Statistical Analysis of Diurnal, Seasonal, and Annual Variations of Criteria Air Pollutants for the San Antonio Metropolitan Area
A significant proportion of the population in San Antonio Metropolitan area is exposed to air pollutants that have concentrations above the standard values recommended by Environmental Protection Agency (EPA). In this work, air quality in the city of San Antonio is analyzed from the air quality data collected from 14 air quality monitoring sites located in this city during the timeframe of 2011 to 2020. The data have been used to investigate the diurnal and seasonal (monthly) variation of criteria pollutants, such as oxides of nitrogen, ground-level ozone, sulfur dioxide, particulate matter with aerodynamic diameter less than or equal to 2.5 µm, hydrogen sulfide, and carbon monoxide. The trends of annual pollutant concentrations have been explored to evaluate the significance of their long-term pattern. San Antonio is facing serious air quality problems, with O3 and PM2.5 concentrations regularly exceeding NAAQS in recent years. An objective of this study was to find out whether, and the extent to which, concentrations of air pollutants have changed over the observation period in relation to urbanization and community development. Apparent diurnal and seasonal behaviors were observed for NO, NO2, NOx, O3, PM2.5, SO2 at every San Antonio monitoring site reflecting the effect of variables like rush hour vehicle emission, temperature, solar radiation, indoor space heating, and meteorological conditions. An indexed annual mean concentration trend analysis for these criteria pollutants showed a steadily downward trend for NO, NO2, NOx (1%,11%, and 12% respectively) while O3 and PM2.5 showed a slight upward trend, rising to almost 6% and 7% respectively in San Antonio. A drop of 84% was observed in SO2 annual mean concentration trend while H2S almost doubled during the observation period.