The trend,seasonal cycle,and sources of tropospheric NO2 over China during 1997–2006 based on satellite measurement

The characteristics of spatial and temporal distribution of tropospheric NO₂ column density concentration over China are presented, on the basis of measurements from the satellite instruments GOME and SCIAMACHY. From these observations, monthly averaged tropospheric NO₂ variations are determined for the period of 1997 to 2006. The trend and seasonal cycle are also investigated. The possible source of tropospheric NO₂ over megacity area is discussed in this paper. The results show a large growth of tropospheric NO₂ over eastern China, especially above the industrial areas with a fast economical growth, such as, Yangtze Rive Delta region and Pearl River Delta region because of the prominent anthropogenic activity. There is a rapid increase of tropospheric NO₂ over megacities in China. For instance, Shanghai had a linear significant increase in NO₂ columns of ∼20% per year (reference year 1997) in the period of 1997–2006, which is the rapidest increase among all the selected cities. The seasonal pattern of the NO₂ concentration shows a difference between the east and west in China. In the eastern part of China, an expected winter maximum in seasonal cycle is found because of the prominent anthropogenic activity and meteorological conditions. In the western part this cycle shows a NO₂ maximum in summer time, which is attributed to natural emissions, especially soil emissions and lightning. A quickly increasing vehicle population may contribute to the increase of tropospheric NO₂ over megacities in China for the remarkable correlation for vehicle population with tropospheric NO₂. Supported by the ESA-MOST “Drag-star” Program (Grant No. 2005AA 132031XZ07) the National Basic Research Program of China “973” Project (Grant Nos. 2005CB422200x and 2006CB403702) and the Special Project for Climatic Change From Chinese Meteorological Administration (Grant No. CCSF2007-11)