Estimating NO2 dry deposition using satellite data in eastern China

The spatial and temporal characters of ground-level NO2 concentration over eastern China were retrieved from the monthly averaged tropospheric NO2 column densities from Global Ozone Monitoring Experiment (GOME, data used in this study are from April 1996 to December 2002) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY, data used in this study are from January 2003 to December 2011) measurements. Together with the NO2 concentration and the dry deposition velocity maps of eastern China, the fluxes of NO2 dry deposition were estimated for three specific regions. The results indicated that the surface NO2 concentration in eastern China increased dramatically from 1996 to 2011, and it showed distinct regional and seasonal variational characteristics. The highest concentration occurred in winter while the lowest occurred in summer. There was also variation in the spatial distribution with the peak value of NO2 concentration appearing in the plains of north China (R1), the Yangtze River delta (R2), and the Pearl River delta (R3). A sharp increase of NO2 concentration appeared in R1 and R2, while it was invariant or showed an obvious decrease in R3 during the period of 19962011. Furthermore, we compared the NO2 dry deposition fluxes estimated from the ground-level NO2 concentration and the dry deposition velocity of NO2 with the mass concentration of NO2 dry deposition that, measured from the control experiments and by consulting the published literature, showed a significant correlation (P<0.001) and had a high R value (R=0.73). The results also indicated that the NO2 dry deposition fluxes increased over eastern China, with a maximum value of 8.25kgNha1yr1 from 1996 to 2011 in R3, while the value was characterized by fluxes of less than 2.27kg Nha1yr1 in R2. When comparing the NO2 dry deposition over different land covers, the values distinctly peaked over artificial surfaces and evergreen forests, with maximum values of 10.07 and 9.49 kg N ha1 yr1 in R1, 5.05 and 4.94 kgNha1yr1 in R2, and 20.95 and 23.15 kgNha1yr1 in R3. However, the lowest value of NO2 dry deposition flux appeared over needleleaf forests, with 0.53, 0.24, and 1.29 kgNha1 yr1 for R1, R2, and R3, respectively.