India’s Air Pollution

How Airshed Management Could Tackle India’s Air Pollution Crisis

By Deepa Padmanaban

In 2019, air pollution in India caused the premature deaths of more than a million people. That same year, the government established the National Clean Air Programme (NCAP). Three years later, the NCAP is widely described as ineffective, and India continues to rank among the top five most polluted countries in the world. Now, scientists are looking to a different approach to tackling the country’s toxic air, one based on the recognition that pollution transcends national and state borders.

The NCAP was formulated to tackle air pollution in cities, specifically to reduce particulate matter (PM2.5) pollution by 20 percent-30 percent from 2017 levels by 2024. But the nature of air pollution means there are limitations to a policy that focuses on urban areas.

Why is PM2.5 so harmful?

PM2.5 refers to tiny inhalable particles – particulate matter – with a diameter of 2.5 micrometres.

These particles are a mixture of solid and aerosol chemicals, mostly produced by burning fuels such as petrol, diesel, oil or wood.

PM2.5 pollutants are much smaller than the diameter of a human hair. Because these particles are so small, they can penetrate the lungs deeply, causing harm to people’s health

“Air pollution is not restricted to geopolitical boundaries,” points out SN Tripathi, professor of civil engineering at the Indian Institute of Technology (IIT) Kanpur and a member of the NCAP steering committee. South Asia’s geography and weather patterns mean that pollutants can travel long distances: a 2020 study of 22 regions showed that 46 percent of air pollution (adjusted for population distribution) originates from another Indian state.

“Because of the transboundary dispersion of air pollution, smaller towns that don’t have as many polluting industries experience high levels of pollution that come from larger cities,” says Kalyani Tembhe, programme officer at the Centre for Science and Environment, a think-tank in New Delhi.

“Air pollution depends on meteorology, topography and land-use patterns,” Tripathi agrees.

Because of this, Indian states are looking at new ways to tackle the crisis, with many planning to adopt airshed management. The World Bank defines an airshed as a common geographic area where pollutants get trapped, creating similar air quality for everyone. “We can reorganise… natural processes that govern the air, and identify airsheds,” Tripathi says.

The concept is demonstrated by a 2019 study that found approximately half of the population-weighted PM2.5 in Delhi comes from outside the territory, of which 50 percent is from Haryana and Uttar Pradesh. In Punjab, about 60 percent of PM2.5 does not originate within the state, with about half coming from outside India and half from other Indian states. In Uttar Pradesh, only half of PM2.5 originates within the state.

Sagnik Dey, a professor at the Centre for Atmospheric Sciences at IIT Delhi, has identified the major regional airsheds that impact India, based on satellite data for PM2.5.

“The whole idea is that, within an airshed, the overall patterns of air quality from season to season are similar over the long term. There are nine to 11 airsheds in India. Some, like the Indo-Gangetic Plain airshed, within which lie two or more regional airsheds, are gigantic,” he says. The Indo-Gangetic Plain covers the states of Rajasthan, Punjab, Uttar Pradesh, Delhi, Haryana, Bihar and West Bengal, and extends to Nepal, Bangladesh and Pakistan.

How would airshed management work in India?

The idea of airsheds is not new. The Canadian province of British Columbia and California in the US have both used an airshed approach to tackle air pollution. The Air Quality Act of 1967 divided California into 35 districts with similar geographic, topographic and meteorological conditions, where pollution is regulated by the California Air Resources Board. By 2019, this approach had achieved a 98 percent reduction in emissions from “heavy-duty engines” compared with 2010 levels.

In South Asia, the areas with critically high PM2.5 concentrations that would benefit from an airshed approach include the western and central Indo-Gangetic Plain; the Brahmaputra basin (India and Bangladesh);

India Air Pollution continued on page 82

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