New Delhi, Oct 14 (PTI) The national capital's air quality was recorded in the 'poor' category on Wednesday, even as pollution levels dipped slightly, according to government agencies. According to the Ministry of Earth Sciences' Air Quality Early Warning System for Delhi, air quality is likely to improve to the moderate category by Thursday.
The city recorded a 24-hour air quality index (AQI) of 276. It was 300 on Tuesday. The AQI had hit 'very poor' levels on Tuesday morning and stood at 306, which was the worst since February. Thereafter, the pollution levels dipped slightly due to an improvement in the ventilation index.
Ventilation index is the speed at which pollutants can get dispersed. A ventilation index lower than 6,000 metre square per second, with average wind speed less than 10 kilometers per hour, is unfavourable for dispersion of pollutants.
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'.
Low temperatures and stagnant winds allow accumulation of pollutants near the ground, affecting air quality.
According to a senior scientist at the India Meteorological Department, the surface wind direction will be easterly and the maximum wind speed was 10 kilometers per hour on Wednesday, – which is not favourable for transport of smoke from farm fires in Haryana and Punjab.
'The ventilation index is likely to be 6,000 sqm/second on Wednesday and Thursday,' he said.
The Minister of Earth Sciences' air quality monitor, SAFAR, said 'relatively lesser stubble burning was observed' around Haryana, Punjab, and neighboring border regions on Tuesday.
The fire count was 357, but the wind direction was not favorable for transport of pollutants. Hence, only minimal contribution in Delhi's PM2.5 concentration is expected, it said.
On Wednesday, the minimum temperature was 23.7 degrees Celsius.
With Delhi-NCR bracing for months of poor air quality, experts have warned that high levels of air pollution can aggravate the COVID-19 pandemic.
Severe air pollution in Delhi is a year-round problem, which can be attributed to unfavourable meteorological conditions, farm fires in neighbouring regions and local sources of pollution.
According to an analysis by the Council on Energy, Environment and Water, a Delhi-based think tank, transportation contributes the most -- 18 to 39 percent -- to Delhi's air pollution.
Road dust is the second largest source of air pollution in the city (18 to 38 per cent), followed by industries (2 to 29 per cent), thermal power plants (3 to 11 per cent) and construction (8 per cent).
The Delhi Pollution Control Committee on Wednesday issued directions banning the use of diesel generators in the national capital from Thursday under the Graded Response Action Plan (GRAP).
The Delhi government has also launched a massive anti-air pollution campaign, 'Yuddh Pradushan Ke Viruddh', which is being led by Chief Minister Arvind Kejriwal and Environment Minister Gopal Rai.
A 'green war room' with a 10-member expert team has been set up at the Delhi Secretariat to monitor the steps being taken to deal with high level of air pollution in winters.
The Environment Department has also taken stern action against project proponents at large construction and demolition sites flouting dust control norms.
Starting Thursday, stricter measures to fight air pollution will also come into force in Delhi and its neighbourhood as part of the Graded Response Action Plan, which was first implemented in Delhi-NCR in 2017.
The measures under GRAP include increasing bus and metro services, hiking parking fees and stopping use of diesel generator sets when the air quality turns poor.
When the situation turns 'severe', GRAP recommends closure of brick kilns, stone crushers and hot mix plants, sprinkling of water, frequent mechanised cleaning of roads and maximising power generation from natural gas.
The measures to be followed in the 'emergency' situation include stopping entry of trucks in Delhi, ban on construction activities and introduction of the odd-even car rationing scheme. PTI GVS AAR AAR