What is secondary particulate matter in Delhi's air?

Secondary particulate matter forms in the atmosphere when precursor gases like sulphur dioxide and ammonia react.

Why aren't Delhi's current pollution controls working as well?

Current plans target directly emitted pollution; they struggle with invisible, atmospherically formed secondary pollutants.

What can Delhi learn from cities like London or Los Angeles about pollution?

These cities faced similar challenges with secondary pollution, requiring broader coordination and sustained effort on precursor gases.

Home / Environment / Delhi's Pollution: Beyond Visible Smog to Invisible Chemistry

Delhi's Pollution: Beyond Visible Smog to Invisible Chemistry

20 Jan

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Summary

Secondary particulate matter forms in the atmosphere from precursor gases.
Ammonium sulphate and nitrate near a third of Delhi's PM2.5.
Past successes in Los Angeles, London, Beijing show similar pollution challenges.

Delhi's Pollution: Beyond Visible Smog to Invisible Chemistry

The battle against severe pollution days in Delhi is entering a more complex phase, moving beyond visible, directly emitted pollutants to those formed invisibly in the atmosphere. Early successes in controlling PM10 and PM2.5 through measures like public transport conversion to CNG and tighter fuel standards have plateaued.

Scientists now understand that a substantial share of PM2.5 is secondary particulate matter, created when gases like sulphur dioxide, nitrogen oxides, and ammonia react. Studies indicate these secondary inorganic aerosols account for close to a third of Delhi's annual PM2.5, a figure that rises significantly during winter smog.

This invisible pollution poses a challenge for public perception and existing action plans, which were designed for primary emitters. Addressing it requires a non-linear approach, targeting precursor gases through broader, earlier, and more intensive policy interventions.