Satellite constraints of nitrogen oxide (NOx) emissions from India based on OMI observations and WRF-Chem simulations

In this work, we map and develop for the first time an independent satellite constrained NOx emission inventory for India for 2005 using an inverse technique and iterative procedure. We used OMI tropospheric NO2 column retrievals over the Indian region, with tropospheric NO2 columns simulated by the WRF-Chem model using the INTEX-B emission inventory. We determined the local relationship between modeled emissions and tropospheric columns and iteratively apply this relationship to OMI observations to derive an optimized NOx emission inventory on a 0.5° × 0.5° grid. The optimized total NOx emissions for India amount to 1.9 TgN/y and agree within 25% with EDGARv4.1 and the INTEX-B estimate. Our top-down inventory captures many of the missing hotspots in the original inventory and suggests that the INTEX-B inventory overestimates emissions over the Western and Eastern Indo-Gangetic region and underestimates point sources. We further evaluate the effect of the top-down inventory on surface ozone, which clearly indicates significant changes in spatial distribution.