NO _x and HCHO in Hot Extremes Observed From Space and Their Influences on Urban Populations: A Case Study in Houston, TX (USA)

Abstract

Hot extremes have increased globally and on a regional scale. Traditional data processing methods to understand air quality changes in hot extremes may not adequately describe variations in directly emitted air pollutants like nitrogen oxides (NO _x ) or volatile organic compounds (VOCs) and their influence on secondary species such as ozone (O ₃ ). In Houston, TX (USA), the TROPOspheric Monitoring Instrument (TROPOMI) NO ₂ and HCHO columns observed an increase of 4.92% and 21.25%, respectively, in hot extremes, but the increase and resulting vulnerability on populations were not uniform spatially and temporally, which can go unrecognized. A clustering algorithm CLASP (CLustering of Atmospheric Satellite Products) was applied to capture variations and describe high magnitude features in TROPOMI observations on their spatial, magnitude, and temporal axes. CLASP qualified variations of NO ₂ and HCHO in hot extremes driven by biogenic and anthropogenic variables, by identifying increases in the magnitude and frequency of high magnitude hotspots in Houston. Population‐weighted TROPOMI columns together with CLASP inform how communities of color observe higher weighted population columns and experience a higher frequency and magnitude of NO ₂ and HCHO columns intensifying in hot extremes. Taking an observational approach to describe ozone air quality, we show how CLASP can help inform of variation captured in the TROPOMI column and identify limitations, highlighting the need to clarify how hot extremes affect ozone air quality in regions which may face exacerbated extremes.