Interannual variability of nitrogen oxides emissions from boreal fires in Siberia and Alaska during 1996-2011 as observed from space

Past studies suggest that forest fires contribute significantly to the formation of ozone in the troposphere. However, the emissions of ozone precursors from wildfires, and the mechanisms involved in ozone production from boreal fires, are very complicated. Moreover, an evaluation of the role of forest fires is prevented by the lack of direct observations of the ozone precursor, nitrogen oxides (NOx), and large uncertainties exist in the emissions inventories currently used for modelling. Acomprehensive understanding of the important processes and factors involving wildfires has thus been unobtainable. Wemade 16 year consistent analyses ofNOx emissions from boreal wildfires by using satellite observations of tropospheric nitrogen dioxides (NO2) from 1996 to 2011. Wereport substantial interannual variability of troposphericNO(2) originating from large boreal fires over Siberia in 1998, 2002, 2003, 2006, and 2008; and over Alaska in 2004, 2005, and 2009. Monthly comparisons ofNO2 enhancements with fire radiative power (FRP) show reasonably strong correlation, suggesting that FRP is a better proxy than burned area for boreal fireNOx emissions. Weprovide space-based constraints onNOx emission factors (EFs) for Siberian and Alaskan fires. Although the associated uncertainty is relatively large, the derived EFs fall into a in reasonably agreeable range with those previously determined by in situ ground-based and airborne observations over these regions.