AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Chemical and Physical Properties of Aerosols in Regional Air Masses and the Free Troposphere over the Western U.S.
SHAN ZHOU, Sonya Collier, Daniel Jaffe, Qi Zhang, University of California, Davis
Abstract Number: 444 Working Group: Remote and Regional Atmospheric Aerosols
Abstract Understanding the properties and lifecycle processes of aerosols in regional air masses and the free troposphere (FT) is crucial for constraining the climate impacts of aerosols on a global scale. In this study, characteristics of regional and FT aerosols in the western US were studied using a high-resolution time-of-flight aerosol mass spectrometer deployed at the Mount Bachelor Observatory (MBO; 2763 m a.s.l.) in central Oregon in summer 2013. In the absence of wildfire influence, the average (± 1σ) concentration of non-refractory submicrometer aerosol (NR-PM1) at MBO was 2.8 (± 2.8) µg m-3 and 84% of the mass was organic. Organic aerosols (OA) showed clear diurnal variations driven by the boundary layer (BL) dynamics with significantly higher concentrations occurring during daytime, upslope conditions. NR-PM1 contained a higher mass fraction of sulfate and was frequently acidic at night when MBO resided in the FT. OA in the FT was highly oxidized (O/C ~ 1.17) with low volatility. In contrast, OA associated with BL air masses had an average O/C of 0.67 and appeared to be semivolatile. The significant compositional and physical differences observed between FT and BL aerosols may have important implications for understanding the climate effects of regional background aerosols.