Variations and photochemical transformations of atmospheric constituents in North China

To study air pollution and chemical transformation in North China, annual and seasonal variations of the concentrations of atmospheric constituents were analyzed for four representative sites in three different types of regions (two agricultural, Beijing and surroundings, atmospheric background) in North China during 2005–2015. Satellite-derived vertical column densities (VCDs) of NO2, SO2, O3, HCHO, and aerosol optical depth (AOD) over the four sites were used together with ground-based radiation and meteorological measurements at each site and, at one of them (Xinglong), ground-based observations of NO2, SO2, O3 and PM2.5 concentrations. The temporal variations of UV loss in the atmosphere and VCDs of NO2, SO2, O3 and HCHO were investigated together with the relations between these. Based on the analysis, a photochemical link relating the production of PM2.5 and O3 in North China was proposed and confirmed. In particular the role of volatile organic compounds (VOCs) in chemical and photochemical reactions is found to be prominent in the summer. Suggestions for air pollution control in North China are given, e.g., to reduce anthropogenic VOC emissions and to prevent artificial enhancements of biogenic VOC emissions.