JULY 2003: Inventory of NO_x Emissions Constrained with Satellite Observations

The adjacent figure shows seasonal mean surface NO_x emissions for 1996-97 constrained with observations from the GOME satellite instrument. We retrieve tropospheric NO₂ columns from GOME to derive top-down constraints on NO_x emissions, and combine these with a priori information from a bottom-up emission inventory (with error weighting) to achieve an optimized a posteriori estimate of the global distribution of NO_x emissions. We use the GEOS-CHEM model to calculate the local relationship between GOME NO₂ columns and NO_x emissions as our top-down constraint. The derived NO_x emissions for industrial regions are aseasonal, despite large seasonal variations in NO₂ columns, providing confidence in the method. Our global a posteriori estimate for annual land surface NO_x emissions (37.7 Tg N yr^-1) agrees closely with the GEIA-based a priori (36.4) and with the EDGAR bottom-up inventory (36.6), but there are significant regional differences. A posteriori NO_x emissions are higher by 50-100% in the Po Valley, Tehran, and Riyadh urban areas, and by 25-35% in Japan and South Africa. Biomass burning emissions from India, central Africa, and Brazil are lower by up to 50%; soil NO_x emissions are appreciably higher in the western United States, the Sahel, and southern Europe. This work was led by Randall Martin. A full account is given in our in press manuscript Martin et al. [2003].