Speciation of Organic Matter in Fog Droplets: How Far are We from Mass Closure?

Fog and cloud chemistry have been studied for decades with research accelerating in the last 20 years. Aqueous sulfur oxidation has received particular attention due to the important contributions of clouds and fogs to the atmospheric sulfur cycle. In recent years organic compounds in fog and cloud drops begun to receive significant attention. Most studies have focused on a few, especially toxic compounds, leaving the majority of organic matter unidentified and uncharacterized. Consequently, little is known about processing of carbonaceous material by fogs and clouds or the creation of secondary organic aerosol by in-cloud reactions of gas phase organic species. Here we assemble all the information on organic compounds acquired during a recent field study conducted in Fresno in California’s Central Valley, to assess what fraction of the total organic matter in fog droplets is characterized. Backgroun