The harvest of polluted air

Context-

The haze and smoke over Delhi, which has become an annual event for about three weeks in October-November, has triggered a temporary ban on construction activities and the movement of trucks and diesel four-wheelers that do not comply with BS-VI norms.
The Supreme Court will hear a petition on agricultural stubble burning in the northern states, considered the prime reason for the extremely bad air quality in Delhi-NCR.

Is agricultural burning the main culprit?

While the region’s own pollution sources are a problem, stubble burning was an important factor in the deterioration of air quality in October-end and November.
At this time of the year, the burning of agricultural waste in Punjab and Haryana contributes 30-40% of the PM2.5 concentrations in Delhi’s air.
It is the single largest source of PM2.5 levels on most days during this period.
The concerted straw burning happens over a period of 10-15 days in 7-10 districts. The wind direction is also north-westerly and brings the plume of smoke from Punjab, through Haryana, to Delhi and then onwards to Kanpur and beyond.
According to IARI’s paddy straw burning monitoring portal, over 26,000 fire incidents have been observed in Punjab since September 15. In Haryana, 2,440 incidents have been observed.
Agricultural waste burning in Punjab and Haryana happens in the months of May and June as well but at that time, it accounts for about 15-20% of PM2.5 concentrations in Delhi’s air. So the air quality over the capital does not become this bad.

Role of weather in the rising pollution levels-

Weather plays a critical role as well — a 30-40% rise in pollutants at any other time of the year would not cause the same impact.
Hotter air rises higher above the surface and takes the pollutants along with it.
The polluting particles are lifted 2-3 km above the surface or even higher, before getting dispersed.
But during October-November the air is not that hot.
The pollutants are trapped and tend to get concentrated at lower levels of the atmosphere, resulting in the smoke and haze situation.

Delhi’s geographical location also makes it more susceptible to pollution-

With the Deccan Plateau, 500 km to its south and the Himalayas to its north, the region that stretches from Haryana to Bihar is a valley between two large structures.
Delhi, moreover, sits on the Aravallis, which has an elevation of a few hundred metres.
This makes Delhi a tabletop city of sorts.
It has a peculiar geography within the Indo-Gangetic Plains, landlocked from all sides.
This makes it more susceptible to these critical episodes.

But why is agricultural waste burned?

This waste is the remains of the paddy crop after it has been harvested.
This kind of burning is not specific only to Punjab or Haryana. However, the scale of burning in these states is much bigger than elsewhere.
Even in these states, this practice is relatively new. Even 10 years ago, the crop-burning problem was not this acute.
The burning is necessitated by the need to prepare the fields for the next crop in a very short window of time.
Due to a slight shift in the cropping pattern in these states, there is now very little time between the harvesting of one crop and the planting of the next crop.
The traditional method of manually uprooting, or cutting, the stumps of the previous crop is time-consuming and can delay the sowing of the next crop.
So farmers resort to the easier option of burning these remains.

Would the ban on construction and diesel vehicles work?

Construction has a small contribution to PM2.5 concentration.
The particles released from these activities are usually larger and add to PM10 concentrations.
The banning of construction is unlikely to have any significant impact on the prevailing situation.
Diesel vehicles, particularly older trucks, are indeed important contributors to high PM2.5 levels so a ban on their movement can help in improving the situation.
However, trucks are not allowed to move inside Delhi during the day in any case.

Is there no remedy for this situation?

Several solutions have been suggested and are being tried, for example, changing the crop cycle, deployment of mechanised equipment for harvesting that would render burning unnecessary, and conversion of this waste into something more useful, like a source of energy, which can become an incentive for not burning.
Experts over the years have suggested that farmers should move away from growing paddy in the quantities that they do, and shift to other crops such as maize, cotton, pulses and oil seeds.

To deal with the issue of stubble burning states, especially Punjab, should look at crop diversification.