Delhi PM2.5 Sources: How to Read the Evidence
Delhi’s PM2.5 comes from several sources and from chemical reactions in the atmosphere. There is no single source ranking that accurately describes every season, monitoring location and pollution episode.
The main categories to understand
| Category | What the label can include | What to check in a study |
|---|---|---|
| Transport | Exhaust and, depending on the method, non-exhaust particles | Whether road-dust resuspension is counted separately |
| Industry and energy | Manufacturing, kilns and fuel combustion | Geographic boundary and fuel assumptions |
| Dust | Road, soil and construction particles | PM10 versus PM2.5; these are not interchangeable |
| Burning | Crop residue, waste, biomass and other combustion | Whether agricultural fires are separated from other burning |
| Cooking | Household and commercial sources | Fuel, cooking process and overlap with biomass categories |
| Secondary particles | Particles formed from gases in the atmosphere | Whether they are assigned to emitting sectors or left as a separate category |
Transport from outside Delhi is a geographic origin, not another mutually exclusive sector. Imported particles can themselves come from industry, fires or other sources. Adding “outside Delhi” to all sector percentages may double-count pollution.
Emissions are not the same as ambient contribution
An emissions inventory estimates what sources release. A source-apportionment study estimates how different sources contribute to the concentration in the air being assessed. Weather, chemical reactions and transport connect the two.
One approach analyses the chemical composition of collected particles and uses a receptor model. Another combines emissions and atmospheric modelling. Their uncertainties and category definitions differ.
The TERI–ARAI study published in 2018 used both receptor and dispersion approaches for 2016. It is a dated research reference, not a measurement of today’s source split. Reporting its publication year as if it were the sampling year would be misleading.
Before sharing a percentage, ask five questions
- Which pollutant: PM2.5, PM10 or something else?
- Which place: one station, Delhi or the wider NCR?
- Which period: one day, winter, summer or the whole year?
- Which method and categories were used?
- Is the value observed, modelled, forecast or a policy scenario?
A high crop-fire contribution on one autumn day does not establish the annual share. A construction contribution to PM10 does not establish the same share of PM2.5. Ranges assembled from unrelated studies are not a new, validated combined estimate.
What a household can usefully do
Use local readings to plan immediate activity and indoor measurements to assess your home. A particle monitor cannot identify the source simply from a spike. Record cooking, nearby work, windows and wind as context without treating a correlation as proof.
Explore the specific guides to construction dust, stubble burning and traffic pollution. For household action, start with PM2.5 reduction at home.
FAQ
Why are the percentages so different across sources?
Different studies, different years, different methodologies. The consolidated picture (ranges, not single numbers) is more honest than any single percentage.
Is the IIT-Kanpur 2015 study still valid?
Largely yes, with adjustments. The qualitative source ranking is similar in newer studies. Vehicle composition has shifted (BS6, EVs growing), brick kiln conversion is advancing, but the overall framework holds.
Why isn’t there a more recent definitive study?
A new comprehensive Delhi source apportionment study was commissioned in 2024 (the 6th since 2010) and is in progress. Updated results expected 2025–26.
Does adding more roads reduce vehicle pollution?
No, generally the opposite. More road capacity induces more travel demand. Reducing total vehicle-km is the lever that matters.
Why is biomass burning year-round, not just stubble season?
Stubble burning is a 6-week agricultural phenomenon. Residential heating, garbage burning, construction-site fires, and rural biomass cooking happen year-round and collectively contribute more than stubble across the calendar.