This collaborative project addresses a newly recognized (aqueous) pathway for the formation of secondary organic aerosol (SOA) in the atmosphere. The poor understanding of SOA formation is a major source of uncertainty in predictions of atmospheric aerosol concentrations and properties that affect climate, visibility and health. Current models do not capture the magnitude, distribution and dynamics of measured organic aerosol concentrations, and smog chamber experiments form SOA that is substantially less oxygenated and, therefore, less hygroscopic than aged atmospheric organic aerosol. There is growing evidence that these and other atmospheric observations can be explained, at least in part, by multiphase SOA formation involving aqueous reactions in clouds, fogs and wet aerosols. When this process is included in models, predicted SOA formed through aqueous chemistry is comparable in magnitude to that formed through the traditional pathway (e.g., gas phase reaction and partitioning to particulate organic matter) in the northeastern United States and globally. Several types of atmospheric measurements also provide evidence for this process.
This project addresses the following questions: 1) Is aqueous SOA formation clearly observable in the field? 2) How does aqueous SOA formation influence the oxygen-to-carbon ratio of the organic aerosol? 3) How much of the observed aqueous SOA produced can be explained by known mechanisms? What precursors are important? 4) To what extent does SOA formation depend on light, liquid water, and organic matter? How much can be attributed to aqueous formation processes?
Field measurements will be conducted during the PEGASOS campaign in the Po Valley, Italy, where conditions are ideal for SOA formation through reactions in aerosol water. In conjunction with these field studies, controlled aqueous photooxidation experiments will be conducted in the laboratory with detailed chemical analysis and chemical modeling using 1) water-soluble (filtered) mixtures of compounds scrubbed from the ambient air, 2) collected (filtered) fog water, and 3) selected compounds identified as potential aqueous precursors based on project findings.
Broader Impacts: This work will further elucidate an important pathway for secondary organic aerosol formation and provide an assessment of the relative importance of this pathway in locations where conditions are favorable to SOA formation in wet aerosols and fogs. This project will provide a measurements database and a unique archive of characterized fog samples for use by other investigators. This research is designed to contribute ultimately to improved global/regional prediction of aerosol effects from precursor emissions. This project will facilitate the education of scientists. The planned K-12 outreach is designed to reach large numbers of students and to increase interest in and understanding of the process of scientific discovery by youth.
