India, Dec. 26 -- Nearly one-third of Delhi's annual PM2.5 pollution consists of secondary ammonium sulfate, according to a recent analysis by the Centre for Research on Energy and Clean Air (CREA). Health researchers warn that this component of air pollution may be more harmful than overall PM2.5 levels, with strong links to asthma and acute cardiac events.

A 2025 Harvard-led study, conducted by researchers from Harvard TH Chan School of Public Health, found that sulfate particles, including ammonium sulfate, were among the strongest contributors to asthma hospitalisations. The study reported a 10.6% increase in asthma hospital admissions among children for every decile increase in the sulfate-heavy pollution mixture. Researchers noted ...