Seasonal dynamics and trends in air pollutants: A comprehensive analysis of PM2.5, NO2, CO, SO2 and O3 in Houston, USA

Abstract

Understanding the seasonal dynamics and long-term trends of air pollutants is crucial for effective air quality management. This study investigates the concentrations, trends, and spatial variations of five key pollutants—PM_2.5, NO₂, CO, SO₂, and O₃—in Houston, USA, over a seven-year period (2018–2024) using ground-based and satellite observations. The results indicate a significant rise in PM_2.5 and NO₂ concentrations, with annual averages increasing by 23% and 7.3%, respectively, highlighting the impact of industrial emissions and vehicular traffic. In contrast, SO₂ levels declined by 44%, reflecting the effectiveness of regulatory measures. Seasonal variations reveal that PM_2.5 peaks in summer due to secondary formation processes enhanced by photochemical activity, as evidenced by a concurrent rise in O₃ levels. In contrast, NO₂, CO, and SO₂ concentrations are highest in winter, influenced by atmospheric stability and heating-related emissions. Meteorological analysis revealed temperature, relative humidity and wind speed as key drivers of pollutant variability. Source apportionment via Positive Matrix Factorization (PMF) analysis identified three major contributors: vehicle emissions (55.2%), secondary aerosol precursors (35.3%), and industrial combustion (9.5%). Spatial analysis identifies key pollution hotspots near industrial corridors and high-traffic zones, emphasizing the need for targeted mitigation strategies. This study underscores the necessity of integrating continuous monitoring with policy interventions to address rising pollution levels and safeguard public health in rapidly urbanizing regions.