AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
The Relationship of Hygroscopicity Parameter of Organic Aerosols to Their Oxidation Level
FAN MEI, Jian Wang, Qi Zhang, Jose-Luis Jimenez, Shan Zhou, Ari Setyan, Patrick Hayes, Amber Ortega, Jianzhong Xu, Jonathan Taylor, James Allan, Pacific Northwest National Laboratory
Abstract Number: 270 Working Group: Urban Aerosols
Abstract Atmospheric aerosols strongly influence the global energy budget by scattering and absorbing sunlight (direct effects) and by changing the microphysical structure, lifetime, and coverage of clouds (indirect effects). Currently, the indirect effects of aerosols remain the most uncertain components in forcing of climate change over the industrial period. This large uncertainty is in part due to our incomplete understanding of the ability of aerosol particles to form cloud droplets under climatically relevant supersaturations. The physical and chemical properties of organic aerosols (OA) are highly complex, due to complicated atmospheric processes, and making their characterization challenging.
During three field campaigns, size-resolved cloud condensation nuclei (CCN) spectrum and aerosol chemical composition were characterized, at an urban supersite (Pasadena, CA, CalNex-LA in 2010), and two urban downwind supersites (Cool, CA, CARES in 2010 and Upton, NY, ALC-IOP in 2011). At west coast sites, monodispersed aerosol particles were first classified using a differential mobility analyzer at sizes ranging from 25 to 320 nm. The activation efficiency of the classified aerosol, defined as the ratio of its CCN concentration (characterized by a DMT CCN counter) to total CN concentration (measured by a condensation particle counter, TSI 3771), is derived as a function of both particle size and supersaturation, which ranges from 0.08% to 0.39% during CalNex-LA and 0.15% to 0.45% during CARES. At east coast site, the characterized size range focused on 70-250 nm and the supersaturation range was from 0.11% to 0.78%. Aerosol chemical composition was characterized using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS).
At three sites, the overall hygroscopicity of particles (κCCN, Petters and Kreidenweis, 2007, ACP) is derived from the size-resolved CCN measurements and ranges from 0.15 to 0.35 under the measured supersaturations. Positive matrix factorization (PMF) analyses of HR-ToF-AMS measurements are carried out and the organics O:C ratios are examined in a relatively wide range (0.3-0.7). Based on the particle hygroscopicity and aerosol chemical composition, the organics hygroscopicity (κOrg) is also derived. And we will examine the correlation between organic aerosol hygroscopicity and oxidation level and compare them to other laboratory studies.