Why Delhi air turns poisonous every winter

NEW DELHI: Smog ... Dust ... Soot ... Smoke. As the winter season sets in, Delhi has yet again turned into a "gas chamber" with a thick envolope of smog descending on the city, triggering health concerns among citizens and blame-game between governments.
On Thursday, smog in New Delhi hit "hazardous" levels as smoke from thousands of crop fires in northern India combined with other pollutants to create a noxious grey cocktail enveloping the megacity.

Just to understand how bad the situation really is, levels of the most dangerous particles — PM2.5, so tiny they can enter the bloodstream — were 588 per cubic metre early on Thursday morning, according to monitoring firm IQAir.
That is almost 40 times the daily maximum recommended by the World Health Organization.
According to Central Pollution Control Board (CPCB), it's not just Delhi that's breathing the toxic cocktail of pollutants but several other nothern cities.
The alarming figures are now stoking concerns among the people but the story of Delhi's toxic air is not new. In fact, it has been quite the same for several years now.
Why does Delhi turn into 'gas chamber' each year?
Environment minister Bhupender Yadav recently took a dig at AAP, blaming the governments in Punjab and Delhi for turning the national capital into a "gas chamber".
Politics aside, the fact that Delhi faces a similar dilemma each year is now turning into an issue of national concern.

Stubble burning
Crop fires are undoubtedly the biggest contributor towards air pollution in Delhi.
The burning of rice paddies after harvests across Punjab and other states persists every year despite efforts to persuade farmers to use different methods.
Like every year, data shows that stubble burning has gone up considerably in the last 30 days.
This is because farmers have to clear their fields ahead of the rabi season and burning of stubble is an efficient - and quickest - way to do it.

Typically, the farmers only have a short one week window to clear the land.
Punjab's groundwater issue
The widespread stubble burning in Punjab is actually a groundwater issue.
In Punjab, farmers are prohibited from planting paddy in May in order to prevent groundwater levels from going low before the monsoons. Groundwater depleting is turning into a big problem in Punjab and paddy is a water-intensive crop.

Thus, farmers in Punjab can only plant paddy from mid-June onwards. This has a cascading effect.
Due to the late sowing, the crops are harvested only in late October/early November. This coincides with the onset of winter season in north India when wind speeds slow down and temperatures drop.
If the sowing happened in May, the crops would harvest in September, which is windier and warmer in comparison.
Plus, it also means that farmers don't get much time to plant rabi crops before the winter season so the window for paddy stubble burning is rather narrow.

Lack of machinery and knowledge
Most farmers in Punjab are poor and cannot afford machinery for clearing out stubble in the ground. They are left with no option but to resort to the cheaper solution of stubble burning.
Plus, there is reticence about the alternatives, especially among small farmers, because they “too cumbersome”.
Meanwhile, the share of stubble burning in Delhi's PM2.5 pollution jumped to 38 per cent on Thursday.
Punjab had on Wednesday reported 3,634 farm fires, the highest this season so far, though their share in Delhi PM2.5 pollution stood at just 12 per cent due to unfavourable transport-level wind speed.
The number of farm fires stood at 1,842 on Tuesday, 2,131 on Monday, 1,761 on Sunday, 1,898 on Saturday and 2,067 on Friday.
Last year, the share of farm fires in Delhi's PM 2.5 pollution peaked to 48 per cent on November 7.
Around 53 per cent of the Delhi-NCR residents identify stubble burning in neighbouring states as the "primary cause" of rising levels of air pollution, according to a LocalCircles survey.
(With inputs from agencies)