Rain, stronger winds help clean up Delhi's air, AQI in 'moderate' category

The air quality in the national capital improved significantly on Tuesday as rainfall, along with stronger winds, helped clean up pollutants, authorities said.

According to Central Pollution Control Board's mobile application SAMEER, the air quality index (AQI) was recorded in 'moderate' category at 171 in the evening, while it was 168 in the morning, much better than the city's AQI on Monday which stood at 221 in 'poor' category.

The city's 24-hour average AQI was 435 on Sunday and 414 on Saturday (Diwali).

An AQI between 0 and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.

According to the Ministry of Earth Sciences' air quality monitor SAFAR, the overall air quality of Delhi was in the moderate category as of Tuesday morning.

"Surface winds are west-southwesterly and energetic, very favourable for pollutant dispersion. Rainfall along with stronger winds under the influence of Western disturbance helped to clean the build-up of pollution in the Indo Gangetic Plain,” it said.

It also said that effective stubble fire counts with sufficient potential estimated from SAFAR-multi-satellite products are significantly reduced and are around 98.

"Boundary layer wind direction is north-northwesterly, however, since the fire-related emissions have significantly reduced, a significant impact is not expected. Stubble burning share in PM2.5 in Delhi's air is almost negligible and estimated at a marginal three per cent for today,” SAFAR said.

It, however, said that the significant AQI improvement is short-lived.

The AQI is likely to marginally deteriorate to the 'poor' category on Wednesday.

"AQI is forecasted to further deteriorate to the higher end of the 'poor' to lower end of the 'very poor' category on 19th and 20th November,” it said.

In Delhi-NCR, the levels of PM2.5 -- which is about three per cent the diameter of a human hair and can lead to premature deaths from heart and lung diseases -- were 73.7 microgram per cubic meter (µg/m3) at 5 pm. The safe limit is 60 µg/m3.

PM10 level stood at 130 µg/m3 at 5 pm. PM10 levels below 100 µg/m3 are considered safe in India and 500 µg/m3 is the emergency threshold.

The neighbouring cities of Faridabad (172), Ghaziabad (166), Greater Noida (186), and Noida (178) recorded their AQI in “moderate” category. They recorded 'poor' AQI on Monday and braved “severe” air quality on Saturday and Sunday.

Gurugram's AQI improved marginally but remained in the 'poor' category at 204. It was 246 on Monday.

Delhi had recorded the worst pollution levels on Diwali in the last four years due to the combined effect of stubble burning, firecrackers and unfavourable meteorological conditions.

The air quality on the day after Diwali was also the poorest since 2016.

In a special report released on Sunday, the Central Pollution Control Board had said that almost all pollutants reported higher values on Diwali this year as compared to 2019.

It could be attributed to bursting of firecrackers, higher share of stubble burning and unfavourable meteorology during the festival season, the CPCB had said.