Characterization of aerosol optical properties, chemical composition and mixing states in the winter season in Shanghai, China

Yong Tang , Yuanlong Huang , Ling Li , Hong Chen , Jianmin Chen , Xin Yang , Song Gao , Deborah S. Gross


Received January 03, 2014,Revised April 11, 2014, Accepted , Available online December 22, 2014

Volume 26,2014,Pages 2412-2422

Physical and chemical properties of ambient aerosols at the single particle levelwere studied in Shanghai from December 22 to 28, 2009. A Cavity-Ring-Down Aerosol Extinction Spectrometer (CRD-AES) and a nephelometer were deployed to measure aerosol light extinction and scattering properties, respectively. An Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) was used to detect single particle sizes and chemical composition. Seven particle types were detected. Air parcels arrived at the sampling site fromthe vicinity of Shanghai untilmid-day of December 25, when they started to originate from North China. The aerosol extinction, scattering, and absorption coefficients all dropped sharply when this cold, clean air arrived. Aerosol particles changed from a highly aged type before thismeteorological shift to a relatively fresh type afterwards. The aerosol optical properties were dependent on the wind direction. Aerosols with high extinction coefficient and scattering Ångström exponent (SAE) were observed when the wind blew from the west and northwest, indicating that they were predominantly fine particles. Nitrate and ammoniumcorrelatedmost stronglywith the change in aerosol optical properties. In the elemental carbon/organic carbon (ECOC) particle type, the diurnal trends of single scattering albedo (SSA) and elemental carbon (EC) signal intensity had a negative correlation. We also found a negative correlation (r=-0.87) between high mass-OC particle number fraction and the SSA in a relatively clean period, suggesting that particulate aromatic components might play an important role in light absorption in urban areas.

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