Delhi's air quality improves slightly but likely to turn 'very poor'

Pollution levels in the national capital dipped slightly on Tuesday due to favourable wind speed, but the air quality is likely to turn 'very poor' on Wednesday.

The Ministry of Earth Sciences' air quality monitor, SAFAR, stated the share of stubble burning in Delhi's PM2.5 pollution stood at 8 per cent on Tuesday and is likely to increase by Wednesday morning.

The city recorded a 24-hour average air quality index (AQI) of 223 on Tuesday. It was 244 on Monday, 254 on Sunday and 287 on Saturday. An AQI between zero 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'.

Calm winds and low temperatures allow accumulation of pollutants, while favourable wind speed help in their dispersion.

SAFAR said the AQI was likely to slip to the 'very poor' category by Wednesday due to a change in the wind direction and a reduction in the wind speed. The farm fire count around Haryana, Punjab and nearby region across the International Border was 1017 on Monday, it said.

"The boundary layer wind direction was favourable for the transport of pollutants towards Delhi. The share of stubble burning in Delhi's PM2.5 was 8 per cent on Tuesday and is likely to increase early tomorrow," it said.

It was 10 per cent on Monday, 17 per cent on Sunday and 19 per cent on Saturday.

Expecting further deterioration in air quality in the coming days, the Supreme Court-mandated Environment Pollution (Prevention and Control) Authority had on Monday asked the Uttar Pradesh and Haryana governments to be ready to close thermal power plants that do not meet the standards laid down in 2015.

Chief Minister Arvind Kejriwal on Monday requested Union Environment Minister Prakash Javadekar to hold monthly meetings with the CMs of Delhi, Punjab, Haryana and UP to curb air pollution, saying there is a lack of political will at the level of the states to address the problem of stubble burning.

The Delhi government will deploy 2,500 environment marshals across the city to generate awareness about its recently launched anti-pollution campaign, 'Red Light On, Gaadi Off' to curb vehicular pollution, according to city Environment Minister Gopal Rai.

The Ministry of Earth Sciences' Air Quality Early Warning System for Delhi said the ventilation index – a product of mixing depth and average wind speed – was 15,000 metre square per second on Tuesday and is likely to be 8,000 metre square per second on Wednesday – favourable for dispersion of pollutants.

Mixing depth is the vertical height in which pollutants are suspended in the air. It reduces on cold days with calm wind speed.

A ventilation index lower than 6,000 sqm/second, with average wind speed less than 10 kmph, is unfavourable for dispersal of pollutants.