Think outside the city to manage urban pollution

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 (PM_2.5). 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 PM_2.5 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 PM_2.5 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.