Satellite constraints of nitrogen oxide (NO_x) 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 NO_x emission inventory for India for 2005 using an inverse technique and iterative procedure. We used OMI tropospheric NO ₂ column retrievals over the Indian region, with tropospheric NO ₂ 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 NO_x emission inventory on a 0.5°×0.5° grid. The optimized total NO_x 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.