Study of PM2.5 from 1998 to 2022 recommends 15 zones across country to better handle pollution

Categorising India into 15 distinct geographical zones or “airsheds,” each with its own unique climate and pollution sources, can significantly enhance the precision of efforts to combat air pollution particularly in sensitive areas such as the “Trans Gangetic Plains” which has Delhi at its centre, according to a new study.
The study, published in the Multidisciplinary Digital Publishing Institute (MDPI)’s air journal, analysed PM2.5 (particulate matter having a diameter of 2.5 microns or less) data between 1998 and 2022, and assessed the India Meteorological Department’s (IMD’s) climatological airsheds and long-term emissions inventory.
It identifies urban centres within each airshed, generally major cities or state capitals, where targeted actions would be required.
“Although attention often centres on stubble burning in Punjab and Haryana as the primary source of Delhi’s pollution, a broader, regional approach is essential for truly tackling the issue which looks at the problem from a multisector and socioeconomic perspective than focus on a source. How can Delhi and its neighbouring areas work together to address all the major sources that contribute to the problem: residential, industrial, transport and waste combustion sources?” said Sarath Guttikunda, the study’s author and founder-director of the air pollution think tank Urban Emissions Info.
The peer-reviewed study “Designating Airsheds in India for Urban and Regional Air Quality Management” defined airsheds as areas where pollution must be managed holistically, cutting across state boundaries, thus necessitatig state-specific air pollution management plans and improved interstate coordination. “Not only will it benefit Delhi, but the entire Indo-Gangetic plain and the country as a whole,” Guttikunda said.
Anumita Roychowdhury, executive director, research and advocacy at the Centre for Science and Environment (CSE) said identifying airsheds was the easy part, but executing airshed-specific plans was where NCR is still lacking.
“We have seen it with NCR, where the Commission for Air Quality Management (CAQM) has the mandate to enforce rules for the region. However, even then, we see lack of cooperation between states and limited action. It will be difficult to enforce this across the country, unless we see the will between states and local bodies to take action,” she said.
The divisions
The study said there is a need to divide India into airsheds due to high pollution, not just in Delhi-NCR but also in the country’s 131 non-attainment cities—those not meeting the prescribed PM2.5 and PM10 standards.
India’s 15 airsheds are grouped into six physical land blocks: the Himalayan region (two airsheds), the Indo-Gangetic Plains (four airsheds), the Plateau region (four airsheds), the Arid or Desert region (one airshed), the Coastal Plains (three airsheds), and the Islands (one airshed). For instance, the Western Himalayas airshed, centred in Dehradun, spans Ladakh, Himachal Pradesh, and Jammu and Kashmir, while the East Himalayas airshed, centred in Guwahati, covers northeast India.
Delhi is at the centre of the Trans-Gangetic Plain airshed, which includes Punjab, Haryana, and the National Capital Region.
Kanpur is at the centre of the Upper Gangetic Plain airshed, Patna at the centre of the Middle Gangetic Plain, Kolkata at the centre of Lower Gangetic Plain, Indore at centre of Central Plateau, Nagpur at centre of Western Plateau, Raipur at centre of Eastern Plateau, Bengaluru at centre of Southern Plateau, Mumbai the centre of West Coast and Chennai at centre of East Coast airshed.
“The largest block is the plateaus, covering 40% of the landmass and hosting 36% of the population. Within the blocks, airsheds share approximate equal sizes,” the study said.
Localised solutions needed
Discussing Delhi-NCR being classified as a priority, Guttikunda said: “The Indo-Gangetic Plain bears a heavy pollution burden, and even cities like Delhi… can benefit from a regional airshed strategy. For the NCR, this would involve collaboration among ULBs, state bodies, and ministries of the designated airshed beyond the city boundaries, to address shared air quality concerns, ensuring that coordinated action improves outcomes for all.”
The study also highlighted significant pollution increases in other areas. The Western Plateau airshed recorded the highest rise in PM2.5 concentrations, with levels climbing by 87% from 21.4µg/m³ in 1998 to 40µg/m³ in 2022. The West Coast airshed saw an 83% increase over the same period, rising from 13µg/m³ to 23.7µg/m³.
While initial calculations were aligned with administrative boundaries for governance — for governance purposes — Guttikunda says the eventual emissions and pollution modelling will require the need to set airsheds beyond physical boundaries.
Guttikunda said while the focus remains on Delhi-NCR, most cities in the country are not meeting the ambient air quality standards, including coastal cities, such as Mumbai.
“While regions like the Indo-Gangetic Plain bear the brunt of industrial and agricultural pollution, contrary to popular belief, coastal cities like Mumbai have also witnessed a spike in pollution. The airsheds all aim to capture different localised problems, based on the local climate,” he said.
The study does not quantify potential pollution reductions by airshed, noting that outcomes will depend on the unique challenges and conditions of each region.