Why is Dehradun's air quality worsening?

Wind speed not strong enough to push away the pollutants

air pollution Representational image | PTI

Dehradun is grappling with worsening air quality for the second year in a row because of a surge in vehicular traffic and construction activity. The capital of Uttarakhand lies in a valley; this traps pollutants thus exacerbating the problem.

The average PM2.5 levels surpassed the permissible limit in both 2021 and 2022, measuring at 48.65 µg/m3 and 45.88 µg/m3, respectively. The Central Pollution Control Board (CPCB) of India recommends an annual average limit of 40 µg/m3 for PM2.5, which was exceeded in both years. Additionally, the World Health Organisation (WHO) advises that annual average concentrations of PM2.5 should not surpass 5 µg/m3.

As the monsoons are over and autumn knocks, winds across the northwest region become calm, and temperatures start dipping. Both these factors contribute to the inability of pollutant matter to move upwards and disperse.

Mahesh Palawat, Vice President - Meteorology and Climate Change, Skymet Weather said, “Weather conditions are presently very conducive. Temperatures have also started coming down, leading to the formation of mist and haze during the morning hours. The mist contains water vapour where the pollutants get deposited and remain suspended near the earth's surface. Further, the absence of any weather activity, as well as light winds, are not letting pollutants move away.”

As temperatures fall, there will be more bad air days in Dehradun as the inversion layer will thicken. This layer refers to a blanket of the atmosphere in which temperatures rise with height, thus preventing the air below it from rising, and trapping any pollutants.

In addition, the Western disturbance (WD) has not seen any movement since October 12. Uttarakhand recorded 20.2mm of rain against the normal average of 33.6mm of rain from October 1 to November 9, resulting in a deficiency to the tune of 40 per cent.

In the absence of any weather activity, wind speed continues to be light and not good enough to push away the pollutants.

Expert studies have warned that winter precipitation in northern India and Pakistan is projected to decrease over (by as much as 10-20 per cent) the coming century. This will change the precipitation climatology of the region and also give rise to extreme weather conditions.

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