Policy-relevant applications of OMI NO2 and TROPOMI NO2 satellite data: Estimating NOX emissions and inferring CO2 emissions

To better estimate satellite-based NO₂ column densities in urban areas and in areas with power plants, we use regional chemical transport models to re-calculate tropospheric air mass factors and tropospheric NO₂ vertical columns for the OMI and TROPOMI NO₂ products in North America. For both satellite products, tropospheric columns increase by up to 50% in city centers, and decrease by ~20% in the rural areas outside of urban areas when compared to the operational products. The enhanced products show better agreement with the Pandora NO₂ and aircraft measurements acquired during NASA field campaigns, signifying that the enhanced products are a better indicator of surface concentrations and emissions than the operational products. We use these enhanced OMI NO₂ and TROPOMI NO₂ products to estimate NO_X emissions and infer CO₂ emissions. A statistical model is fit to an oversampling of rotated NO₂ plumes observed from OMI and TROPOMI, and is used to calculate top-down NO_X emissions. These top-down emissions are also compared to each other for the summer of 2018. We then apply city-specific NOx-to-CO₂ ratios from bottom-up emission inventories to the top-down NOx emissions to develop first-order approximations of CO₂ emissions from fossil-fuel combustion. For 2017, we report annual fossil-fuel CO₂ emissions to be: Los Angeles 113 ± 49 Tg/yr; New York City 144 ± 62 Tg/yr; and Chicago 55 ± 24 Tg/yr. A study in the Los Angeles area, using independent methods, reported a 2013 – 2016 average CO₂ emissions rate of 104 Tg/yr and 120 Tg/yr, which suggests that the emissions rates from our method are in good agreement with other studies’ top-down estimates. Future work will focus on using the simultaneous measurements from both instruments to build upon OMI’s legacy of providing policy-relevant information to regulators assessing the effectiveness of air pollution reduction strategies.