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 the combustion of fuels, and the burning of crops and fires made it dangerous to be outside in cities in northern India and Pakistan, it said.
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 to 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 Northeast monsoon is driven by temperatures differences between the land and surrounding waters.
At this time of 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, NOAA 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 on November 7 through 10 exceeded 500 with an astounding recording of 1010 at 4PM local time on November 8.
Hourly readings still peaked in the Hazardous category (301-500 AQI) through November 14.
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