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. Tropospheric NO2 and ozone simulations have large uncertainties,but their biases, seasonality, and trends can be improved with NO2assimilations. We perform global top-down estimates of monthly NOxemissions using two Ozone Monitoring Instrument (OMI) NO2 retrievals (NASAv3 and DOMINOv2) from 2005to 2016 through a hybrid 4D-Var/mass balance inversion. Discrepancy inNO2 retrieval products is a major source of uncertainties in thetop-down NOx emission estimates. The different vertical sensitivitiesin the two NO2 retrievals affect both magnitude and seasonal variationsof top-down NOx emissions. The 12-year averages of regional NOxbudgets from the NASA posterior emissions are 37 % to 53 % smaller thanthe DOMINO posterior emissions. Consequently, the DOMINO posterior surface NO2simulations greatly reduced the negative biases in China (by 15 %) and theUS (by 22 %) compared to surface NO2 measurements. Posterior NOxemissions show consistent trends over China, the US, India, and Mexicoconstrained by the two retrievals. Emission trends are less robust overSouth America, Australia, western Europe, and Africa, where the tworetrievals show less consistency. NO2 trends have more consistentdecreases (by 26 %) with the measurements (by 32 %) in the US from 2006to 2016 when using the NASA posterior emissions. The performance of posterior ozonesimulations has spatial heterogeneities from region to region. On a globalscale, ozone simulations using NASA-based emissions alleviate the doublepeak in the prior simulation of global ozone seasonality. The higherabundances of NO2 from the DOMINO posterior simulations increase the globalbackground ozone concentrations and therefore reduce the negative biasesmore than the NASA posterior simulations using GEOS-Chem v12 at remotesites. Compared to surface ozone measurements, posterior simulations havemore consistent magnitude and interannual variations than the priorestimates, but the performance from the NASA-based and DOMINO-basedemissions varies across ozone metrics. The limited availability of remote-sensing data and the use of prior NOx diurnal variations hinderimprovement of ozone diurnal variations from the assimilation, and thereforehave mixed performance on improving different ozone metrics. Additionalimprovements in posterior NO2 and ozone simulations require moreprecise and consistent NO2 retrieval products, more accurate diurnalvariations of NOx and VOC emissions, and improved simulations of ozonechemistry and depositions.

atmospheric chemistry and physics

Impacts of global NO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; inversions on NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and ozone simulations