DELHI does not have the dirtiest air in the world. According to the 2018 ranking of 4,500 cities by the World Health Organisation, that distinction goes to Kanpur, another of the north Indian towns that occupy the top 14 spots on the list. But with 25m people Delhi is far bigger than the others, so its pollution endangers more lives. Dirty air kills some 30,000 Delhi-wallahs a year—and that is a low estimate, some doctors say, if you count for effects as varied as higher rates of lung cancer, diabetes, premature births and, according to recent research, even autism. Delhi’s daily average level of suspended PM2.5—fine dust—is six times what the WHO regards as the maximum safe concentration. In winter it is higher and in the weeks after Diwali, an autumn festival of lights (and firecrackers), it can rise above 50 times the WHO limit. Why is Delhi so polluted?
The answers are as layered as the smog itself. One problem is geography. The flat, fertile plain where Delhi sits is bounded by the Himalayas, which block the movement of air. In summer, intense heat creates an updraft, lifting smog to altitudes where monsoon winds off the Indian Ocean can largely disperse it. But in winter, morning mist traps particles at ground level. There is rarely a breeze, but even so colder air coming off the mountains creates a lid effect. Dust and smoke accumulate and hang. Where do they come from? Aside from the ordinary dustiness of a hot country that is under constant construction and has tens of millions moving along poorly paved roads, there are the airborne effluents of coal-fired power plants, crematoria, fire-cleared rice paddies, factories and furnaces burning cheap pet coke and furnace oil, millions of poorly tuned vehicles running on low-grade fuel, diesel-powered locomotives and generators, and cooking stoves fed by cow dung and wood.
Poverty exacerbates the challenge. It is not easy, for instance, to get farmers to use costly machines to prepare fields for planting wheat after the autumn rice harvest, instead of simply burning off the rice stubble. But policies have sometimes made things worse. Pushing for self-sufficiency in energy, successive governments have favoured coal-fired power over cleaner plants. They have also kept diesel cheaper than petrol, a vote-getting sop to farmers who run diesel tractors and pumps. The result: millions of stinky, diesel-powered vehicles fill Indian cities, after carmakers and buyers shifted to the more “economical” fuel. Another example: faced ten years ago with a frightening fall in groundwater levels, states in north-west India’s rice belt forced farmers to delay planting until well into the monsoon. The water table did stabilise. But the delay also pushed back the harvest. Now, when farmers burn rice stubble, the tail of the monsoon has already passed. With no wind to disperse it, the smoke drifts idly south-east, converging in the skies over Delhi.
Unlike Beijing, whose efforts to purge itself of smog have made impressive headway, India’s capital is not run by top-down command. The city’s government is not only slowed by elections, but by a structure of overlapping jurisdictions so convoluted it seems designed to fail. Even so, some progress has been made. For more than 15 years most buses, taxis and auto-rickshaws have run on natural gas. Polluting industries and coal-fired power plants have been shut down, and a project to distribute domestic cooking gas to replace solid fuels has grown. This year the national government banned imports of dirtier industrial fuels, and introduced higher-octane petrol and diesel in the capital. By 2020 all new cars sold in India will have to conform to much cleaner emissions standards. State governments are pushing harder to stop farmers burning their fields. As the smog thickened dangerously again this month, Delhi’s own government banned lorries from entering the city and ordered a halt to construction projects. Some day, a concerted combination of such steps may actually bring blue skies back to India’s capital. The question is, when?