Insight into wintertime aerosol characteristics over Beijing

• Wintertime Aerosol characteristics over Beijing urban area were obtained.
• Monthly mean aerosol optical depth in the northern China had its minimum in winter.
• Wind dependence of aerosol optical properties was analyzed.
• Wintertime Beijing haze episodes were induced by local pollution emissions.

Aerosol particle pollution in northern China has crucial impact on regional and global climate. The monthly mean aerosol optical depth (AOD) at 550 nm in the northern China had its minimum in winter. Surface measurements of aerosol microphysical and optical properties over the Beijing urban area from December 3, 2011 to January 1, 2012 are presented here. The aim of this study was to evaluate wintertime aerosol characteristics, which were impacted by wind and relative humidity. The following mean values were observed: scattering coefficient (293±283 Mm−1, 1 Mm−1=10−6 m−1), absorption coefficient (136±125 Mm−1), backscattering ratio (0.15±0.02), single scattering albedo (0.65±0.08), at 550 nm, and scattering Angstrom exponent (2.01±0.22), with mean relative humidity of (47±24)%. Wintertime values of scattering and absorption coefficients had wind dependence, showing that high values occurred with calm winds while the dilution effect of strong winds was obtained for wind speed larger than 4 m s−1. Based on air mass backward trajectories, wintertime haze episodes in Beijing were induced by local-pollution emissions, whereas clear periods were dominated by air masses from clean, continental, northwestern areas. Our study indicates that the main challenge to improve wintertime air quality in Beijing is to control local emissions of particulate pollution.