It is that time of the year when Delhi is covered with haze and smoke. The extremely bad air quality in Delhi during this time is attributed mainly to the widespread burning of agricultural waste in the villages of neighbouring states of Punjab and Haryana, as farmers in these areas try to quickly prepare their fields for their next crop.
But while Delhi has been choking for the last few days, as it usually does every year during this time, Chandigarh, the capital of both Punjab and Haryana and located right in the heart of the stubble-burning zone, has had relatively clean air.
According to CPCB data, the air quality index (AQI) in Delhi around 2.30 pm on November 2 was 402, while Chandigarh was relatively clean at 281. And at 4 pm on November 1, CPCB data show, the AQI in Delhi (average of the past 24 hours) was 484 (Severe), while the corresponding figure for Chandigarh was 254 (Poor).
If stubble-burning is the major reason for Delhi’s terrible air, as Chief Minister Arvind Kejriwal has been saying, why is it that the smoke from the burning fields has left Chandigarh alone?
In fact, this is not surprising.
Chandigarh escapes the agony of Delhi because of its geographical location and the direction of wind that blows during this season.
Chandigarh lies almost directly north of Delhi, while the wind, coming from across the border over Lahore, blows from northwest towards southeast.
This is the same corridor that the moisture-laden western disturbance also takes.
Chandigarh sometimes sits on the edges of this corridor, or just outside of it.
Also, most of the stubble burning happens in the area that lies between the latitudes of Delhi and Chandigarh. It is the wind that brings the smoke from agriculture burning to Delhi. The wind is directed towards Delhi, and not towards Chandigarh.
But the wind does not stop in Delhi.
It moves through the Gangetic plains of Uttar Pradesh and Bihar, and consequently, the towns and cities in these areas also suffer some of the consequences of stubble-burning in northwest.
In fact, the cities of Kanpur and Lucknow have had pretty bad air quality in the last few days, along with Delhi. The AQI in Kanpur on November 2 afternoon, according to CPCB data, was 384, and that in Lucknow was 420, worse than even Delhi.
Same is the case with areas in western Uttar Pradesh adjoining Delhi — places like Aligarh and Agra. On Friday, Uttar Pradesh Chief Minister Yogi Adityanath directed local officials to take steps to curb air pollution in these cities.
Last year, the WHO had come out with a global report that had revealed that 14 of the 15 cities in the world with the highest concentration of PM2.5 levels were in India.
Ten of these cities were in this same Gangetic belt. This included places like cities far off from Delhi like Patna, Gaya, Varanasi and Muzaffarpur, which are not known for having local sources of very high pollution.
Studies have shown that these places do not generate even half the pollutants that are measured there. It is the wind that carries pollutants generated in ‘up-wind’ areas to these places.
“In this region, wind predominantly blows from north-west to east for most of the year but more so in the winters, carrying along with it pollutants generated elsewhere. Even the pollutants found over Delhi are not all generated in Delhi, but transported from other places. We have published papers to show that more than 60 per cent of the particulate matter found in Kanpur have been generated elsewhere,” Sachidanand Tripathi of IIT Kanpur had then said.