Reactions in Atmospheric Particles and Drops
Historically, much attention has been paid to the gas-phase chemistry of the atmosphere and relatively little has been focused on reactions occurring in/on atmospheric particles and drops. But these particle and drop reactions can be important because they can: modify the chemical, physical, radiative, and toxicological properties of particles; act as sources or sinks of reactive gases; and participate in the biogeochemical cycling of important elements.

Our research in this area has looked both at the photoformation of oxidants in drops and particles as well as the transformations of specific compounds or classes of compounds. For example, we have examined the formation of hydroxyl radical (•OH), singlet molecular oxygen (¹O₂*), and hydrogen peroxide (H₂O₂) in cloud and fog drops and sea-salt particles. We have also characterized how these oxidants react with species such as organic compounds, organic nitrogen species, and halides (chloride and bromide) to make oxidized (and in some cases, reactive) products. For example, we are investigating sunlight-initiated reactions within sea-salt particles that form •OH and, in turn, produce halogen radicals and reactive halogens such as Br₂, which can alter gas-phase chemistry in marine areas. We are also examining how reactions of organic compounds in cloud and fog drops can lead to the formation of secondary organic aerosol, i.e., low-volatility compounds that remain as particles after the drops evaporate.