Optical properties of atmospheric aerosols obtained by in situ and remote measurements during 2006 Campaign of Air Quality Research in Beijing (CAREBeijing-2006)

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 (39.98 degrees N, 116.35 degrees E, similar to 20 m above ground level) in Beijing during the Campaign of Air Quality Research in Beijing (CAREBeijing) campaign from 16 August to 10 September 2006. During the intensive measurement period, average PM2.5 mass concentration and light extinction coefficient (b(ext)) were measured to be 102.1 +/- 55.0 mu g m(-3) and 880.7 +/- 685.9 Mm(-1), respectively. Average mass scattering efficiency of PM10 and PM2.5 particle were found to be 2.5 +/- 1.1 and 3.4 +/- 1.2 m(2) g(-1), respectively. Average single scattering albedo (SSA) of dry PM10 was characterized to be 0.82 +/- 0.09. It was found that SSA decreased to lower values of similar to 0.75 during the relatively clean condition while it increased up to similar 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 PM2.5/AOT (aerosol optical thickness) ratio of 228.2 mu g m(-3) was observed when air mass was transported from western or northern China while significantly lower PM2.5/AOT of 107.6 mu g m(-3) was observed when it was affected mostly by local air pollutants in Beijing.