Abstract
Abstract. The gas phase oxidation of organic species is a multigenerational process involving a large number of secondary compounds. Most secondary organic species are water-soluble multifunctional oxygenated molecules. The fully explicit chemical mechanism GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) is used to describe the oxidation of organics in the gas phase and their mass transfer to the aqueous phase. The oxidation of three hydrocarbons of atmospheric interest (isoprene, octane and α-pinene) is investigated for various NOx conditions. The simulated oxidative trajectories are examined in a new two dimensional space defined by the mean oxidation state and the solubility. The amount of dissolved organic matter was found to be very low (yield less than 2% on carbon atom basis) under a water content typical of deliquescent aerosols. For cloud water content, 50% (isoprene oxidation) to 70% (octane oxidation) of the carbon atoms are found in the aqueous phase after the removal of the parent hydrocarbons for low NOx conditions. For high NOx conditions, this ratio is only 5% in the isoprene oxidation case, but remains large for α-pinene and octane oxidation cases (40% and 60%, respectively). Although the model does not yet include chemical reactions in the aqueous phase, much of this dissolved organic matter should be processed in cloud drops and modify both oxidation rates and the speciation of organic species.
Highlights
The atmospheric aqueous phase includes water in clouds and fogs droplets and deliquescent particles
50 % to 70 % of the carbon atoms are found in the aqueous phase after the removal of the parent hydrocarbons for low NOx conditions
This study describes the first stage in the development of such a modeling tool and examines the phase partitioning of organic species produced during the gas phase oxidation of hydrocarbons
Summary
The atmospheric aqueous phase includes water in clouds and fogs droplets and deliquescent particles. As experimental studies inside clouds are scarce and very difficult to set up (Crahan et al, 2004; Herrmann et al, 2005; Sorooshian et al, 2007), most of the organics clouds chemistry studies have been performed based on modeling approaches These models usually represent the condensed phase as a single well mixed aqueous phase in which organic species undergo oxidation. Atmospheric processing of long chain hydrocarbons is expected to lead to the production of highly water soluble multifunctional organics in a few oxidation steps (e.g. van Pinxteren et al, 2005; Mazzoleni et al, 2010). The fraction of these compounds that could be subjected to aqueous phase processing has yet to be determined. The simulated carbon budget and the composition of the gas and aqueous phase are explored in detail
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