Secondary organic aerosol formation from isoprene photooxidation during cloud condensation–evaporation cycles

L Brégonzio-Rozier,F Siekmann,H L Dewitt,A Monod,J.-F Doussin,V Michoud,E Pangui,M Cazaunau,C Giorio,A Tapparo,A Gratien,B Temime-Roussel,S B Morales

doi:10.5194/acp-16-1747-2016

Abstract

Abstract. The impact of cloud events on isoprene secondary organic aerosol (SOA) formation has been studied from an isoprene ∕ NOx ∕ light system in an atmospheric simulation chamber. It was shown that the presence of a liquid water cloud leads to a faster and higher SOA formation than under dry conditions. When a cloud is generated early in the photooxidation reaction, before any SOA formation has occurred, a fast SOA formation is observed with mass yields ranging from 0.002 to 0.004. These yields are 2 and 4 times higher than those observed under dry conditions. When the cloud is generated at a later photooxidation stage, after isoprene SOA is stabilized at its maximum mass concentration, a rapid increase (by a factor of 2 or higher) of the SOA mass concentration is observed. The SOA chemical composition is influenced by cloud generation: the additional SOA formed during cloud events is composed of both organics and nitrate containing species. This SOA formation can be linked to the dissolution of water soluble volatile organic compounds (VOCs) in the aqueous phase and to further aqueous phase reactions. Cloud-induced SOA formation is experimentally demonstrated in this study, thus highlighting the importance of aqueous multiphase systems in atmospheric SOA formation estimations.

Highlights

Tropospheric fine aerosol particles are known to cause several environmental impacts, including adverse health effects and radiative forcing on climate (Hallquist et al, 2009; IPCC, 2013)
The comparison between diphasic and triphasic experiments suggests that the presence of a reacting mixture that underwent more oxidation steps, and composed of more oxidized compounds did not play a significant role in the amount of aqSOA produced
It was observed that a single and relatively short cloud condensation cycle in the presence of irradiation led to a significant aqSOA mass yield (0.002–0.004) with values between 2 and 4 times higher than that observed for isoprene photooxidation experiments carried out under dry conditions (Brégonzio-Rozier et al, 2015)

Summary

Introduction

Tropospheric fine aerosol particles are known to cause several environmental impacts, including adverse health effects and radiative forcing on climate (Hallquist et al, 2009; IPCC, 2013). SOA formation results from the atmospheric oxidation of volatile organic compounds (VOCs) leading to the formation of less volatile oxidation products that can undergo gas to particle conversion. Some of these oxidized species contain acid, hydroxyl and/or aldehyde functional groups that increase their water solubility, and explain their presence in cloud droplets (Herckes et al, 2013; Herrmann et al, 2015). Clouds cover ∼ 70 % of the earth surface on average (Stubenrauch et al, 2013; Wylie et al, 2005) and only ∼ 10 % of them precipitate while the remaining ∼ 90 % dissipate, leading to evaporation of volatile compounds and condensation of lower-volatility species (Herrmann et al, 2015). Aqueous-phase chemical pathways lead to enhanced production of acids, such as oxalic acid, (Carlton et al, 2007, 2006), and oligomers that have been observed

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Conclusion