Chemical Composition and Light Extinction Contribution of PM2.5 in Urban Beijing for a 1-Year Period

Huanbo Wang, Mi Tian, Xinghua Li, Qing Chang, Junji Cao, Fumo Yang, Yongliang Ma, Kebin He
2015 Aerosol and Air Quality Research  
Daily PM 2.5 samples were collected in Beijing across four consecutive seasons from June 2012 to April 2013. Major water-soluble inorganic ions, carbonaceous species and elements were analyzed to investigate their temporal variations and evaluate their contributions to visibility impairment over different seasons and under different pollution levels. The mass concentrations of PM 2.5 ranged from 4.3 to 592.4 µg m -3 , with an annual average of 112.4 ± 94.4 µg m -3 . The predominant components
more » ... minant components of PM 2.5 were secondary inorganic ions (NH 4 + , NO 3 and SO 4 2-) and carbonaceous compounds, which accounted for 45.9% and 24.1% of the total PM 2.5 mass, respectively. Distinct seasonal variation was observed in the mass concentrations and chemical components of PM 2.5 . The average mass concentrations of PM 2.5 were the highest in winter, followed by spring, and lowest in autumn. Light extinction coefficients (b ext ) were discussed over four seasons. (NH 4 ) 2 SO 4 was the largest contributor (28.8%) to b ext , followed by NH 4 NO 3 (24.4%), organic matter (19.5%), elemental carbon (7.4%), and coarse mass (7.2%), while fine soil, sea salt, NO 2 and Rayleigh made minor contributions, together accounting for 12.7% of b ext . During the polluted periods, the contributions of (NH 4 ) 2 SO 4 and NH 4 NO 3 to b ext increased dramatically. Therefore, in addition to control primary particulate emissions, the reduction of their precursors like SO 2 , NO x and NH 3 could effectively improve air quality and visibility in Beijing.
doi:10.4209/aaqr.2015.04.0257 fatcat:yrxrvjaeebezvdhypws7zaqe4a