Temporal trends in AQI and precursor pollutants: a long-term case study of Noida

This study analyses the long-term variations in air quality at Amity University, Noida, Uttar Pradesh, India, from May 2017 to December 2024, focusing on the monthly mean Air Quality Index (AQI) and its key precursors. The specific objectives of the study are to: (i) characterize temporal trends in AQI; (ii) identify dominant pollutant drivers influencing seasonal air quality; and (iii) evaluate the relative contributions of anthropogenic and meteorological factors to observed variations. The average AQI during the period was 217, with peaks in winter due to temperature inversions and increased emissions, and improvements during monsoon months due to wet deposition. The highest AQI (487) was recorded in November 2017, while the lowest (40) was observed in July 2024. A notable reduction in AQI occurred during the COVID-19 lockdown in 2020, highlighting the impact of reduced anthropogenic activities. Particulate matter (PM_2.5 and PM₁₀) emerged as the primary contributor to high AQI, frequently exceeding the National Ambient Air Quality Standards (NAAQS) during winter. Nitrogen dioxide (NO₂) peaked in June 2023 (192 µg m^-³), while ammonia (NH₃) exhibited episodic spikes, mainly due to agricultural activities. Ground-level ozone (O₃) levels fluctuated, indicating variations in precursor emissions and photochemical processes. Correlation analysis revealed a strong relationship between AQI and PM_2.5 (r = 0.9) as well as PM₁₀ (r = 1.0), emphasizing particulate pollution as the dominant driver of poor air quality. Unlike studies that focus primarily on PM_2.5 and PM₁₀, this research gives equal attention to secondary pollutants and their role in shaping AQI trends. Local meteorological conditions play a critical role, and the associated emission sources were also examined to provide a comprehensive understanding of pollutant variability. The findings conclude that PM remains the most influential factor governing air quality in the region, and sustained improvement will require targeted emission control strategies addressing both primary particle sources and secondary pollutant formation pathways.