East Asian methane emissions inferred from high-resolution inversions of GOSAT and TROPOMI observations: a comparative and evaluative analysis

Abstract. We apply atmospheric methane column retrievals from two different satellite instruments (GOSAT and TROPOMI) to a regional inversion framework to quantify East Asian methane emissions for 2019 at 0.5° × 0.625° horizontal resolution. The goal is to assess if GOSAT (relatively mature but sparse) and TROPOMI (new and dense) observations inform consistent methane emissions from East Asia. Comparison of the results from the two inversions show similar correction patterns to the prior inventory in Central North China, Central South China, Northeast China, and Bangladesh, with less than 2.7 Tg a−1 differences in regional posterior emissions. The two inversions, however, disagree over some important regions particularly in northern India and East China. The inferred methane emissions by GOSAT observations are 7.7 Tg a−1 higher than those by TROPOMI observations over northern India but 7.0 Tg a−1 lower over East China. We find that the lower methane emissions from East China inferred by the GOSAT inversion are more consistent with independent ground-based in situ and total column (TCCON) observations, indicating that the TROPOMI retrievals may have high XCH4 biases in this region. We also evaluate inversion results against tropospheric aircraft observations over India during 2012–2014 by using a consistent GOSAT inversion of earlier years as an inter-comparison platform. This indirect evaluation favors lower methane emissions from northern India inferred by the TROPOMI inversion. We find that in this case the discrepancy in emission inference is contributed by differences in data coverage (highly uneven observations by GOSAT vs. good spatial coverage by TROPOMI) over northern India.