Dataset Information

US COVID-19 Shutdown Demonstrates Importance of Background NO₂ in Inferring NO_x Emissions From Satellite NO₂ Observations.

ABSTRACT: Satellite nitrogen dioxide (NO₂) measurements are used extensively to infer nitrogen oxide emissions and their trends, but interpretation can be complicated by background contributions to the NO₂ column sensed from space. We use the step decrease of US anthropogenic emissions from the COVID-19 shutdown to compare the responses of NO₂ concentrations observed at surface network sites and from satellites (Ozone Monitoring Instrument [OMI], Tropospheric Ozone Monitoring Instrument [TROPOMI]). After correcting for differences in meteorology, surface NO₂ measurements for 2020 show decreases of 20% in March-April and 10% in May-August compared to 2019. The satellites show much weaker responses in March-June and no decrease in July-August, consistent with a large background contribution to the NO₂ column. Inspection of the long-term OMI trend over remote US regions shows a rising summertime NO₂ background from 2010 to 2019 potentially attributable to wildfires.

SUBMITTER: Qu Z

PROVIDER: S-EPMC8206743 | biostudies-literature | 2021 May

REPOSITORIES: biostudies-literature

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US COVID-19 Shutdown Demonstrates Importance of Background NO2 in Inferring NOx Emissions From Satellite NO2 Observations.

Qu Zhen Z Jacob Daniel J DJ Silvern Rachel F RF Shah Viral V Campbell Patrick C PC Valin Lukas C LC Murray Lee T LT

Geophysical research letters 20210518 10

Satellite nitrogen dioxide (NO2) measurements are used extensively to infer nitrogen oxide emissions and their trends, but interpretation can be complicated by background contributions to the NO2 column sensed from space. We use the step decrease of US anthropogenic emissions from the COVID-19 shutdown to compare the responses of NO2 concentrations observed at surface network sites and from satellites (Ozone Monitoring Instrument [OMI], Tropospheric Ozone Monitor ...[more]

PMID: 34149109

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Project description:We employ new global space-based measurements of atmospheric methanol from the Tropospheric Emission Spectrometer (TES) with the adjoint of the GEOS-Chem chemical transport model to quantify terrestrial emissions of methanol to the atmosphere. Biogenic methanol emissions in the model are based on version 2.1 of the Model of Emissions of Gases and Aerosols from Nature (MEGANv2.1), using leaf area data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) and GEOS-5 assimilated meteorological fields. We first carry out a pseudo observation test to validate the overall approach, and find that the TES sampling density is sufficient to accurately quantify regional- to continental-scale methanol emissions using this method. A global inversion of two years of TES data yields an optimized annual global surface flux of 122 Tg yr-1 (including biogenic, pyrogenic, and anthropogenic sources), an increase of 60 % from the a priori global flux of 76 Tg yr-1. Global terrestrial methanol emissions are thus nearly 25 % those of isoprene (~540 Tg yr-1), and are comparable to the combined emissions of all anthropogenic volatile organic compounds (~100-200 Tg yr-1). Our a posteriori terrestrial methanol source leads to a strong improvement of the simulation relative to an ensemble of airborne observations, and corroborates two other recent top-down estimates (114-120 Tg yr-1) derived using in situ and space-based measurements. Inversions testing the sensitivity of optimized fluxes to model errors in OH, dry deposition, and oceanic uptake of methanol, as well as to the assumed a priori constraint, lead to global fluxes ranging from 118 to 126 Tg yr-1. The TES data imply a relatively modest revision of model emissions over most of the tropics, but a significant upward revision in midlatitudes, particularly over Europe and North America. We interpret the inversion results in terms of specific source types using the methanol : CO correlations measured by TES, and find that biogenic emissions are overestimated relative to biomass burning and anthropogenic emissions in central Africa and southeastern China, while they are underestimated in regions such as Brazil and the US. Based on our optimized emissions, methanol accounts for > 25 % of the photochemical source of CO and HCHO over many parts of the northern extratropics during springtime, and contributes ~6 % of the global secondary source of those compounds annually.

Dataset Information

US COVID-19 Shutdown Demonstrates Importance of Background NO₂ in Inferring NO_x Emissions From Satellite NO₂ Observations.

Publications

US COVID-19 Shutdown Demonstrates Importance of Background NO<sub>2</sub> in Inferring NO<sub>x</sub> Emissions From Satellite NO<sub>2</sub> Observations.

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