Delhi's air quality improved further on Tuesday, giving respite to people suffering from acute pollution for a week and the trend is likely to continue for a couple of days.
The air quality index dropped from 365 at 9.45 am to 331 at 3.45 pm, according to the Central Pollution Control Board.
In the National Capital Region, Greater Noida (348), Noida (358), Ghaziabad (351), Faridabad (311) and Gurgaon (328) also recorded improvement in air quality.
An AQI between 0-50 is considered 'good', 51-100 'satisfactory', 101-200 'moderate', 201-300 'poor', 301-400 'very poor' and 401-500 'severe'. An AQI above 500 falls in the 'severe plus' category.
The India Meteorological Department said winds gusting up to 25 kmph were flushing out pollutants faster.
"There are good chances of rains in northwest India on Wednesday night and Thursday due to a western disturbance. The precipitation will cover Delhi-NCR, Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Punjab Haryana, Rajasthan and western Uttar Pradesh," said Kuldeep Srivastava, the head of IMD's regional weather forecasting centre.
He said the situation will not be similar to that of Sunday when high humidity due to light rains led to the formation of more potent secondary particles.
Secondary particles are product of complicated atmospheric reactions between primary particles such as particulate matter, sulphur dioxide and nitrogen dioxide directly emitted by stubble burning and vehicles in the presence of other factors such as sunlight and moisture.
Examples of secondary particles include sulphates, nitrates, ozone and organic aerosols.
Srivastava said visibility levels improved to 3,000-3,500 metres in the afternoon, which is considered normal.
The Ministry of Earth Sciences' air quality monitor, SAFAR, said, "The AQI is back to 'very poor' category after rapidly recovering from 'severe' largely due to faster boundary layer winds (40 kmph)."
Though Haryana and Punjab recorded 4,962 farm fires, the season's highest, on Monday and north westerly winds, which carry smoke from stubble burning, continued to blow, Delhi air quality's "continued to recover", it said.
"It was mainly due to high transport-level wind speed which rapidly passed over Delhi without descending," SAFAR said.
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