Characterization of wildfire NO_x emissions using MODIS fire radiative power and OMI tropospheric NO₂ columns

Abstract. We use observations of fire radiative power (FRP) from the Moderate Resolution Imaging Spectroradiometer~(MODIS) and tropospheric NO₂ column measurements from the Ozone Monitoring Instrument (OMI) to derive NO₂ wildfire emission coefficients (g MJ⁻¹) for three land types over California and Nevada. Retrieved emission coefficients were 0.279±0.077, 0.342±0.053, and 0.696±0.088 g MJ⁻¹ NO₂ for forest, grass and shrub fuels, respectively. These emission coefficients reproduce ratios of emissions with fuel type reported previously using independent methods. However, the magnitude of these coefficients is lower than prior estimates. While it is possible that a negative bias in the OMI NO₂ retrieval over regions of active fire emissions is partly responsible, comparison with several other studies of fire emissions using satellite platforms indicates that current emission factors may overestimate the contributions of flaming combustion and underestimate the contributions of smoldering combustion to total fire emissions. Our results indicate that satellite data can provide an extensive characterization of the variability in fire NO_x emissions; 67 % of the variability in emissions in this region can be accounted for using an FRP-based parameterization.