Stubble burning in Haryana and Punjab in itself would not have triggered the nearly week-long smog episode in the national capital, had wind not blown from the north west region, a government agency has said even as it predicted further improvement in air quality.
In fact, when level of PM 2.5 (particules measuring less than 2.5 microns) had peaked to 693 micrograms per cubic metre (ug/m3) on October 31, the day after Diwali, the contribution of smoke from stubble burning was negligible, although farm fires were raging even then.
The main factors that influence Delhi's air quality are wind speed and wind direction, and if the two remain favourable, chances of pollution peaking to extreme levels, as seen last week, are "rare".
The 24-hour-average (rolling) of PM 2.5 and PM 10 further came down to 295 and 474 micrograms per cubic metre today. The prescribed standards is 60 and 100 respectively.
Despite recording a steep fall, the AQI graph continues to be in the "severe" category. It is expected to turn "very poor", a shade better, tomorrow.
Wind speed picked up further as it blew at an average speed of 10 km/hr in the city helping disperse the pollutants and the city basked in sunshine for the second consecutive day.
"Until November 1, contribution of biomass burning was insignificant, almost nil. However, from November 2, its percentage started to increase due to change in wind pattern. It peaked to 70 per cent on Sunday when wind became NNW (north-northwest).
"Today winds are mainly westerly and contribution of biomass has gone down to less than 10 per cent. This is how weather is playing with Delhi's air quality these days," a SAFAR scientist said.
Early this year, a team led by IIT-Kanpur Professor Mukesh Sharma had submitted a report titled 'Comprehensive Study on Air Pollution and Green House Gases (GHGs) in Delhi'.
The widely quoted report had put the contribution (average) of biomass burning in pollution within the city (during winters) at 17 per cent (for PM 10) and 26 per cent (for PM 2.5).
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