No abstract

[1] In order to investigate the optical properties of atmospheric aerosol in the urban area of Beijing, in situ and remote measurements of particulate pollutants were conducted at an urban site ( , respectively. Average mass scattering efficiency of PM 10 and PM 2.5 particle were found to be 2.5 ± 1.1 and 3.4 ± 1.2 m 2 g À1 , respectively. Average single scattering albedo (SSA) of dry PM 10 was characterized to be 0.82 ± 0.09. It was found that SSA decreased to lower values of $0.75 during the relatively clean condition while it increased up to $0.86 during polluted condition mainly owing to the increases of ammonium sulfate, ammonium nitrate, and organic mass by carbon's contributions to PM mass concentrations. Pollution episodes in Beijing were strongly related to wind speed and wind direction. Stagnant weather conditions with southerly wind and low wind speed accelerated the accumulation of the pollutants in Beijing, which led to severe haze. It has been found that high PM 2.5 /AOT (aerosol optical thickness) ratio of 228.2 mg m À3 was observed when air mass was transported from western or northern China while significantly lower PM 2.5 /AOT of 107.6 mg m À3 was observed when it was affected mostly by local air pollutants in Beijing.

No abstract

No abstract