The severe air pollution episode that choked the National Capital Region and a substantial part of the Indo Gangetic Plain (IGP) this November, triggered the seasonal blame game. While the farmers of Haryana and Punjab, burning crop residues, got their share of blame for fouling up the air of Delhi, the infiltration of smoke plume across the international India-Pakistan border also hogged the headlines.

Every year, satellites spot swathes of smoke plumes across the region on both sides of the border when farmers burn the crop residues to clear the fields for sowing the next crop. This tips over the pollution curve that is already elevated due to the round-the-year emissions from combustion and dust sources of pollution across the regions and are trapped by the calm and cool atmospheric conditions of the winter.

As both Delhi and Lahore clamped down with temporary emergency measures to prevent the situation from worsening, what got lost in the din was the complex challenge of managing air quality in the complex geo-climatic conditions with overlapping airsheds that include the rapidly growing economies of South Asia. An airshed spans over a huge geographical tract with a nearly common air mass, geographical attributes and similar meteorology.

While the seasonal problem of winter pollution escalates as a noisy political drama, the science of air pollution warns us of a different challenge emerging from a deep connection between local and regional air quality.

It is clear from the emerging scientific evidence that local pollution does not remain confined within the boundaries of municipalities, cities, states or countries. Pollution blows with the wind. Studies are now proliferating in India, Nepal, Bangladesh Bhutan, Pakistan among others pointing towards the transboundary nature of pollution movement in South Asia.

Only city-based action won't work

This emerging evidence has challenged only city based action for clean air. It is clear that pollution from the larger airshed influences and undermines the local air pollution control efforts requiring cross-sector and multi-jurisdictional strategy within the country as well as between the countries.

A city cannot meet the clean air benchmark only with city based action. For instance, in Delhi and the National Capital region (NCR), that is fighting a difficult air pollution battle, the dynamic forecasting of the Indian Institute of Tropical Meteorology shows that nearly 70 per cent of its particulate concentration wafts in from a much larger catchment outside the city. Further studies such as the 2018 pollution source apportionment study of the Automotive Research Association of India and The Energy Research Institute (TERI) shows that during winter Delhi also contributes about 40 per cent of the pollution concentration in the satellite city of Noida on the downwind side.  

The same phenomenon plays out across the Indo-Gangetic Plain (IGP). Its unique meteorology, landlocked ecosystem and high pollution and population concentration complicate the implementation of solutions. It is challenging for any city or town in the IGP to meet the clean air targets if the regional clean-up is not achieved.

In fact the intervention of India’s National Green Tribunal in 2021 in this matter led to an integrated pollution assessment of the IGP by the expert committee under the Central Pollution Control Board (CPCB) that found that in the Indian IGP, Uttar Pradesh is the highest PM2.5 emitter, followed by West Bengal, Bihar, Punjab and Haryana. Industry, transport, household fuels, power plants, waste burning, construction etc spread across this region contribute towards the regional pollution.  This has led India's National Clean Air Programme (NCAP) to take on board the need for a comprehensive regional plan. An IGP programme is underway. 

Several critical airsheds

In the larger South Asia context, air pollution does not follow national boundaries and therefore the solutions for all the airsheds cannot come from any one city or a country. The countries in South Asia – India, Bangladesh, Nepal, and Pakistan - that share a common airshed are impacted by the transboundary pollution. According to a World bank estimate, more than half of the air pollution across major cities in South Asia is not local but transboundary in nature.

The World Bank has identified several critical airsheds that have high concentrations of particulate matter of less than 2.5 micron size (PM2.5). These areas include the western and central Indo-Gangetic Plain that extends into Pakistan; central and eastern Indo-Gangetic Plain that extends into Nepal and Bangladesh; the Brahmaputra airshed covering Bangladesh and India; middle India including east Gujarat, west Maharashtra, Odisha and Chhattisgarh; northern and central including Pakistan (Punjab), India (Punjab), and part of Afghanistan; south Pakistan; and west Afghanistan extending into east Iran.

Experts point out that in this region both transboundary and local pollution get trapped by the high-altitude Himalayan range that form a valley effect.  During winter, the Western Disturbances (a series of alternating low and high-pressure systems that travel from west to east, causing heavy haze and fog) further impact the IGP. Any increase in emissions in these regions have significantly deteriorated the region’s air quality. A lot of the movement of particulate matter and black carbon from these countries are also settling on mountains, snow and glaciers accelerating melting of snow or interfering with local rains in addition to harming the health.

Regional dialogues need reinvention

Transboundary impact of pollution across South Asian countries has triggered interest in regional action and cooperation. Some of the early efforts include the South Asia Cooperative Environment Programme (SACEP) for regional cooperation on air pollution mitigation in South Asia, which is well known as the Malé Declaration of 1998.  

India, Bangladesh, Bhutan, Iran, Maldives, Nepal, Pakistan and Sri Lanka came together to assess and analyse the origin and causes, nature, extent and effects of local and region­al air pollution; develop and/or adopt strategies to prevent and minimize air pollution; initiate cooperation on monitoring; and standardize methodologies to monitor acid depositions and assess impacts.  This sought common monitoring goals, information sharing systems, development of science for pollution source assessment and transboundary effects, and upward harmonization in policy action. This forum, however, needs reinvention and resources to become a more effective forum for regional dialogue and action.

In more recent times, several new dialogue processes have started mobilising the regional governments and the multilateral banks like the World Bank to also ramp up funding support for such efforts in the region. Post COVID 19 pandemic, the Kathmandu, Nepal regional science policy dialogue was held in 2022 to outline the roadmap. This was followed by the second dialogue in Thimpu, Bhutan in 2024 that brought together the governments of the IGP and Himalayan foothill countries.

Both these dialogues have focussed on the role of science and analytics in defining policy measures with transboundary approaches, promote technical cooperation, knowledge sharing, capacity building and accelerate actions to meet the National Ambient Air Quality Standards. There is also a proposal to consider an aspirational goal of “35 by 35” i.e. < 35 μg/m3 for annual PM2.5 concentrations by 2035.

The World Bank Group in its 2023 report[i] has estimated that coordinated measures across sectors and borders within South Asia can be 45 per cent less expensive than ad hoc measures without coordination and cooperation. The multi-jurisdiction and multi-sector roadmap will require significant funding and resource mobilisation including innovative financing.

What do other countries/regions do?

A global review carried out by the Centre for Science  and Environment[ii] (CSE) shows that globally, national governments have begun to develop such a framework for management of transboundary pollution within the country and between countries. The countries in South Asia also require a similar framework.'

In Europe the convention on Long-range Transboundary Air Pollution (LRTAP or Air Convention) allows signatory parties to agree to reduce emissions to the levels set based on their current exposure, available technologies, cost of implementation, and economic constraints. The Gothenburg Protocol (in its 2012 amended version) established national emission ceilings for ozone precursors and fine particulate matter (PM2.5 )for each country. The European  air quality policy and European Green Deal have called for the development of a zero-pollution action plan to improve air quality across the EU.

At the national level, the US delineates the Air Quality Control Regions under their Clean Air Act (CAA). There is a provision of "Good Neighbour"  in the Act to address interstate transport of pollutants to the downwind states. States have to make extra effort to reduce pollution from their sources to reduce downwind impact. Thus, meeting federal and state air quality targets in the downwind area is a joint effort.

China has also adopted regional approach by delineating clusters like Jing-jin-ji (Beijing-Tianjin-Hebei region (BTH) with 28 towns including Beijing), Yangtze River Delta (south Shanghai) and the Pearl River Delta (south Guangzhou and Shenzhen) – adopting the Jing-jin-ji air pollution management framework involving 26 provinces.

Air has no boundaries

Air pollution is a serious public health challenge in South Asia. According to the estimates of the State of Global Air, air pollution was responsible for 2.6 million deaths in this region in 2021.  This growing risk requires harmonised action and a cooperation model to ramp up airshed-wide action on monitoring and scientific assessment of the problem,  mitigation from key sources of pollution including vehicles, industry, power plants, solid waste, household cooking, brick kilns and a range of dispersed sources.

Science has established that it is not possible for any one city, or state or even a country to meet the clean air benchmark without minimizing the regional influence. Airshed level control strategies are  necessary to meet the clean air targets. Air has no boundaries and action cannot be siloed.

(The author is the Executive Director, Research and Advocacy, Centre for Science and Environment, India. Views expressed are personal. Her X handle is @AnumitaRoychowd and LinkedIn Anumita Roychowdhury)

[i]  World Bank, 2023, Striving for Clean Air, Air pollution and public health in South Asia,  
[ii] Centre for Science and Environment, 2021, Managing regional air quality: Need for a framework