The validation of air quality during 2015 World Championships and Parade in Beijing and near region based on satellite observations

Environmental satellite observations were used to evaluate the effect of emission control measures on the changes of air pollutants in Beijing and its surroundings during the 2015 World Championships and Parade (WCP) held in Beijing. Compared to the past three years (2012-2014) in the same period, nitrogen oxides (NO2) and sulfur oxides (SO2) tropospheric vertical column densities (VCD) in 2015 were found to exhibit almost significant reductions over the North China Plain, suggesting the effectiveness of the national policy on NO2 and SO2 emission reduction during the important events. During the WCP period (Aug. 20 - Sept. 4), AOD was found reduced the most in Beijing, followed by Tianjin and Hebei province. However, air quality plummeted during the after-WCP period (Sept. 5 - 20), which was largely related to the lifting of local and regional joint emission control measures. By applying correlation coefficients of NO2, SO2, AOD during August 4 to September 20 of latest two years between Beijing with surroundings (Zhangjiakou represents northwest trajectories and Chengde represents northeast trajectories, Tianjin for southeast, and Shijiazhuang for southwest), during the study period in 2015, areas impacting Beijing evidently shrank and were limited within north on Beijing, suggesting evident effects of intense emission perturbations on lowering the extent of regional transport. We also analyze the meteorological conditions. During the study period in 2015, the relative humidity is 60%-80% in Beijing, low RH lead better visibility if there is less haze. The North China Plain is near of high pressure from its north. Sea high pressure has been completely removed. Southward pressure gradient force and weak north and northeast winds blocked the pollution transport from southern and western part of industrial area Hebei, Shanxi and Shandong province). Cold air masses push southward weakly. Under this condition, it is beneficial to the removal of pollutants. Due to Strict emission reduction measures and favorable meteorological conditions, during the WCP, air quality in Beijing kept ideal level.