AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
The Rise and Fall of Organic Matter in Clouds and Fogs: The Transition from Functionalization to Fragmentation
JEFFREY COLLETT, Misha Schurman, Alexandra Boris, Taehyoung Lee, Denise Napolitano, Pierre Herckes, Colorado State University
Abstract Number: 386 Working Group: There Must be Something in the Water: Cloud, Fog and Aerosol Aqueous Chemistry for Aerosol Production
Abstract Clouds and fogs play an important role as processors of many chemical species in the atmosphere. Particle scavenging followed by direct deposition or incorporation into precipitation represents an important atmospheric cleansing mechanism. Uptake of soluble gases followed by reaction in cloud/fog droplets can be an important source of secondary organic aerosol (SOA), while OA can also be “consumed” in clouds through chemical fragmentation to smaller, more volatile products that volatilize back to the gas phase. Here we provide an overview of research examining the processing of atmospheric organic matter by clouds and fogs in California, S. Korea, and China. Cloud and fog water were collected and analyzed for total organic carbon and a suite of organic acids that are often viewed as indicators of atmospheric aging of organics. Laboratory photooxidation studies were conducted on authentic cloud water samples using ultraviolet light and H2O2 to produce hydroxyl radical. Organic matter composition was followed during aging using on-line ESI-ToF-MS, offline IC, and direct atomization of aged cloud water followed by evaporation of resulting droplets and on-line drop residue measurements using an AMS. These experiments reveal functionalization and fragmentation regimes, where the organic aerosol from evaporated cloud drops respectively increases or decreases. Production of carbonyls and carboxylic acids is observed. The time to transition from overall organic matter functionalization to fragmentation appears to depend on the amount of organic matter available in the cloud/fog water, presumably reflecting altered competition for available oxidants. Overall, the rate of aqueous SOA production in studied cloud water decreases as oxygenation increases, with organic mass loss beginning at consistent values of f44 > 0.23 ± 0.05 and O:C > 0.61 ± 0.05. We hypothesize that there may be a parameterizable ‘peak oxidation level’ for cloud water above which functional group fragmentation is dominant.