In-cloud processes of methacrolein under simulated conditions – Part 2: Formation of secondary organic aerosol

The fate of methacrolein in cloud evapo-condensation cycles was experimentally investigated. To this end, aqueous-phase reactions of methacrolein with OH radicals were performed (as described in Liu et al., 2009), and the obtained solutions were then nebulized and dried into a mixing chamber. ESI-MS and ESI-MS/MS analyses of the aqueous phase composition denoted the formation of high molecular weight multifunctional products containing hydroxyl, carbonyl and carboxylic acid moieties. The time profiles of these products suggest that their formation can imply radical pathways. These high molecular weight organic products are certainly responsible for the formation of secondary organic aerosol (SOA) observed during the nebulization experiments. The size, number and mass concentration of these particles increased significantly with the reaction time: after 22 h of reaction, the aerosol mass concentration was about three orders of magnitude higher than the initial aerosol quantity. The evaluated SOA yield ranged from 2 to 12%. These yields were confirmed by another estimation method based on the hygroscopic and volatility properties of the obtained SOA measured and reported by Michaud et al. (2009). These results provide, for the first time to our knowledge, strong experimental evidence that cloud processes can act, through photooxidation reactions, as important contributors to secondary organic aerosol formation in the troposphere

UV absorption cross-sections of a series of vinyl ethers

UV absorption cross-sections of six vinyl ethers (ethyl vinyl ether, 1,4-butanediol divinyl ether, isobutyl vinyl ether, cyclohexyl vinyl ether, 4-hydroxybutylvinyl ether and diethyleneglycol divinyl ether) have been determined in the gas phase between 190 and 230 nm at 303 ± 2 K and pressures up to the corresponding saturation vapor pressures. The main band maxima of the vinyl ethers are below 200 nm with values under 8 × 10-17 cm2 molecule-1. The absorption vanishes above 225 nm with values of σ smaller than 1 × 10-21 cm2 molecule-1. Weak, overlaying vibrational progressions with spacings of 1400 cm-1 are observed for the alkyl vinyl ethers and are less pronounced for vinyl ethers with an extra O atom. Shifts of the positions and intensities are discussed on the basis of the differences in the chemical structure of this series. © 2009 Elsevier B.V. All rights reserved.Fil: Nieto Gligorovski, L. I. University of Bayreuth; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Gligorovsky, S.. Universités d’Aix-Marseille; Francia. Centre National de la Recherche Scientifique; FranciaFil: Romano, Rosana Mariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Della Vedova, Carlos Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Zetsch, C.. Fraunhofer Institute For Toxicology And Experimental Medicine Item; Alemania. University of Bayreuth; Alemani

In-cloud processes of methacrolein under simulated conditions - Part 1: Aqueous phase photooxidation

International audienceThe photooxidation of methacrolein was studied in the aqueous phase under simulated cloud droplet conditions. The obtained rate constant of OH-oxidation of methacrolein at 6 degrees C in unbuffered solutions was 5.8(+/- 0.9)x10(9) M(-1) s(-1). The measured rate coefficient is consistent with OH-addition on the C=C bond. This was confirmed by the mechanism established on the study of the reaction products (at 25 degrees C in unbuffered solutions) where methylglyoxal, formaldehyde, hydroxyacetone and acetic acid/acetate were the main reaction products. An upper limit for the total carbon yield was estimated to range from 53 to 85%, indicating that some reaction products remain unidentified. A possible source of this mismatch is the formation of higher molecular weight compounds as primary reaction products which are presented in El Haddad et al. (2009) and Michaud et al. (2009)