Why Delhi’s air is choking its residents

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This is an excerpt from Choked by Pallavi Aiyar. Get the full book tomorrow on the Juggernaut App. 

In 2014, a WHO study ranked Delhi as the world’s most polluted city. Neither Beijing nor any other Chinese city even figured in the top twenty, but thirteen Indian cities did. These were Patna, Gwalior, Raipur, Ahmedabad, Lucknow, Kanpur, Firozabad, Amritsar, Ludhiana, Allahabad, Agra, Khanna and, of course, Delhi.. This ranking was based on PM 2.5 levels…


Pollution is also affected by seasonal variations. As any resident in north India can attest, the “pollution season” coincides with winter. When temperatures drop, an “inversion” occurs, whereby a dense band of cold air gets trapped under a layer of warm air. The warm layer acts much like a lid, trapping pollutants near the ground. There is also a sharp increase in burning of both biomass, like leaves and twigs, and trash for heating. This burning contributes to as much as 30 percent of particulate pollution in winter (in summer, biomass accounts for much less of particulate pollution). It is particulate matter that registers a massive rise in the winter, rather than gases like NOx, which are more strongly associated with vehicular and industrial pollution.

Another external factor that contributes to toxic air in the early winter is the clearing of agricultural land, post-harvest, in the surrounding areas of Haryana and Punjab. Finally, as in Beijing, geography also plays a role in explaining Delhi’s dirty air, as well as the toxic air in inland cities like Ahmedabad, Patna, Lucknow and Ludhiana. Both the Chinese and Indian capitals are landlocked megacities with few avenues for flushing polluted air out the city (unlike, say, Shanghai or Mumbai). Delhi, like Beijing, is located in a highly polluted region. The capital city is affected by the industrial and agricultural activity in its air shed. Most brick kilns, for example, are not located in the city proper, but in upwind industrial areas in the neighbourhood. These kilns are particularly polluting because they burn coal, wood and other organic smoky materials for baking the bricks that serve the construction boom in the capital.


The worst air of all occurs in Delhi during the lead up to the festival of Diwali, which is celebrated in either October or November. Particulate matter tends to double from the already foul levels. In 2015, Diwali saw PM 10 levels in Delhi rise to between 1,000 and 2,000 micrograms per cubic meter. It is almost impossible to conceive of such numbers. The mind cannot compute them and nor can most pollution monitoring devices. (The WHO safe limit for average PM 10 over a 24-hour period is 50 micrograms per cubic meter). Levels of potassium, barium, sodium, and zinc, the main components of firecrackers, also spike to several times the norm…

The air that winter in Delhi was like caustic pea soup. Suddenly I was less keen on taking the kids to gambol about the city’s gardens and historic monuments. I watched them for signs of dripping noses. Their coughs sounded dry and hollow. I had been worried about dengue fever and had carried armloads of mosquito repellent and citronella patches with me, but my boys were without protection against the most ubiquitous health hazard of all — the air.


Read Choked! Inside the World’s Most Polluted Cities on the Juggernaut app tomorrow. 


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