A study of the stageful characteristics and influencing factors of a long-lasting fog/haze event in Beijing

The meteorological influencing factors and aerosols characteristics of a long-lasting fog/haze event in Beijing during 3-8 November 2009 were analyzed using the high resolution observations. Significant stage characteristics are revealed during the process, in which haze dominated in the early stage, then fog and haze alternated in the middle stage, and at last haze reappears and gradually dissipates with the decreasing of relative humidity (RH) and PM2.5 concentration. The results show that it is RH and PM2.5 concentration to determine visibility in the process, but the impacts of these two also show a stage characteristics. When visibility is less than 1 km, RH is an important factor to visibility. In most of the period, PM2.5 concentration plays an important role in reducing visibility. Calculations from the three scenarios show that the control of PM2.5 concentration will be crucial role in improving visibility.