Indirect Chemical Formation Dominates India's PM2.5 Pollution

A CREA analysis reveals that up to 42% of India’s PM2.5 pollution is secondary particulate matter, chemically formed from precursor gases like sulphur dioxide, nitrogen oxides, and ammonia. India is the world's largest SO2 emitter, primarily from coal power plants. This pollution is a widespread, year-round crisis across all states, with Delhi being the most polluted. Critically, current air quality strategies overlook these chemically formed particles, focusing instead on visible sources. Effective improvement requires addressing precursor gas emissions.

A comprehensive analysis by the Centre for Research on Energy and Clean Air (CREA) highlights that a substantial portion, up to 42%, of India's PM2.5 pollution is not directly emitted but is chemically formed in the atmosphere. This secondary particulate matter, predominantly ammonium sulphate, originates from precursor gases such as sulphur dioxide (SO2), nitrogen oxides (NOx), and ammonia (NH3). India is the global leader in SO2 emissions, largely due to coal-fired power plants contributing over 60% of national SO2 output. The report underscores that this harmful PM2.5 concentration is a widespread, year-round crisis affecting all 33 states and union territories, with 28 exceeding India’s National Ambient Air Quality Standard and all breaching WHO guidelines. Delhi registers as the most polluted, with annual mean PM2.5 levels twenty times the WHO guidelines. Regional disparities are stark, with the Indo-Gangetic airshed remaining consistently polluted and the Northeast emerging as a concern. Ammonium sulphate constitutes a significant portion of PM2.5 across states, peaking in winter and post-monsoon periods. For instance, Chhattisgarh recorded the highest annual ammonium sulphate contribution at 42%. A critical finding is that current air quality strategies are inadequate, prioritizing visible sources like road dust and PM10, while largely neglecting the crucial role of precursor gases. Achieving sustainable air quality improvements necessitates a decisive shift in focus to control these indirect emission sources.