AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Characterization of Chemical Composition of Fog Water and Interstitial Aerosol in the Central Valley of California: Influence of Aqueous Chemistry
HWAJIN KIM, Xinlei Ge, Jianzhong Xu, Yele Sun, Youliang Wang, Pierre Herckes, Qi Zhang, University of California, Davis
Abstract Number: 509 Working Group: Aerosol Chemistry
Abstract A measurement study was conducted in the Central Valley (Fresno) of California in January 2010, during which radiation fog events were frequently observed. Fog plays important roles in atmospheric chemistry by scavenging aerosol particles and trace gases and serving as a medium for various aqueous-phase reactions. Understanding the effects of fog on the microphysical and chemical processing of aerosol particles requires detailed information on their chemical composition. In this study, we characterized the chemical composition of fog water and interstitial aerosol particles to study the effects of fog processing on aerosol properties. Fog water samples were collected during the 2010 Fresno campaigns with a Caltech Active Strand Cloud water Collector (CASCC) while interstitial submicron aerosols were characterized in real time with an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a Scanning Mobility Particle Sizer (SMPS). The fog water samples were later analyzed using the HR-ToF-AMS, ion chromatography, and a total carbon analyzer. The chemical composition and characteristics of interstitial particles during the fog events were compared to those of dissolved inorganic and organic matter in fog waters. Our results indicate that aqueous phase chemistry modifies the chemical composition of condensed phase species significantly. In general, the Central Valley fog water is composed of a higher fraction of nitrate and organics than in interstitial aerosol. We also found that sulfate is formed more efficiently in fog water although its contribution to total mass is relatively low. The high resolution mass spectra of dissolved organic matter (DOM) in fog water and those of oxygenated organic aerosols (OOA) derived from multivariate analysis of the HR-ToF-AMS spectra are highly correlated (R$^2 = 0.92). A main distinct difference between fog DOM and OOA is the substantially higher N/C ratio (~3.8 times) in the fog water, mainly due to the presence of the C$_xH$_yN$_2$^+ family ions. By comparing with previous investigations and NIST mass spectra, we propose that the main source of nitrogen compounds is imidazole. Details and the environmental implications of results will be discussed.