Inverse Modeling of Nitrogen Oxides Emissions from the 2010 Russian Wildfires by Using Satellite Measurements of Nitrogen Dioxide

Nitrogen oxides (NO_x) play a major role in the atmospheric oxidation processes leading to ozone and secondary organic aerosol formation in the lower atmosphere. Wildfires are one of the important sources of NO_x emissions; however, knowledge of NO_x emissions from fires is currently insufficient and available estimates provided by emission inventories have mostly not been validated against atmospheric measurements. Recent studies indicated that useful observational constraints to biomass burning (BB) NO_x emissions are provided by satellites measurements of nitrogen dioxide (NO₂), but available BB NO_x emission estimates inferred from such measurements involve quantitative assumptions regarding the atmospheric NO_x lifetime. In this study, we investigated NO_x emissions from the extreme wildfires that occurred in the European part of Russia in summer 2010. To this end, we analyzed tropospheric NO₂ retrievals from measurements performed by the OMI satellite instrument in the framework of an original inverse modeling method. A quantitative relationship between BB NO_x emissions and tropospheric NO₂ columns was simulated using the mesoscale CHIMERE chemistry transport model. Our analysis indicated that such a relationship depends strongly on BB emissions of volatile organic compounds and that a dependence of the effective NO_x lifetime on the NO_x fluxes can be essentially nonlinear. Our estimates of the total NO_x emissions in the study region are found to be at least 40% larger compared to the respective data from the GFASv1.0 and GFED4.1s global fire emission inventories.