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

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.