Delhi air pollution: Smog season has just started, will continue throughout winter, says US weather forecaster

Washington: Cities in north India and Pakistan will continue to experience dangerous level of smog-filled pollution over the next several months as the region is just entering its smog season, a top American atmospheric organisation has said.

"This is just the start of the smog season in northern India and Pakistan, and will last for much of the upcoming winter. That means there are plenty of more opportunities for cold, stagnant air to fill with pollution, turning cities into dangerously unhealthy snow globes," said the National Oceanic and Atmospheric Administration (NOAA) in a statement on Wednesday.

NOAA released satellite pictures and explained the reasons behind such a polluting atmosphere in major parts of north India and Pakistan. Widespread smog caused by combustion of fuels and burning of crops and fires made it dangerous to be outdoors in cities in northern India and Pakistan, it said.

Delhi has been battling crippling smog and air pollution for a week. PTI

Delhi has been battling crippling smog and air pollution for a week. PTI

For air to get this polluted, in addition to needing a good amount of human help from the combustion of fuels and burning of crops and garbage, there needs to be specific atmospheric conditions that let the air remain still enough for pollution accumulate, it said.

"This stagnation occurs when there is an inversion layer in the atmosphere," NOAA said.

An inversion layer refers to instances where the air does not cool as one moves up in the atmosphere, it explained. "Instead, warmer air sits on top of denser, colder air near the ground. Since that cold air has no place to go thanks to the warm lid placed atop it, it just sits there gathering pollution like a hazy snow-globe," NOAA said.

So, in late fall across the Indian sub-continent, the Northeast Monsoon is beginning to take hold, it said, adding that, the monsoon is driven by temperatures differences between the land and surrounding waters.

At this time of the year, the large landmass to the north begins to cool down considerably forming a dense, cold air mass known as the Siberia high pressure system. Meanwhile the waters off of India remain warm. This contrast draws northerly winds across northern India, bringing cold air down off the Tibetan plateau. The cold air settles into the valleys, creating inversions, NOAA said.

Referring to satellite images, it said the widespread burning of crop fields in northern India contributed to dangerous levels of air pollution in cities across northern India and Pakistan.

At the US Embassy in New Delhi, hourly AQI values for PM2.5 taken from 7 November to 10 November exceeded 500 with an
astounding recording of 1010 at 4 pm on 8 November. Hourly readings still peaked in the 'Hazardous' category (301-500 AQI) through 14 November.

Meanwhile, the highest hourly AQI value in the US on 14 November was around 150 in Hidden Valley, Arizona, it said.

Updated Date: Nov 16, 2017 08:25 AM

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