Partitioning Phase Preference for Secondary Organic Aerosol in an Urban Atmosphere
WAYNE L. CHANG (1), Robert J. Griffin (2), Donald Dabdub (1)
(1) University of California, Irvine, (2) Rice University
Abstract Number: 315
Preference: Platform Presentation
Last modified: May 6, 2010
Working Group: Aerosol Chemistry
Secondary organic aerosol (SOA) comprises a significant portion of atmospheric particular matter (PM). The impact of PM on both human health and global climate has long been recognized. Despite its importance, there are still many unanswered questions regarding the formation and evolution of SOA in the atmosphere. Due to the complexity of ambient SOA interactions, numerical simulations often are used to assess the importance of individual SOA chemical and physical pathways observed in chamber experiments. This study utilizes a modeling approach to understand the preferred partitioning behavior of SOA species into aqueous or organic condensed phases. A statistical analysis of approximately 24,000 data values for each variable from a state-of-the-art 3-D airshed model is used in this work. Spatial and temporal distributions of fractions of SOA residing in the aqueous phase coupled with relevant meteorological parameters in the South Coast Air Basin of California will be presented. Typical values of fAQ within the basin near the surface range from 5 to 80%. Results show that the likelihood of large fAQ values is inversely proportional to the total SOA loading. Analysis of various meteorological parameters indicates that large fAQ values are predicted because modeled aqueous-phase SOA formation is less sensitive than that of organic-phase SOA to atmospheric conditions that are not conducive to SOA formation. There is a diurnal variation of fAQ near the surface: it tends to be larger during daytime hours than nighttime hours. Results also indicate that the largest fAQ values are simulated in layers above ground level at night. In summary, one must consider SOA in both organic and aqueous phases for proper regional and global SOA budget estimation.