A new global report on air pollution by the World Health Organisation (WHO) shows that 14 of the 15 cities with the highest levels of PM 2.5 pollutants in 2016 were in India. (The 15th was Ali Subah Al-Salem in Kuwait.) These 14 towns and cities stud a broad swathe of northern India stretching west to east from Jodhpur (No. 14) in Rajasthan to Gaya (No. 4), Patna (No. 5), and Muzaffarpur (No. 9) in Bihar. Effectively then, the new WHO report identifies the Indo-Gangetic plain, along with Rajasthan and the Kashmir Valley, as having the worst air in the world.
That’s rather odd. Or is it?
While Delhi, Agra and Kanpur are known to have very high levels of air pollution, places like Varanasi, Muzaffarpur, Gaya, and Srinagar — all on the list of the 15 most-polluted — do not have a high concentration of polluting industries, or other common sources of pollution, such as vehicular emissions. And yet, experts are not entirely surprised by the high levels of PM 2.5 recorded at these places.
“We have been noticing a steady rise in the particulate matter over the Gangetic plains for the last one decade or so. It is very well documented and published. This is not something new or surprising. Even satellite pictures have been showing that the Gangetic plains are emerging as one of major hotspots for air pollution,” Prof Sachchidanand Tripathi, an atmospheric sciences expert at IIT Kanpur, said.
Trapped in Valley, no way out
Scientists like Prof Tripathi and Dr Gufran Beig of the Pune-based Indian Institute of Tropical Meteorology point out that the Gangetic plains are like an enormous valley, trapped between the Himalayas in the north and the Vindhyas in the south, from where pollutants are unable to disperse very far. “It would seem like a very wide valley, but for purposes of dispersion of air pollutants, this is what it is, a valley,” Prof Tripathi said.
Added is the fact that the region is one of the most densely populated in the world. “The sheer number of people is so high, in excess of 600 million, that the demand for energy sources, and the consequent burning of fuels, is extremely high. That would release a large number of pollutants and particulate matter in the air,” he said.
Dr Anumita Roy Chowdhury, head of the air pollution and clean transportation programme at the Delhi-based advocacy organisation Centre for Science and Environment, said, “This region is land-locked — pollution cannot dissipate quickly — and does not have the advantage of the coast like Mumbai or Chennai. Also, a lot of the smaller cities have poor waste management, there is a lot of burning, solid fuel use, they are moving from non-motorised to motorised transport. Chulhas, we know, contribute to 25% outdoor pollution in India.”
But this is still only part of the story. It still does not explain why Gaya or Muzaffarpur should have such high levels of PM 2.5. According to Prof Tripathi and other scientists, neither Gaya nor Muzaffarpur — and not even Kanpur or Delhi — produce even half of the pollutants measured in these cities.
Also read | What is PM 2.5?
“You have to account for the wind direction. In this region, wind predominantly blows from north-west to east for most of the year, but more so in the winter, carrying along with it pollutants generated elsewhere. Even the pollutants found over Delhi are not all generated in Delhi, but transported from other places. We have published papers to show that more than 60% of the particulate matter found in Kanpur have been generated elsewhere,” Prof Tripathi said.
Once the pollutants enter the Gangetic region, they get trapped, and remain suspended over the area. Most of the particles measured at Gaya and Muzaffarpur, therefore, are the ones that have been transported from “up-wind” states. As they move from west to east, these particles gain in size and mass. Gases released from industries or vehicles, too, condense and are converted into particles.
“The high levels of humidity in this region is very conducive to the formation of secondary aerosols. Water facilitates the reaction between the emitted gases whose molecules form clusters and slowly nucleate into particles,” Prof Tripathi said.
Is it a fait accompli, then?
No, North India is not destined to breathe polluted air. This is not the only part of the world with these or similar geographical constraints. There are international models in which similarly placed states/regions have laws that empower governments to invoke stringent measures whenever required. California, for example, is a valley with a propensity for pollution to build up — and it was the first state in the US to enact an anti-pollution law back in the 1940s.
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