First Concurrent Observations of NO 2 and CO 2 From Power Plant Plumes by Airborne Remote Sensing

Combined NO 2 and CO 2 observations have the potential to constrain the identification of the locations and strength of urban CO 2 emissions, in particular, point sources such as power plants. We report the first results of airborne spectroscopic NO 2 and CO 2 observations over an urban area in Japan in February 2018. Inversed emission rates of two stacks of the coal‐fired power plant for CO 2 showed relatively good agreement with those estimated by a bottom‐up inventory—the Regional Emission inventory in ASia (REAS) v3.1—within −7% to 40% because the plume shapes were well identified due to constraint by NO 2 measurements. The estimated NO x emission rates showed discrepancies more than 80% with those estimated by the REAS v3.1, mainly due to the uncertainties in activity data and emission factors, or in the greatly varying NO/NO 2 ratios in fresh plumes, which warrant further investigations when estimating NO x emissions from satellite NO 2 observations on km‐scales.