Volume 12, No. 4, August 2012, Pages 503-514 PDF(452 KB)
Aerosol Optical Properties Observed at a Semi-Arid Rural Site in Northeastern China
Yunfei Wu1,2, Renjian Zhang1, Yifen Pu1, Leiming Zhang1,3, K.F. Ho4, Congbin Fu1,5
1 Key Laboratory of Regional Climate-Environment Research for Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
2 Graduate University of Chinese Academy of Sciences, Beijing 100049, China
3 Air Quality Research Division, Science and Technology Branch, Environment Canada, Toronto, Canada
4 School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China
5 School of Atmospheric Sciences, Nanjing University, Nanjing 210093, China
Continuous in situ measurements of aerosol optical properties have been conducted since March 2010 at a semi-arid rural site in Northeastern China - Tongyu (44.56°N, 122.92°N, elevation 151 m), a reference site of Coordinate Water and Energy cycle Observation Project (CEOP). Aerosol optical properties derived from the measurements during two spring seasons in 2010 and 2011 are analyzed and presented here. Mean values (and standard deviation) of light absorption coefficient (αab) and scattering coefficient (αsc) at 520 nm were 7.61 Mm–1 (6.17 Mm–1) and 89.22 Mm–1 (88.37 Mm–1), respectively, in spring of 2010, and were 7.01 Mm–1 (5.60 Mm–1) and 85.34 Mm–1 (116.11 Mm–1), respectively, in spring 2011. These values are lower than the majority of measurements made in other areas of China. The mean single scattering albedo (ω) was 0.90, greater than values found in some developed areas in China, indicating more scattering or less absorbing aerosols at Tongyu site. Mean values (and standard deviation) of the Ångström exponent of absorption (αab) were 1.61 (0.27) and 1.64 (0.28) for spring of 2010 and 2011, respectively, and of the scattering (αsc) were 1.48 (0.50) and 1.10 (0.50), respectively. The values of αab were higher than those of pure BC, implying the presence of other light absorbing materials having larger αab values. The moderate values of αsc indicated that considerable amount of coarse particles presented at Tongyu site. Distinct diurnal variations of aerosol optical properties were observed. ω, αab and αsc had nearly opposite diurnal variations compared to those of αab and αsc. Dust aerosols from the northwest and anthropogenic aerosols from the south were major sources contributing to the episodic aerosol events and thus, unusual aerosol optical properties, in spring at Tongyu site. High levels of PM2.5, if mainly caused by dust particles, do not necessarily introduce high values of αab and αsc.
Light absorption; Light scattering; Semi-arid area.