Estimation of CO₂ and NO_X emissions using the divergence method applied to pseudo satellite observations

Abstract

A method based on the divergence theorem was developed to estimate emissions from high-frequency and high-horizontal-resolution satellite observations of atmospheric trace gases (NO₂ and CO₂), by accounting for the expected performance of the upcoming TANSO-3 / Global Observing SATellite for Greenhouse gases and Water cycle (GOSAT-GW). Pseudo satellite observations to which the divergence method was applied were constructed from atmospheric chemistry transport model simulations over the Kanto region with a 1-km horizontal resolution. Observational errors were then added as normal distributions with the standard deviations of 1.8 ppm for CO₂ total column dry-air mole fraction (XCO₂) and 3×10¹⁵ molecules/cm² for NO₂ tropospheric column density (NO₂VCD). The results showed that our central emission estimates for the Kashima Industrial Zone were within 10-24 % of the true values for CO₂ and NO_X, confirming the performance of the method. Uncertainties in the emission estimates propagated by observational errors (noise) were evaluated to be ±32 % and ±2 % for CO₂ and NO_X emissions of 16.6 MtCO₂/year and 25 ktNO_X/year, respectively, after averaging over 31 ideal observations, expected to occur within a 3-month period at best for GOSAT-GW.