Think outside the city to manage urban pollution

Only around 40% of the fine particulate matter pollution in Delhi originates from within the city, and about 60% percent is transported from outside, an IIASA study found. This illustrates the problem with focusing on urban areas when looking for solutions to air pollution. To address this, the IIASA Air Quality and Greenhouse Gases Program (AIR) has developed a blueprint for managing air pollution in fast-growing megacities in developing countries, showing that effective solutions require regional and multi-sectoral cooperation.

As most people live in cities, air pollution is widely considered an urban problem, and traditionally solutions are sought at the urban level. However, air pollution can travel over long distances, and conventional solutions that deal with air pollution on a local level, such as policy responses by city administrations, cannot deliver effective solutions.

Contributions from different sources to population exposure to PM2.5 in Delhi, 2015. Uttar Pradesh is an Indian state that borders Delhi NCT (the National Capital Territory of Delhi).

In a joint project with the Indian Institute for Environmental Engineering Research, AIR used its Delhi -specific Greenhouse Gas – Air Pollution Interactions and Synergies model (GAINS-Delhi) to explore management options that could efficiently improve air quality in the city, with a focus on fine particulate matter pollution (PM2.5). The work also provides a blueprint for managing air pollution in other fast-growing megacities in developing countries.

Despite the large size of Delhi, currently about 18 million inhabitants, only around 40% of the PM2.5 the population is exposed to originates from local emissions, about 60% percent is transported into the city from outside, the study found. Contrary to widespread belief, traffic contributes only about 15-20% of the PM2.5 the population is exposed to. In fact, the majority originates from a combination of other sources, including households, small-scale industries and workshops, trash burning, agriculture, and fireworks.

Recent regulations to control emissions from large individual sources in the surrounding areas should stabilize the pollution coming into the city, the researchers found. However, the decline in particulate matter in exhaust gas as a result of new traffic standards in Delhi is likely to be negated by non-exhaust emissions—such as road dust, and tire and brake wear—that will increase along with the expected growth in traffic volumes. The anticipated economic growth is also likely to counteract the benefits of the ambitious pollution control measures adopted by the authorities. As a consequence, the researchers conclude, air quality will continue to deteriorate.


[1] Amann M, Purohit P, Bhanarkar AD, Bertok I, Borken-Kleefeld J, Cofala J, Heyes C, Kiesewetter G, et al. (2017). Managing future air quality in megacities: A case study for Delhi. Atmospheric Environment: 1-28.


  • Indian Institute for Environmental Engineering Research