Which is the most polluted city in north India?

New Delhi, Dec 16: Ghaziabad is the most polluted city in north India and its annual average PM2.5 levels are much worse than those of Delhi, according to data from 137 continuous ambient air quality monitoring stations (CAAQMS) spread across 56 cities in the region.

The Centre for Science and Environment, which analysed the PM2.5 data from these CAAQMS from January 1, 2019, to November 30, 2021, also said PM2.5 levels in otherwise cleaner smaller towns can exceed the concentration reported in Delhi during smog episodes in early winters.

In its most polluted week, Ghaziabad recorded an average PM2.5 level of 360 micrograms per cubic metre (ug/m3), while the annual average level stood at 110 ug/m3, the highest in north India.

Delhi's annual average PM2.5 levels stood at 97 ug/m3 and the weekly levels were 270 ug/m3. Moradabad, Noida, Faridabad and Gurugram recorded their annual average PM2.5 levels at 96 ug/m3, 92 ug/m3, 89 ug/m3 and 88 ug/m3, respectively. Chandigarh recorded the lowest annual average levels at 37 ug/m3, followed by 39 ug/m3 in Bathinda.

Most of the smaller towns have considerably lower annual average PM2.5 levels but during early winter, when the entire region gets engulfed by smog, smaller towns report levels comparable to Delhi, the green think tank said.

For instance, smaller cities like Vrindavan, Agra and Firozabad have comparatively lower annual average PM2.5 levels than Delhi. But during the early winter this year, their weekly average PM2.5 levels exceeded those of the national capital.

The annual average PM2.5 level of Delhi and Agra is 97 ug/m3 and 78 ug/m3, respectively. But during the early winter this year, the weekly average PM2.5 level in Agra was 282 ug/m3 -- five per cent more than Delhi's 270 ug/m3.