Delhi's winter pollution crisis is more complicated than smoke from vehicles, factories and burning waste. A significant share of the tiny particles that make the capital's air unhealthy forms through chemical reactions after gases enter the atmosphere. A government analysis found that secondary particulate matter accounted for 27% of Delhi's winter PM2.5 pollution, making it the largest individual category in the study. Now, a newly inaugurated atmospheric-chemistry laboratory promises a closer look at what people are breathing, although its preliminary findings have already raised questions about accuracy and the origins of pollutants.

The Integrated Atmospheric Chemistry and Aerosol Toxicity Analysis Laboratory (AATAL) was inaugurated on October 24, 2026, at the Indian Institute of Tropical Meteorology's (IITM) Delhi branch in New Rajendra Nagar.

Delhi Air Pollution: What the Winter PM2.5 Numbers Reveal

A meta-analysis covering source-apportionment studies conducted between 2015 and 2025 identified secondary particles as the leading category contributing to the capital's winter PM2.5 burden.

The findings were reviewed by the Commission for Air Quality Management (CAQM) and announced in a Press Information Bureau release dated February 20, 2026.

The remaining share covers other contributions not itemised in the government's summary. These figures describe findings drawn from earlier studies, rather than a live breakdown for October 2026.Secondary particles form when gases such as nitrogen oxides, sulphur dioxide, ammonia and volatile organic compounds react in the atmosphere. Vehicles, industries, agricultural activities and burning fuels can all release substances involved in these reactions.

This makes Delhi air pollution difficult to control through action against visible smoke alone. Emissions released in one location can contribute to particle formation elsewhere.

New IITM Laboratory Finds a Changing Pollution Mix

The AATAL facility, inaugurated by Union Minister Jitendra Singh, is designed to examine the chemical composition, potential toxicity and sources of fine particulate pollution.

According to the Ministry of Earth Sciences, the laboratory combines advanced chemical-analysis instruments with forecasting and source-apportionment systems. Early measurements reported by The Times of India on October 25 showed the following estimates for Saturday:

The two secondary-aerosol categories together accounted for 34.9% in that snapshot. Project director Sachin Ghude also suggested that approximately 40% of Delhi's PM2.5 was directly emitted, while roughly 60% formed through atmospheric reactions. However, the 60% estimate, the laboratory's daily percentages and CAQM's historical 27% figure should not be treated as interchangeable. They reflect different assessments, timeframes and classifications.

Why the New Pollution Data Still Has Limitations

The laboratory represents a significant improvement in Delhi's monitoring capabilities, but its early readings require caution. A Hindustan Times investigation published on October 25 found that the system had not yet established where some secondary particles originated. It also reported differences between the laboratory's PM2.5 measurements and readings from Delhi's wider monitoring network.

For October 22, the new system reported 55.3 micrograms per cubic metre, compared with a median of 117.1 across 37 Central Pollution Control Board monitoring stations. Measurements from different sites and methods are not automatically equivalent. Nevertheless, the discrepancy raises questions that researchers must address before the data can consistently guide major policy decisions. Officials acknowledged that the laboratory was experiencing initial technical difficulties. Some preliminary readings were also revised.

A New 500-Metre Emissions Map Is Being Developed

The CAQM has separately commissioned an updated emissions inventory covering Delhi and the National Capital Region. The project, announced in January 2026, uses a 500-metre-by-500-metre grid and 2026 as its base year. A consortium led by the Automotive Research Association of India, with IIT Delhi, TERI and IITM Pune, is preparing the study.

According to Hindustan Times, the exercise aims to provide updated emissions information for more accurate pollution forecasting and targeted interventions. The completed inventory is expected by June 2027, meaning it is not yet available for the current winter. Separately, the government's AIRWISE forecasting system is designed to provide 72-hour air-quality predictions at a spatial resolution of 400 metres. This is a forecasting capability, not the same as the new emissions inventory.

What This Means for Delhi's Winter Pollution Fight

The challenge is no longer simply identifying which activities produce visible smoke. Authorities must also understand which gases contribute to secondary aerosols and how pollution moves across Delhi-NCR. Reducing emissions from transport, industry, waste burning and agricultural activities remains essential because these sectors can produce both direct particles and the gases that form secondary pollution.

The CAQM has already activated Stage I of the Graded Response Action Plan after Delhi's daily AQI reached 245 on October 21. The new laboratory could eventually help agencies decide which pollution sources require the most urgent attention on a particular day. But the effectiveness of that approach will depend on reliable measurements, clearer identification of secondary-particle origins and a completed emissions inventory. For Delhi air pollution, the latest developments mark progress in understanding the problem, not proof that the city's winter smog is finally under control.