Global distribution of methane emissions: a comparative inverse analysis of observations from the TROPOMI and GOSAT satellite instruments
<p>We evaluate the global atmospheric methane column retrievals from the new TROPOMI satellite instrument and apply them to a global inversion of methane sources for 2019 at 2<span class="inline-formula"><sup>∘</sup></span> <span class="inline-formula&...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/14159/2021/acp-21-14159-2021.pdf |
| Summary: | <p>We evaluate the global atmospheric methane column retrievals from the new TROPOMI satellite instrument and apply them to a global inversion of
methane sources for 2019 at 2<span class="inline-formula"><sup>∘</sup></span> <span class="inline-formula">×</span> 2.5<span class="inline-formula"><sup>∘</sup></span> horizontal resolution. We compare the results to an inversion using the sparser but
more mature GOSAT satellite retrievals and to a joint inversion using both TROPOMI and GOSAT. Validation of TROPOMI and GOSAT with TCCON
ground-based measurements of methane columns, after correcting for retrieval differences in prior vertical profiles and averaging kernels using the
GEOS-Chem chemical transport model, shows global biases of <span class="inline-formula">−</span>2.7 <span class="inline-formula">ppbv</span> for TROPOMI and <span class="inline-formula">−</span>1.0 <span class="inline-formula">ppbv</span> for GOSAT and regional biases of
6.7 <span class="inline-formula">ppbv</span> for TROPOMI and 2.9 <span class="inline-formula">ppbv</span> for GOSAT. Intercomparison of TROPOMI and GOSAT shows larger regional discrepancies exceeding
20 <span class="inline-formula">ppbv</span>, mostly over regions with low surface albedo in the shortwave infrared where the TROPOMI retrieval may be biased. Our inversion uses
an analytical solution to the Bayesian inference of methane sources, thus providing an explicit characterization of error statistics and information
content together with the solution. TROPOMI has <span class="inline-formula">∼</span> 100 times more observations than GOSAT, but error correlation on the
2<span class="inline-formula"><sup>∘</sup></span> <span class="inline-formula">×</span> 2.5<span class="inline-formula"><sup>∘</sup></span> scale of the inversion and large spatial inhomogeneity in the number of observations make it less useful than
GOSAT for quantifying emissions at that scale. Finer-scale regional inversions would take better advantage of the TROPOMI data density. The TROPOMI
and GOSAT inversions show consistent downward adjustments of global oil–gas emissions relative to a prior estimate based on national inventory
reports to the United Nations Framework Convention on Climate Change but consistent increases in the south-central US and in Venezuela. Global
emissions from livestock (the largest anthropogenic source) are adjusted upward by TROPOMI and GOSAT relative to the EDGAR v4.3.2 prior estimate. We
find large artifacts in the TROPOMI inversion over southeast China, where seasonal rice emissions are particularly high but in phase with extensive
cloudiness and where coal emissions may be misallocated. Future advances in the TROPOMI retrieval together with finer-scale inversions and improved
accounting of error correlations should enable improved exploitation of TROPOMI observations to quantify and attribute methane emissions on the
global scale.</p> |
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| ISSN: | 1680-7316 1680-7324 |