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AOSC Departmental Seminar
November 19, 2015

Aerosol water: now you see it, now you don’t!

Ann Marie Carlton
Department of Environmental Sciences, Rutgers University

Summertime aerosol optical thickness (AOT) in the Southeast U.S. is sharply enhanced (2-3 times) compared to wintertime AOT. This seasonal pattern is unique to the Southeast U.S. and is of particular interest because temperatures there have not warmed over the past 100 years, contrasting with global trends and other U.S. regions. Some investigators speculate that anthropogenic and biogenic emissions combine to form a cooling haze over the Southeast U.S., however recent analysis of organic aerosol surface mass measurements do not support this hypothesis. In this work, we attempt to reconcile the spatial and temporal distribution of AOT over the U.S. with surface mass measurements by examining trends in particle-phase liquid water, an aerosol constituent that effectively scatters radiation and is removed from aerosols in mass measurements at routine surface monitoring sites. We employ the thermodynamic model ISORROPIA (v2.1) to estimate surface and aloft aerosol water mass concentrations at locations of Interagency Monitoring of Protected Visual Environments (IMPROVE) sites using measured speciated ion mass concentrations and NCEP North American Regional Reanalysis (NARR) meteorological data. Our findings suggest similarity between spatial trends in aerosol water in the U.S. and previously published AOT satellite data. These aerosol water results provide a plausible explanation for the geographical and seasonal patterns in AOT, and reconcile AOT with surface mass networks.