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 1996–2011. 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 8.25 kg N ha⁻¹ yr⁻¹ from 1996 to 2011 in R3, while the value was characterized by fluxes of less than 2.27 kg N ha⁻¹ yr⁻¹ 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 ha⁻¹ yr⁻¹ in R1, 5.05 and 4.94 kg N ha⁻¹ yr⁻¹ in R2, and 20.95 and 23.15 kg N ha⁻¹ yr⁻¹ in R3. However, the lowest value of NO₂ dry deposition flux appeared over needleleaf forests, with 0.53, 0.24, and 1.29 kg N ha⁻¹ yr⁻¹ for R1, R2, and R3, respectively.