Airshed

Geography glossary

Also called: Airshed approach · Topic: Geographical Issues: Pollution, Urban Waste, Slums and Land Degradation · NCERT: Beyond NCERT

Meaning

An airshed is a region where the air is shared. Pollutants mix and move together across the whole region, because hills, plains and winds shape where the air goes, not State or city borders. The airshed approach means managing air quality for the whole region together, instead of letting each city or State act alone.

This matters because smoke made in one State often ends up as smog in another. For north India, this explains why city-by-city plans have not been enough. It is a common GS-III theme.

Explanation

How an airshed forms (cause → process → result)

  • Cause: the shape of the land traps the air.
  • The Indo-Gangetic plain is a landlocked basin. Air has few easy ways to escape it.

  • Air flows and mixes freely inside this basin, so the whole plain behaves like one big room of air.

  • Process: winter weather locks the air in place.

  • Temperature inversion (cold air sits near the ground under a layer of warmer air) stops air near the ground from rising.
  • Low mixing height (the layer of air in which pollution can spread upward becomes very shallow) squeezes pollutants close to the ground.

  • Calm winds mean the polluted air is not blown away.

  • Process: winds carry pollution across borders.

  • North-westerly winds carry crop smoke and firecracker smoke down the Indo-Gangetic plain.

  • Stubble burning (farmers set fire to leftover paddy straw) in Punjab, Haryana and western UP in October–November adds smoke that drifts towards Delhi.

  • Result: smog in places that did not create most of the smoke.

  • Delhi's winter smog (November–January) mixes local pollution (vehicles, dust, industry, waste burning) with smoke from outside.
  • PM2.5 (very fine particles that go deep into the lungs) is the key pollutant in Delhi. It forms and travels across the whole airshed.

Why administrative borders fail

  • Pollution crosses borders. Clean air cannot be secured by one agency or one State acting alone.
  • A State can clean up its own sources and still have dirty air, because its neighbours' smoke flows in.
  • Because PM2.5 travels so widely, a breach at one monitoring station cannot easily be blamed on one chimney or one site.
  • City-by-city planning: NCAP gives each of its 131 non-attainment cities its own action plan. The debate is whether air should be managed across a whole airshed or city by city.

Parts of the airshed approach

  • One regional body with power over the whole airshed. In India this is the Commission for Air Quality Management (CAQM). It was set up under Act No. 29 of 2021 and is deemed to have come into force on 13 April 2021.
  • Exclusive jurisdiction: on matters under the Act, no other body can claim power over CAQM's subjects.
  • Coverage drawn by air, not maps: CAQM covers the NCR plus "adjoining areas" of Haryana, Punjab, Rajasthan and Uttar Pradesh, but only so far as they affect NCR air quality. This is a five-unit airshed (Delhi plus four States).
  • Shared data: one set of verified data for all agencies, such as CAQM's PAVAN-I3C platform, removes disputes over whose numbers are right.
  • Common rules and action plans: GRAP (four stages by AQI: Poor, Very Poor, Severe and Severe+) applies across the region. CAQM must also implement NCAP and NAAQS there.
  • Regional outcome targets: success is measured by cleaner air across the whole region, not by how many tools are built.

Where it occurs

  • Indo-Gangetic plain (north India): the clearest Indian airshed. Most non-attainment cities lie here, because the basin is landlocked and has winter inversions and dust.
  • Delhi-NCR airshed: Delhi plus adjoining areas of Haryana, Punjab, Rajasthan and UP. It is governed by CAQM under the 2021 Act.
  • Source areas: Punjab, Haryana and western UP. Stubble burning here in October–November affects Delhi.
  • Policy push: in December 2025, the Parliamentary Standing Committee recommended planning and enforcement at the airshed level for Delhi-NCR.
  • World example: Beijing–Tianjin–Hebei (China). Beijing worked with neighbouring provinces and cities, including Tianjin and Hebei, through a regional coordination mechanism. UNEP reported that between 2013 and 2017, PM2.5 fell by 35% in Beijing and by 25% in the surrounding region.

Don't confuse with

  • Watershed: a land area that drains into one river, with fixed borders set by ridges. An airshed is set by moving air and weather (inversions, wind direction), so its reach changes with the season.
  • Non-attainment city: one city that failed NAAQS for PM10 or NO₂ for five years in a row (2011–15). It is the unit of NCAP's city-by-city plans. An airshed is a whole region covering many cities and States.
  • CAQM: CAQM is a statutory body, the regulator. The airshed is the idea behind it, the shared body of air that CAQM is meant to govern.
  • Ambient monitoring vs source monitoring: airshed planning is about ambient (surrounding) air, measured by CAAQMS. OCEMS measures what comes out of one industrial stack, which is the source.

Prelims Hooks

  • CAQM's airshed covers the NCR plus adjoining areas of Haryana, Punjab, Rajasthan and UP. Himachal Pradesh is not included.
  • CAQM was created by Act No. 29 of 2021. It is deemed in force from 13 April 2021, and an Ordinance came before the Act.
  • CAQM's jurisdiction is exclusive on matters under the Act, and covers adjoining areas only so far as they affect NCR air quality, not each whole State.
  • NCAP (January 2019) is city-based: 131 non-attainment cities, each with its own plan. CAQM (2021) is airshed-based, covering one region across several States.
  • Delhi's winter smog is trapped by temperature inversion, low mixing height and calm winds. North-westerly winds carry crop smoke down the Indo-Gangetic plain.
  • Beijing–Tianjin–Hebei is the world model of regional airshed control: PM2.5 fell 35% in Beijing and 25% in the surrounding region between 2013 and 2017.

Mains Points

  • Why north Indian air pollution is an airshed problem:
  • Geography: the landlocked Indo-Gangetic basin, winter temperature inversions and low mixing height trap pollutants.
  • Cross-border sources: stubble burning in Punjab, Haryana and western UP, carried by north-westerly winds.

  • PM2.5 forms and travels across the whole airshed, so one city cannot fix its air alone.

  • Policy response and its gaps:

  • CAQM gives one regulator exclusive power over a five-unit airshed. This is a model of a regional regulator that cuts across normal State borders.
  • But field action still depends on State Pollution Control Boards and municipal bodies that work under State governments.

  • NCAP's city-by-city plans do not fully match the airshed reality. The Standing Committee (December 2025) urged airshed-level planning and enforcement.

  • Way forward:

  • Set a measurable PM2.5 target for the whole region and have it checked by an outside body, as Beijing did with UNEP.
  • Use shared data platforms such as PAVAN-I3C as the base for joint planning.
  • Apply the airshed approach to other Indo-Gangetic cities as well, for cooperative federalism (the Centre and States working together) in clean-air governance.

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