Indirect PM2.5 Emissions in India Predominantly Chemically Formed
A CREA analysis reveals up to 42% of India's PM2.5 pollution is secondary particulate matter, mainly ammonium sulphate chemically formed from precursor gases like SO2. India is the top global SO2 emitter, largely from coal-fired power plants. This widespread issue, not just urban or seasonal, impacts all states, with Delhi being the most polluted. Current strategies overlook these precursor gases, limiting air quality improvements if secondary particle formation isn't addressed.
A recent 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, primarily ammonium sulphate, results from precursor gases like sulphur dioxide (SO2), nitrogen oxides (NOx), and ammonia (NH3). India is the world's largest SO2 emitter, contributing 11.2 million tonnes, with coal-fired power plants accounting for at least 60% of national SO2 emissions.The CREA report underscores that India's PM2.5 crisis is widespread and year-round, extending beyond metropolitan areas. Satellite data shows extreme regional disparities, with all 33 states and union territories exceeding WHO guidelines, and 28 also breaching India’s National Ambient Air Quality Standard (NAAQS). Delhi consistently ranks as the most polluted, where approximately one-third of its annual PM2.5, rising to almost half in winter smog, is ammonium sulphate formed from coal-burning emissions.Seasonal analysis reveals ammonium sulphate dominates PM2.5 during Delhi's most polluted periods (post-monsoon and winter). Across India, ammonium sulphate contributes between 17% and 42% of PM2.5 mass, peaking in winter and post-monsoon. The Indo-Gangetic airshed remains the most polluted, while the Northeast is an emerging concern. The findings expose critical gaps in current air quality strategies, which often prioritize visible pollution sources like PM10 and road dust, neglecting the crucial role of precursor gases. Addressing these secondary particulate matter formations is vital for effective and lasting air quality improvements.
