The Influence of Anthropogenic NOx Emissions Observed from Space on Urban Populations and Ozone: A Case Study in Houston, TX (USA)

Hot extremes are virtually certain to increase due to a changing climate, but their short temporal time frame makes it difficult to observe their effects. Thus, how the air quality responds in hot extremes is less understood. We take an integrated approach employing TROPOMI and in situ observations, and GEOS-CF results to determine the effects of high-temperature extremes on NO_x and O₃ in Houston, TX, USA. We move beyond traditional spatial-temporal averaging and use an agile clustering algorithm, Clustering of Atmospheric Products (CLASP), to show the spatial and temporal variations of tropospheric column NO₂ in periods of non- and high temperatures. For the first time, we show CLASP’s application for capturing spatiotemporal changes of NO₂ columns in high-temperature periods and how satellite observations can capture NO₂ emissions from peak electricity-generating units (EGUs) and other major emission points. NO₂ columns are increased and are unequally distributed in hot extremes on a census tract level. With CLASP, population-weighted NO₂ column differences in hot extremes can range from 10% to 75%, where certain populations experience greater magnitude and frequency of NO₂ columns. The unequal distribution of NO_x emissions across the region leads to inhomogeneities in ozone formation and the ozone-temperature relationship at high-temperature extremes. Our results illustrate the importance of anthropogenic NO_x emissions in urban areas and the necessity to untangle the ozone-temperature relationship in hot extremes, so mitigation techniques can be enacted to help relieve the combined stress of high heat and poor air quality on our urban dwelling populations.