Drying-Induced Evaporation of Secondary Organic Aerosol during Summer

摘要

This study characterized the effect of drying on the concentration of atmospheric secondary organic aerosol (SOA). Simultaneous measurements of water-soluble organic carbon in the gas (WSOC_g) and particle (WSOC_p) phases were carried out in Baltimore, MD during the summertime. To investigate the effect of drying on SOA, the WSOC. measurement was alternated through an ambient channel (WSOC_p) and a "dried" channel (WSOC_(p,dry)) maintained at ～35% relative humidity (RH). The average man ratio between WSOC_(p,dry) and WSOC_p was 0.8S, showing that significant evaporation of the organic aerosol occurred due to drying. The average amount of evaporated water-soluble organic matter (WSOM = WSOC × 1.95) was 0.6 μg m~(-3); however, the maximum evaporated WSOM concentration exceeded 5 μg m~(-3), demonstrating the importance of this phenomenon. The systematic difference between ambient and dry channels indicates a significant and persistent source of aqueous SOA formed through reversible uptake processes. The wide-ranging implications of the work are discussed, and include: new insight into atmospheric SOA formation; impacts on particle measurement techniques; a newly identified bias in PM_(2.5) measurements using the EPA's Federal Reference and Equivalent Methods (FRM and FEM); atmospheric model evaluations; and the challenge in relating ground-based measurements to remote sensing of aerosol properties.