New Delhi, Oct 13 (PTI) The national capital's air quality hit an eight-month low and was recorded just a notch shy of the “very poor” category on Tuesday, largely due to calm winds and low temperature that allowed accumulation of pollutants.
According to the Ministry of Earth Sciences' Air Quality Early Warning System for Delhi, an increase was also observed in farm fires in Punjab, Haryana and neighbouring regions of Pakistan, but its impact on the capital's air quality was marginal.
The city's air quality index (AQI) hit “very poor” levels in the morning and stood at 306 at 11 am. Thereafter, the pollution levels dipped slightly due to an improvement in the ventilation index.
The 24-hour average AQI was recorded at 300 at 4 pm, which falls in the “poor” category. The last time the air quality hit such a poor level was on February 12 when the AQI was 320.
It was 261 on Monday, 216 on Sunday and 221 on Saturday.
Dwarka Sector-8 (AQI 390) Wazirpur (AQI 372), and Mundka (AQI 352) recorded the highest pollution levels on Tuesday.
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'.
V K Soni, a senior scientist at the India Meteorological Department, said the dip in the air quality can be attributed to low wind speed which allowed accumulation of pollutants.
“The ventilation index has improved slightly and no drastic change is expected in the AQI,” he said.
Ventilation index is the speed at which pollutants can get dispersed. A ventilation index lower than 6,000 sqm/second, with average wind speed less than 10 kmph, is unfavourable for dispersion of pollutants.
PM10 levels in Delhi-NCR dropped from 300 microgram per cubic meter (µg/m3) at 9 am -- the highest this season so far -- to 293 by 5 pm µg/m3.
PM10 levels below 100 µg/m3 are considered safe in India.
PM10 is particulate matter with a diameter of 10 micrometers and is inhalable into the lungs. These particles include dust, pollen and mold spores.
The levels of PM2.5 – finer particles which can even enter the bloodstream – were 128 µg/m3. PM2.5 levels up to 60 µg/m3 are considered safe.
NASA's satellite imagery showed a large cluster of fires near Amritsar and Firozpur in Punjab and Patiala, Ambala and Kaithal in Haryana.
The System of Air Quality and Weather Forecasting and Research, SAFAR, said, “The development of strong surface-level inversion and sudden local, calm surface wind conditions led to a low ventilation coefficient and accumulation of pollutants near the surface.” Around 675 farm fires were observed on Monday around Punjab, Haryana and neighbouring border regions, but the wind direction is not favourable for transport of pollutants. Hence, only marginal contribution in Delhi's PM2.5 concentration is expected, it said.
On Tuesday, the minimum temperature was 19.8 degrees Celsius. During daytime, the maximum wind speed was 12 kmph and the direction was southeasterly, according to the IMD.
Low temperatures and stagnant winds help in accumulation of pollutants near the ground, affecting air quality.
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 percent), followed by industries (2 to 29 percent), thermal power plants (3 to 11 percent) and construction (8 percent).
This year, the Delhi government has 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 levels 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.
The government also started the spraying of “Pusa bio-decomposer” solution in non-basmati rice fields in the national capital, on Tuesday.
The solution, experts say, can turn the stubble into manure in 15 to 20 days and therefore, can prevent stubble burning.' Starting October 15, 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. PTI GVS ABH ABH