What’s Delhi breathing? IITM’s new lab decodes air mix

IITM’s new Integrated Atmospheric Chemistry and Aerosol Toxicity Analysis Laboratory identified vehicles as Delhi’s largest PM2.5 contributor in its latest data. It also separated pollution into secondary aerosols, road dust and waste burning. This matters because agencies can target specific sources instead of treating all pollution as identical.

Vehicles contributed 25%. Secondary organic aerosols contributed 18.4%, while secondary inorganic aerosols added 16.5%. Road dust contributed 10.9%, and waste burning contributed 5%. Secondary aerosols form when gases react in the atmosphere and become particles.

The laboratory provides real-time source-apportionment data. Its findings show that Delhi’s pollution mix changes from day to day. On Friday, secondary organic aerosols led at 24.6%, while vehicles and secondary inorganic aerosols each contributed 20.7%. The data can help CAQM and other agencies prioritise controls and assess their results.

The laboratory’s latest source-apportionment results assigned different shares of Delhi’s PM2.5 pollution to major sources. Vehicles contributed 25%, the largest single share. Secondary organic aerosols contributed 18.4%, and secondary inorganic aerosols contributed 16.5%. Together, these secondary forms made up 34.9%.

Road dust contributed 10.9%, while waste burning contributed 5%. These figures show that pollution comes from both direct emissions and chemical changes occurring in the atmosphere. The article also reports that road dust remained significant at 5% to 10% during recent days.

The shares are not fixed. On Friday, secondary organic aerosols became the largest contributor at 24.6%. Vehicles and secondary inorganic aerosols each contributed 20.7%. The changing proportions are why continuous measurements matter for deciding which sources need attention at a particular time.

PM2.5 means fine particulate matter with an aerodynamic diameter of 2.5 micrometres or less. These particles are small enough to travel deep into the respiratory system. The article focuses on measuring their sources, composition and possible health impacts through IITM’s new laboratory.

Their danger is linked to their size and chemical makeup. In general, fine particles can reach the deepest parts of the lungs and trigger inflammation. Some may also affect the cardiovascular system. The laboratory will examine smaller constituents, including metallic elements and other potentially harmful components, rather than measuring concentration alone.

Delhi’s PM2.5 is a mixture of primary particles, secondary organic aerosols, secondary inorganic aerosols, metals and toxic elements. Sachin Ghude said roughly 40% is primary and 60% secondary. Understanding that mixture can help agencies identify pollution with potentially different health effects and design better responses.

Primary particulate matter enters the air directly from a source. Examples in the article include particles associated with vehicles, road dust and waste burning. Secondary aerosols are different: they are not released as finished particles, but develop after gases undergo chemical reactions in the atmosphere.

The article identifies two major secondary groups. Volatile organic compounds can become secondary organic aerosols. Sulphur dioxide, nitrogen oxides and ammonia can react to produce secondary inorganic aerosols, including sulphates and nitrates. These processes can change the pollution mix after emissions leave their original sources.

Initial findings from IITM’s laboratory indicate that about 40% of Delhi’s PM2.5 is primary and 60% is secondary. Ghude described primary particles, secondary organic aerosols and secondary inorganic aerosols as roughly 30% each, with the remaining 10% comprising metals, toxic elements and other components.

Secondary aerosols form through atmospheric chemistry. Gases released by vehicles, industries, solvents and vegetation do not always remain gases. Volatile organic compounds, or VOCs, can react in the air and form secondary organic aerosols. This creates particulate pollution away from the moment of original release.

Secondary inorganic aerosols form through reactions involving sulphur dioxide, nitrogen oxides and ammonia. These reactions produce sulphates and nitrates, which become particles. The article also identifies waste burning as a PM2.5 source, although it does not detail a separate chemical pathway for that source.

This mechanism explains why source shares change over time. On Friday, secondary organic aerosols contributed 24.6%, exceeding vehicles and secondary inorganic aerosols, each at 20.7%. IITM’s laboratory is designed to track pollutants, their sources and their atmospheric transformation in real time.

Source-apportionment data shows where Delhi’s PM2.5 is coming from and how large each contribution is. That gives agencies a more precise basis for action than a single overall pollution number. They can focus on vehicles, dust, waste burning or atmospheric aerosol formation according to current evidence.

For example, vehicles led the latest results at 25%. On Friday, secondary organic aerosols led at 24.6%, while vehicles and secondary inorganic aerosols each contributed 20.7%. A response based only on the latest vehicle figure could miss a changing role for chemically formed particles.

The laboratory restores real-time source-apportionment data after nearly three years. It is expected to support CAQM and other agencies in identifying major sources, prioritising interventions and assessing effectiveness. Measurement-based evidence can pinpoint sectors and locations and support coordinated action across Delhi-NCR.

AQI summarises air-quality conditions, but the article highlights why the mixture behind that number also matters. Different pollutants can have different health impacts. Knowing only the concentration does not reveal whether pollution includes metallic elements, toxic components or chemically formed particles.

IITM’s laboratory is equipped to identify pollutants, trace their sources, study atmospheric transformation and assess potential health impacts. Its measurements will examine smaller constituents, including metals and other potentially harmful components. This adds detail to the broad question of whether pollution is high or low.

Jitendra Singh said earlier discussions focused mainly on whether pollution was 100 or 200. The new facility is intended to show what that pollution contains and where it comes from. That evidence can help agencies choose more targeted actions and better judge health risks, although the article does not assign specific health effects to each measured component.