AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Evaluating the Degree of Oxygenation of Organic Aerosols During Foggy Days and Hazy Days in Springtime in Hong Kong Using High-Resolution Time-of-Flight Aerosol Mass Spectrometry (HR-ToF-AMS)
Yong J. Li, BERTO LEE, Chak K. Chan, Hong Kong University of Science and Technology
Abstract Number: 232 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The role of aqueous-phase chemistry in the formation of secondary organic aerosols is still poorly constrained. Here we present results on the effects of fine particle liquid water content (LWC$_(fp)) on the degree of oxygenation of organic aerosols (OA) based on high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) measurements made at a coastal site in Hong Kong during springtime. Data from two foggy weeks and one hazy week were chosen for analysis. The degree of oxygenation of OA, as indicated by several parameters including f44 (Ng et al., 2010), O:C and H:C ratios (Heald et al., 2010), and the carbon oxidation state (Kroll et al., 2011) was evaluated against odd oxygen concentration, relative humidity, LWC$_(fp), ionic strength, ratios of measured to predicted NH$_4, and in-situ pH. Results showed that for hazy week, the high concentration of OA and the high degree of oxygenation were mainly due to gas-phase oxidation. During the foggy days with low photochemical activities, the degree of oxygenation of OA was as high as that in hazy days, suggesting the important role of aqueous-phase chemistry in SOA formation. However, the evolution of OA behaved quite differently for the two foggy periods. The first foggy week in late April and early May had more LWC$_(fp) and lower particle acidity, and the OA had more semi-volatile oxygenated organic aerosols (SV-OOA) as resolved by positive matrix factorization (PMF). The second foggy week in mid-May had lower LWC$_(fp)and produced more low-volatility oxygenated organic aerosols (LV-OOA).
References
Heald et al., Geophys. Res. Lett., 37, L08803, 2010.
Kroll et al., Nature Chem., 3, 133-139, 2011.
Ng et al., Atmos. Chem. Phys., 10, 4625-4641, 2010.
Acknowledgement
This work was supported by the University Grants Committee (SEG-HKUST07) and the Environmental Conservation Funds (ECF) of Hong Kong (ECWW09EG04).