Change of NO2 column density over Beijing from satellite measurement during the Beijing 2008 Olympic Games

The effect of the air quality ensuring measures for the Beijing 2008 Olympic Games in reducing air pollution during the game period is assessed using the tropospheric NO2 column density retrieved from Ozone Monitoring Instrument onboard AURA satellite. The basic method of the assessment is the comparison of the NO2 column densities during the game period with that during the corresponding period of 2005-2007 for the Beijing area, and the comparison among Beijing and neighbouring cities Tianjin and Tangshan, which are of similar situation in air pollution of NO2 in recent years. The images of tropospheric NO2 column densities over Northern China during the Beijing 2008 Olympic Games show the remarkable effect of the air quality ensuring measures in reducing NO2 pollution: the tropospheric NO2 column density in Beijing is much lower than that in Tianjin and Tangshan, while there were very similar values in the three large cities during the same period of the last three years. About 40% reduction in tropospheric NO2 column density over the Beijing area is obtained from the assessment during July to August, 2008, a key period of air quality ensuring measures for the Beijing 2008 Olympic Games.