Meteorological modulation of ground-level air quality in India based on in situ measurements

In India, air pollution has become a significant environmental and public health concern due to rapid urbanisation, industrial development, and intensive agricultural activities. This research provides a comprehensive analysis of the monthly and seasonal trends of key air pollutants (PM $_{10}^{}$ , PM $_{2.5}^{}$ , O $_3^{}$ , NO $_2^{}$ , and SO $_2^{}$ ) along with meteorological factors (i.e. planetary boundary layer height, relative humidity, temperature, precipitation, wind patterns, and surface pressure) from 2017 to 2024. The outcome of this study reveals a significant decline in PM concentrations at several monitoring sites across the IGP region, with Sen's slope values ranging from -0.893 to -0.097 and -1.320 to -0.169 $\mu \text{g}{\text{m}}^{-3}{\text{month}}^{-1}$ for PM $_{2.5}^{}$ and PM $_{10}^{}$ , respectively. However, increasing trends were observed in Punjab, likely due to localised emission sources, and region-specific factors influenced a few southern sites. Further, O $_3^{}$ exhibited an increasing trend (0.041 to 0.529 $\mu \text{g}{\text{m}}^{-3}{\text{month}}^{-1}$ ) in several regions, highlighting the role of aerosol inhibition and enhanced precursor concentrations in promoting ozone formation. Additionally, NO $_2^{}$ and SO $_2^{}$ exhibited heterogeneous trends, with notable decreases in some regions likely reflecting stricter emission regulations, while others remained relatively stable. These trends were further modulated by meteorological conditions, as reduced PBLH and wind speed over northern and eastern India, except Delhi, along with increased humidity and surface pressure, contributed to pollutant accumulation. Mumbai and Bangalore experienced higher PBLH, winds, and precipitation, aiding pollutant dispersion. Correlation analysis demonstrated a positive association of PM with NO $_2^{}$ and SO $_2^{}$ ( $r\approx 0.5\text{to}0.6$ ), while O $_3^{}$ showed an inverse association with PM ( $r\approx -0.2\text{to}-0.8$ ) due to the role of aerosol attenuation, photochemical interactions, and region-specific precursor chemistry in regulating surface ozone levels. This study provides valuable insights into the spatiotemporal trends of air pollution across India and emphasises the need for continuous monitoring and region-specific mitigation strategies.