Analytical Chemistry Seminar

Analytical & Environmental Chemistry Division and Atmospheric Chemistry Program Seminar
Jointly sponsored by the Department of Chemistry and Biochemistry, CIRES, and the Environmental Program
Aerosol Liquid Water: A Valentine to the Clean Air Act
by Prof. Annmarie Carlton, Associate Professor, UC Irvine
Water is a ubiquitous and abundant component of atmospheric particles. It influences light scattering, the hydrological cycle, atmospheric chemistry, and secondary formation of particulate matter (PM) in the atmosphere. Despite the critical importance of aerosol liquid water, actual mass concentrations are not well documented in the literature. Routine air quality networks that measure particle mass [e.g., the U.S. Environmental Protection Agency’ s Interagency Monitoring of Protected Visual Environments(IMPROVE)] and most particle measurement techniques [e.g., the aerosol mass spectrometer (AMS)] remove water and other semivolatile compounds during sampling and/or during filter equilibration. Using speciated ion and meteorological data we estimate water mass concentrations to better understand the geospatial patterns and historical trends of aerosol liquid water in the context of improved air quality and recently noted reductions in particulate organic carbon (OC) mass. We find a decrease in aerosol water mass concentrations that is correlated with decreasing organic particle mass, for which we can provide a plausible mechanistic explanation. These findings are consistent with the hypotheses that aerosol liquid water facilitates formation of biogenic secondary organic aerosol (SOA) and that biogenically derived SOA is modulated in the presence of anthropogenic perturbations. Decreasing aerosol liquid water mass can be explained, in part, by environmental regulations aimed at reducing sulfur emissions to alleviate environmental problems associated with acid rain and inorganic particle mass, suggesting the Clean Air Act is more successful than accounted for.