AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Chemical Apportionment of Aerosol Optical Properties during the Asia-Pacific Economic Cooperation (APEC) Summit in Beijing
TINGTING HAN, Weiqi Xu, Chen Chen, Wei Du, Qingqing Wang, Zifa Wang, Ting Yang, Xingang Liu, Yele Sun, Inst. of Atmospheric Physics, Chinese Academy of Sciences
Abstract Number: 164 Working Group: Haze in China: Sources, Formation Mechanisms, and Current Challenges
Abstract The particle extinction was measured in-situ by a Cavity Attenuated Phase Shift extinction monitor along with size-resolved non-refractory submicron aerosol composition by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) at an urban site in Beijing from 15 October to 12 November 2014. The average extinction coefficient (b$_ext) and absorption coefficient (b$_ap) were 509.6±473.1 Mm$^-1 and 52.4±40.8 Mm$^-1, respectively, before APEC, which were more than twice higher than those observed during APEC when strict emission controls were implemented in Beijing and surrounding regions. The chemical composition and size distributions had significant changes during APEC, as a response, the mass scattering efficiency of PM$_1 was decreased from 5.0 to 3.7 during APEC. The empirical relationships between chemical composition and particle extinction were established using a multiple linear regression model. Our results showed the largest contribution of ammonium nitrate to particle extinction before and during APEC, accounting for 35.5% and 29.1%, respectively. This result highlights the important role of ammonium nitrate in the formation of severe haze episodes in this study. The contributions of primary and secondary OA (SOA) to particle extinction were also separated and quantified. The contribution of SOA to total particle extinction showed a clear decrease from 17.8% before APEC to 13.8% during APEC. In contrast, the POA extinction contribution increased from 12% to15.8%. These results suggested an enhanced role of POA in visibility degradation during APEC. Finally, a link of SSA and extinction with chemical composition, size distributions, and emission controls were established.