10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

Abstract View


Photochemical Aging and Transformation of Dissolved Organic Matter in Atmospheric Aqueous Phase

QI ZHANG, Lu Yu, Wenqing Jiang, University of California, Davis

     Abstract Number: 1652
     Working Group: Aerosol Chemistry

Abstract
Dissolved organic matter (DOM) is a significant constituent of fog and cloud waters resulting from dissolution of water-soluble organic particles and gases. DOM can undergo aqueous reactions to form more oxidized and less volatile species, which can significantly influence ambient organic aerosol (OA) concentration and composition after water is evaporated from drops. Studying the reactions of DOM in atmospheric waters is thus important for understanding the aqueous-phase aging and processing of OA. In this study, fog waters collected in the Central Valley of California during winter are illuminated with simulated sunlight while the evolution of DOM composition is characterized using an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-AMS) and a total carbon analyzer. Over the course of illumination equivalent to several days of tropospheric aging, the mass concentration of DOMOA (i.e., low-volatility DOM in fog water) increases, along with a gradual increase of DOMOA oxidation. The nitrogen-to-carbon ratio (N/C) of DOMOA also increases, indicating the formation of organic nitrogen compounds as well. However, the organic carbon concentration in the fog water remain constant throughout the reaction period, indicating that the increase of DOMOA is fully attributed to functionalization reactions that incorporate oxygen- and nitrogen-containing functional groups into the molecules. In the meantime, since the average molecular weight of DOMOA appears to decrease during the reactions, fragmentation reactions also happen but do not lead to significant formation of VOCs. Analysis of the HR-AMS mass spectra of DOMOA using Positive matrix factorization (PMF) allows us to represent the aqueous aging of DOMOA as a linear combination of the dynamic variations of distinct factors. The mass spectra and the time series of the factors yield insights into the aqueous phase aging process of organic matter in atmospheric condensed phases.