While efforts to mitigate the severity of the air pollution in the Delhi-NCR have been taken over the years consistently, of late there has been a steady increase in the number of good air days with a decline in the registered ‘poor’ to ‘very poor’, and ‘severe’ to ‘severe (+) category air days, according to Dr SD Attri, an expert on the subject.
Dr Attri, full-time Member-Technical of the Commission for Air Quality Management (CAQM) in NCR and adjoining areas, said that the City Action Plans for the time-bound implementation of pollution mitigation measures aimed at improving Air Quality Index (AQI) are available in the public domain, to ensure transparency and awareness.
Notably, last year, Delhi had 79 days with the AQI of 100 or below that is in ‘Good’ and ‘Satisfactory’ categories. The year 2025 also recorded the second lowest number of “Severe to Severe+” AQI days, which was were 8, since 2018.
Explaining the air quality and pollution in Delhi-NCR, Dr Attri said that “ambient air” is the outdoor air people breathe across residential areas, roads, markets, work places and others while the “Ambient Air Pollution” is the concentration of pollutants in air such as PM2.5, PM10, Ozone, Nitrogen Oxides, Sulphur Dioxide, and Carbon Monoxide, measured at a given place and time.
He said the ambient air can’t be assessed just at emission sources due to dispersion, atmospheric physical and chemical processes. Therefore, the monitoring stations must be better placed at strategic points considering land use categories.
Dr Attri shared that Delhi-NCR falls in the Indo-Gangetic Airshed, one of the complex geographical locations, having a basin- like land- locked structure, preventing dispersion of pollutants, especially in winters owing to unfavourable meteorological conditions.
He said that the CAQM, on the directions of Supreme Court. brought a report from AQI experts in January, identifying causes behind worsening AQI in Delhi- NCR. Based on most recent report submittedto the apex court on the predominant sources of pollution , the contribution of vehicular emissions was found to be 23 per cent in winters, and 19 per cent in summers.
Industry, including TPPs, contributed 9 per cent of the pollution in winters and 14 per cent in summer.
The impact of dust from road, soil, and Construction & Demolition waste was 15 per cent in winters, and 27 per cent in summer.
Biomass burning is also one of the key sources, accounting for 20 per cent in winter and 12 per cent in summers.
Secondary particulate, transforming from gaseous emissions via transport, industries, and biomass burning, contributed 27 per cent, and in the summer, it adds 17 per cent.
Other miscellaneous sources add up to 6 per cent of the pollution during winters, and 11 per cent in the summers.
Dr Attri also shared that ‘Emission Inventory’ (EI) is a comprehensive geo-spatial database that quantifies sources, and amount of emission discharge within an area over a time period, identifying “who is emitting and how much.” It estimates emissions from transport industry, residential, commercial, other activities and sources.
He said knowing EI is crucial for identifying major pollution sectors, locations, long-term trends, and further designing mitigation strategies.
The expert also said that “Source Apportionment” (SA) determines contribution of multiple sources adding to air pollution at a given location and time, using measurement-based techniques, including chemical analysis of samples paired with receptor models, and dispersion modelling approaches.
There have been efforts to identify pollution sources by institutions like Indian Institute of Tropical Meteorology (IITM), IIT Kanpur, The Energy and Research Institute (TERI) and others in the last two decades.
After assessing existing EI and SA studies for Delhi- NCR, and finding limitations, the CAQM formed a National Level Expert Committee chaired by Dr Attri and developed a ‘Framework’ for a new EI and SA in April 2025, and Central Pollution Control Board was asked to implement it.
Institutions like ARAI, Pune, IIT Deļhi, TERI and IITM have been tasked to develop a new EI and SA for Delhi- NCR with 2026 as base year, which is expected to provide more accurate assessment of emissions, which will be used in Air Quality Early Warning System (AQEWS), and the Decision Support System (DSS) developed by IITM, which provides AQI forecasts and source contribution analysis, enabling policy interventions and actions for mitigation.
For strengthening AQI monitoring infrastructure, he says that new grid-based spatial coverage norms need to be adopted, with better placed monitoring stations.
He shared that in near future with strengthening of CAAQMS network, total stations in Delhi-NCR will be more than 150, that are 90 at present.