India’s peak air pollution puzzle: untangling the role of meteorology, emissions, and cross-border contribution

Understanding the interplay of emissions, meteorology, transboundary transport and chemistry is essential to explain India’s persistent air pollution, particularly during the post-monsoon and early winter months when particulate matter (PM 2.5 ) levels peak across the country. This study quantifies the relative contributions of these drivers to population-weighted nationally averaged PM 2.5 concentrations and their variability from 2017 to 2021 in the months from October to December by integrating top–down emissions from the GAINS-ASIA model with multi-year simulations using Weather Research and Forecasting–Community Multiscale Air Quality modelling framework. Sensitivity experiments isolating emissions, meteorology, and boundary conditions show that meteorological variability alone can alter population-weighted PM 2.5 levels between ±27 µ g m −3 (≈24%–36%), primarily through changes in boundary-layer height, wind speed, and ventilation coefficient. Transboundary inflows contribute between ±11 µ g m −3 (≈2%–14%), while emissions define the mean concentration but not its interannual variability. Despite a ∼10% rise in national PM 2.5 emissions between 2017 and 2021, observed and simulated concentrations declined over much of India, with mean PM₂.₅ across the Indo-Gangetic Plain falling from 159 µ g m −3 in 2017–103 µ g m −3 in 2021. These divergent trends underscore the strong meteorological control on air quality, as improved dispersion and reduced stagnation offset emission growth in several years. The results highlight that India’s air pollution problem is not emission-driven alone but dynamically modulated by meteorology and transport. Achieving sustained improvements, therefore, requires an integrated, airshed-based management approach that couples emission mitigation with dynamic meteorological forecasting and regional coordination across India.