthropogenic and biogenic terpenes emitted into the atmosphere may represent an important source of OH and CIs a better understanding of the ozonolysis mechanism in relation to the H2SO4 formation is required. In this study, we present the results obtained during the investigation of the ozonolysis of several unsaturated volatile organic compounds, including tetramethylethylene, α-pinene and limonene, using a newly constructed large atmospheric simulation chamber, HELIOS (ICARE-CNRS, Orléans, France). The HELIOS facility consists of a large outdoor simulation chamber (volume of 90 m3) equipped with a wide range of in-situ on-line and off-line analytical instrumentation (FTIR, PTR-TOF-MS, GC-MS, CIMS (OH and H2SO4), SMPS, Figaero-API-TOF-CIMS, HCHO monitor and others). The results of kinetic and mechanistic studies of the reactions of different CIs with SO2 induced by the ozonolysis of the studied VOCs under different conditions will be presented. The H2SO4 loss on the Teflon chamber wall and by the aerosol uptake were characterized using direct H2SO4 and particle measurements. Keywords: ozonolysis, Criegee Intermediate, sulfur dioxide, sulfuric acid, HELIO

Atmospheric chamber measurements of H2SO4: characterization of formation and loss rates during the ozonolysis and aerosol formation studies

International audienceSulphuric acid, H2SO4, has been identified to play major role in atmospheric new particle formation and in subsequent particle growth. The oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) initiated by the reaction with the hydroxyl radicals (OH) is assumed to be the dominant formation pathway of sulfuric acid (H2SO4) in the troposphere. It has been suggested in the recent years that the reactions of Criegee Intermediates (CIs) with SO2 may also contribute to the H2SO4 formation, although the significance of this pathway compared to the reaction of OH with SO2 is still under discussion. As the ozonolysis of anthropogenic and biogenic terpenes emitted into the atmosphere may represent an important source of OH and CIs a better understanding of the ozonolysis mechanism in relation to the H2SO4 formation is required. In this study, we present the results obtained during the investigation of the ozonolysis of several unsaturated volatile organic compounds, including tetramethylethylene, α-pinene and limonene, using a newly constructed large atmospheric simulation chamber, HELIOS (ICARE-CNRS, Orléans, France). The HELIOS facility consists of a large outdoor simulation chamber (volume of 90 m3) equipped with a wide range of in-situ on-line and off-line analytical instrumentation (FTIR, PTR-TOF-MS, GC-MS, CIMS (OH and H2SO4), SMPS, Figaero-API-TOF-CIMS, HCHO monitor and others). The results of kinetic and mechanistic studies of the reactions of different CIs with SO2 induced by the ozonolysis of the studied VOCs under different conditions will be presented. The H2SO4 loss on the Teflon chamber wall and by the aerosol uptake were characterized using direct H2SO4 and particle measurements. Keywords: ozonolysis, Criegee Intermediate, sulfur dioxide, sulfuric acid, HELIO