Atmos. Chem. Phys. Discuss., 9, 6451-6482, 2009
www.atmos-chem-phys-discuss.net/9/6451/2009/
doi:10.5194/acpd-9-6451-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
In-cloud processes of methacrolein under simulated conditions – Part 3: Hygroscopic and volatility properties of the formed Secondary Organic Aerosol
V. Michaud1, I. El Haddad2, Y. Liu2, K. Sellegri1, P. Laj1, P. Villani1, D. Picard1, N. Marchand2, and A. Monod2
1LaMP, CNRS – Université Blaise Pascal, 63117 Aubière Cedex, France
2LCP, CNRS-UMR 6264, Université de Provence, 3 Place Victor Hugo, case 29, 13003 Marseille, France

Abstract. The hygroscopic and volatility properties of SOA produced from the nebulization of solutions after aqueous phase photooxidation of methacrolein was experimentally studied in laboratory, using a Volatility-Hygroscopicity Tandem DMA (VHTDMA). The obtained SOA were 80% 100°C-volatile after 5 h of reaction and only 20% 100°C-volatile after 22 h of reaction. The Hygroscopic Growth Factor (HGF) of the SOA produced from the nebulization of solutions after aqueous-phase photooxidation of methacrolein is 1.34–1.43, which is significantly higher than the HGF of SOA formed by gas-phase phtooxidation of terpenes, usually found nearly hydrophobic. These hygroscopic properties were confirmed for SOA formed by the nebulization of the same solutions where NaCl was added. The hygroscopic properties of the cloud droplet residuals decrease with the reaction time, in parallel with the formation of more refractory compounds. This decrease was mainly attributed to the 250°C-refractive fraction (presumably representative of the highest molecular weigh compounds), evolved from moderately hygroscopic (HGF of 1.52) to less hygroscopic (HGF of 1.36). Oligomerization is suggested as a process responsible for the decrease of both volatility and hygroscopicity with time. The NaCl seeded experiments enabled us to show that 19±4 mg L−1 of SOA was produced after 9.5 h of reaction and 41±9 mg L−1 after 22 h of in-cloud reaction. Because more and more SOA is formed as the reaction time increases, our results show that the reaction products formed during the aqueous-phase OH-oxidation of methacrolein may play a major role in the properties of residual particles upon droplet's evaporation. Therefore, the specific physical properties of SOA produced during cloud processes should be taken into account for a global estimation of SOA and their atmospheric impacts.

Citation: Michaud, V., El Haddad, I., Liu, Y., Sellegri, K., Laj, P., Villani, P., Picard, D., Marchand, N., and Monod, A.: In-cloud processes of methacrolein under simulated conditions – Part 3: Hygroscopic and volatility properties of the formed Secondary Organic Aerosol, Atmos. Chem. Phys. Discuss., 9, 6451-6482, doi:10.5194/acpd-9-6451-2009, 2009.
 
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