March 2007: Seasonal variability of NO_x emissions over east China constrained by satellite observations: Implications for combustion and microbial sources

We use observations of tropospheric column densities of NO₂ obtained from the GOME instrument for a 3-year period (1997, 1998, and 2000) to derive average seasonal variations in surface emissions of NOx from east China (100^oE -- 123^oE, 20^oN -- 42^oN). The retr ieval allows for zonal variations in the contribution of the stratosphere to the NO₂ column and removes a bias of ±10% on the seasonality of retrieved columns introduced by cloud screening. The top-down inventory is constructed using an inversion approach with GEOS-Chem model and combined subsequently with the a priori inventory to develop an a posteriori inventory. The contribution of background NO₂ arising from non-surface sources (lightning) and long-range transport of emissions originating outside of east China is accounted for in the inversion. The a posteriori estimate of overall emissions for east China, 4.66 Tg N/yr (±30% uncertainty), is 33% higher than the a priori value. Based on multiple constraints on the spatial and seasonal variations of combustion and microbial processes, the a posteriori inventory is partitioned among emissions from biomass burning, fuel combustion, and microbial activity (or soil emissions).