Delayed monsoon withdrawal, wind direction ensure cleanest October air since 2018 in Delhi

This October, Delhi witnessed the cleanest air for the month since at least 2018, The Indian Express reported. The average air quality index was 173 during the month, an improvement from last year’s 265. The figures for the corresponding periods in 2019 and 2020 were 233 and 268, respectively.

Experts attributed the improvement in air quality to record rainfall this monsoon. Delhi also witnessed record rainfall this October due to the delayed withdrawal of the monsoon current and the presence of a western disturbance.

Central Pollution Control Board (CPCB) bulletins indicate that there were no ‘very poor’ or ‘severe’ AQI days for Delhi this October. In contrast, there were nine ‘very poor’ air days in October 2020, five in 2019, and nine in 2018. In 2019, there were two ‘severe’ AQI days, while 2018 registered one such day.

Delhi’s first ‘good’ air day last month was on October 18 when the AQI hit 46. Delhi had not recorded a single ‘good’ air day in October since 2018. This year, there were also three ‘satisfactory’ AQI days in October. There were no such days recorded in October 2018 and 2020.

Active farm fires up in Haryana, Punjab
Active fire events in Haryana and Punjab have risen over the past few days, after registering a decline around October 24 and 25 when the prevailing western disturbance caused rainfall over parts of northwest India.

The share of crop residue burning to PM 2.5 levels has witnessed a decline in Delhi recently since wind direction was not favourable for the transport of pollutants, scientists associated with the System of Air Quality and Weather Forecasting and Research (SAFAR) forecasting system told The Indian Express.

According to the CPCB bulletin, there were 1,353 active fire events in Punjab on October 29 — the highest for a single day since at least October 16.

In Punjab, the active fire count has been witnessing a steady increase from October 26. There were 76 fire events on October 25. That figure rose to 329 on October 26 and 279 the following day. The active fire event count rose to 761 on October 28, and breached the 1,000-mark barrier on October 29. October 22, with 1,111 recorded fire events, was the last time that the count breached 1,000 this year.

In the case of Haryana, the active fire count was 161 on October 29, 134 on October 28, and 93 on October 27.

On Sunday, Delhi’s air quality remained ‘poor’ for the fifth successive day as the AQI hit 289. The contribution of stubble burning to PM 2.5 levels was 8% on Sunday. The ratio was 12% on October 30 and 20% on October 29.

The recent shift in wind direction explains the low contribution of stubble burning to pollutants in the national capital. The Air Quality Early Warning System has predicted wind direction from the southeast of Delhi today and on Tuesday. Pollutants from stubble burning usually reach Delhi when the wind flows from the northwest or west.