States neighbouring Delhi recorded the highest farm fire count on Monday, but it had a small impact on the national capital's air quality, mainly due to strong transport-level winds, the Ministry of Earth Sciences' air quality monitor, SAFAR, said.
According to SAFAR, states bordering Delhi recorded 4,962 farm fires on Monday, but the share of smoke from crop residue burning in Delhi's PM2.5 concentration was just 14 per cent and came down to 12 per cent on Tuesday.
However, the concentration is expected to increase to 19 per cent on Wednesday, it said.
The government's air quality monitoring and forecasting service said though Monday's farm fire count was the highest for the season and the wind direction was northwesterly, Delhi's air quality "continued to recover".
It was mainly due to faster transport-level winds (40 kilometres per hour) that "rapidly passed over Delhi without descending", SAFAR said.
It's an illustrative example as to how a combination of several factors like external transport, local emission, and boundary-layer dynamics act together to have a powerful impact, it said.
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However, air quality is likely to deteriorate to the higher end of 'very poor' category or the lower end of 'severe' category during "stable late-night hours and early hours of Wednesday due to reduced wind speed".
SAFAR said a fresh western disturbance is approaching north India and a change in surface and boundary-layer wind direction is expected by November 7. This will reduce transport of stubble fire plume.
"Scattered rainfall is expected to further improve AQI to the lower end of the 'very poor' or the 'poor' category by November 8," it said.