What happened
IITM's newly inaugurated Aatal lab apportioned Delhi PM2.5 between October 20 and 24 and put secondary, in-atmosphere aerosols at 29.3 to 42.2% of the daily load.
Why it matters
For residents of Delhi, 'poor' air continues into winter with the biggest chunk of particulate mass still unattributable, and the forecast model used to warn the city is running on data nearly a decade old.
Remember this
More than a quarter of Delhi PM2.5 comes from sources IITM still cannot point to.
More context & who is affected
Delhi's air sat in the CPCB 'poor' band this week, and a new IITM lab in Pune has started apportioning where that PM2.5 actually comes from. Its own scientists admit the picture is only half-solved.
The Aatal source study, read from October 20 to 24, puts secondary sources — gases converting into particles in the air — at 29.3 to 42.2% of daily PM2.5. Vehicles come in second at 19.4 to 27.6%, well behind the reactive mass IITM still cannot trace back to an original emitter.
Compounding the gap, the DSS forecast model IITM uses for Delhi still runs on a 2021 emissions inventory built from 2016 surveys, with a replacement only promised by June 2027.
- Secondary sources share of PM2.5
- 29.3 to 42.2% IITM Aatal lab estimate for Oct 20-24, ahead of vehicles at 19.4-27.6%.Hindustan Times
- DSS emissions inventory age
- 2021 (from 2016 surveys) Replacement due only by June 2027; no nitrate or SOA chemistry simulated.Hindustan Times
- Aatal lab cost and scope
- Rs 80 crore, 25 instruments IITM Aatal lab at New Rajendra Nagar, Pune, inaugurated Oct 24 by Union MoS Jitendra Singh.Hindustan Times
Timeline
- Oct 20-24 — IITM Aatal lab records 29.3 to 42.2% secondary PM2.5.
- Oct 24 — Union MoS Jitendra Singh inaugurates the Rs 80 crore Aatal lab in Pune.
- June 2027 — Deadline for replacing IITM's 2021 emissions inventory.
General Public
Delhi residents kept breathing 'poor' air across the week, with the biggest chunk of particulate mass still unattributable.
Environment Watchers
With 29.3 to 42.2% of PM2.5 coming from unattributed secondary sources, IITM cannot point regulators at a single emitter to target.
Urban Health Readers
The DSS forecast model used for Delhi alerts still runs on a 2021 emissions inventory drawn from 2016 surveys, with a replacement due only by June 2027.
Reporting fromHindustan Times ↗NDTV ↗
Sources & verification2 sources · 4 claims
These are the records behind this briefing. Linked reporting is not the same as independent confirmation.
- Hindustan TimesReporting
Delhi gets pollution source data, but a big chunk stays unexplained ↗
Published Oct 25, 2026 · Accessed Oct 25, 2026 - NDTVReporting
Mumbai Air 'Very Poor' At 322 As Delhi Records Best October 24 In A Decade ↗
Published Oct 24, 2026 · Accessed Oct 25, 2026
Claims and linked sources
IITM's Aatal lab puts secondary sources at 29.3 to 42.2% of daily PM2.5 between October 20 and 24, ahead of vehicles at 19.4 to 27.6%.
IITM does not yet have a system to attribute those reactive secondary aerosols to an original emitting source.
The DSS forecast model IITM uses for Delhi still runs on a 2021 emissions inventory built from 2016 surveys, with a replacement only promised by June 2027.
Union MoS Jitendra Singh inaugurated the Rs 80 crore Aatal lab at New Rajendra Nagar, Pune on October 24, giving Delhi its first pollution source breakdown in about three years.
