Spatio-Temporal and Seasonal Variation of Ambient Air Pollutants and their Relation to Meteorological Factors in Ajmer and Alwar of Rajasthan during 2018-2023

Urban air quality is deteriorating with increased pollutant concentrations due to anthropogenic activities. Meteorological conditions further influence spatial and seasonal distribution of these pollutants. This study investigated spatial and seasonal variations of Particulate Matter (PM2.5 and PM10), Nitrogen Dioxide (NO2), Sulfur Dioxide (SO2), and Ozone (O3), and their relationships with meteorological parameters from 2018-2023 at Ajmer and Alwar monitoring stations. Monthly and annual mean concentrations of all pollutants, except O3, peaked during winter, followed by pre-monsoon, post-monsoon, and lower during monsoon across both cities, attributed to rapid industrialization and urbanization. In Ajmer and Alwar, highest mean concentrations of PM2.5 (55.71 and 31.2μg/m³), PM10 (210 and 178μg/m³), NO2 (52 and 45μg/m³), SO2 (69.20 and 20.49μg/m³), and O3 (46.94 and 49.93μg/m³) exceeded National Ambient Air Quality Standards (NAAQS) by 2.2-4.2 times, indicating severe air pollution. NO2 and SO2 concentrations positive correlated with temperature (T) (r = 0.52-0.68) and negative correlated with relative humidity (RH) (r = –0.40 to –0.55), whereas O3 strong positive correlated with T (r = 0.61), reflecting photochemical formation under high solar radiation. Regression analysis indicated that Wind Speed (WS) and Direction (WD) explained 60% of pollutant variability (R² = 0.61-0.72), being the strongest influences on pollutant concentrations as compared to T and RH. Overall, Ajmer recorded higher pollution levels due to dense traffic, and construction activity, while Alwar showed strong meteorological variation. The findings emphasize the need for regionspecific and season-adaptive mitigation strategies, and highlight implications for public and occupational health protection in semi-arid urban environments. Implementation of precautionary measures is essential to minimize public exposure to pollutants and reduce emissions at the source. This investigation further suggests the need for comprehensive studies on adverse impacts of air pollution on human health using appropriate environmental risk assessment techniques, which can support evidence-based air quality management at the regional scale. Major Findings: Study found PM2.5, PM10, NO2, and SO2 levels in Ajmer and Alwar consistently exceeded NAAQS limits, peaking during winter and pre-monsoon due to emissions and unfavorable meteorological conditions, while O3 levels were highest in summer from photochemical formation. Overall, findings emphasize the need for season-specific, site-based mitigation and occupational health measures to manage pollution in semi-arid urban regions.