Delhi breathes easier, more relief likely (Representational image)
The city heaved a sigh of relief as the pollution levels in the national capital dropped further on Wednesday. The cause of this decreasing pollution level is due to a change in wind direction. The impact of stubble burning on Delhi's air quality reduced significantly after the wind directions changed. According to IMD reports, the trend is likely to continue over the next three to four days.
At 8.45 pm, the city's overall air quality index (AQI) read 217, which falls in the "poor" category. At many places, pollution levels dropped to "moderate" category.
An AQI between 0-50 is considered 'good', 51-100 'satisfactory', 101-200 'moderate', 201-300 'poor', 301-400 'very poor' and 401-500 'severe'. An AQI above 500 falls in the severe plus category.
The levels of PM2.5 -- tiny particulate matter less than 2.5 microns in diameter that can enter the lungs and even the bloodstream -- dropped to 111 micrograms per cubic metre (ug/m3) in the Delhi-NCR region.
The PM10 concentration was 226 ug/m3 at 8.30 pm. The safe levels of PM2.5 and PM10 are 60 and 100 ug/m3, respectively. According to Kuldeep Srivastava, the head of the Regional Weather Forecasting Centre, a clear sky or absence of clouds allows sun rays to reach the earth's surface, warming up the air close to the ground which rises up and clears pollutants.
"That's what is happening over the last two days," he said. "However, a cloud cover, very light rains, and clam winds are expected on (the intervening) night of (Wednesday and Thursday), which may accelerate the accumulation of pollutants and air quality may deteriorate slightly," the India Meteorological Department official said.
The situation will improve again on Thursday due to strong winds and rains. Delhi is expected to breathe comparatively cleaner air till November 10, he said.
The Centre-run System of Air Quality and Weather Forecasting and Research (SAFAR) said, "Delhi's overall AQI has improved significantly, more rapidly than predicted, and further improvement during sunlight hours is expected."
It said a change in the wind direction led to very low biomass plume intrusion despite the farm fire count remaining very high on Tuesday.
Though Punjab recorded the season's highest farm fire count of 6,668 on Tuesday, its impact on Delhi's air quality was negligible due to a change in wind direction, SAFAR said.
It said the share of smoke from stubble burning in Delhi's PM2.5 pollution was just three per cent on Wednesday and is likely to be two per cent on Thursday.
"Western disturbances have brought cleaner air to the region. Isolated thundershowers are expected for the next two days and wind direction is likely to be southeasterly on November 7. So, no biomass intrusion," SAFAR said.
The Supreme Court-mandated Environment Pollution (Prevention and Control) Authority on Monday extended restrictions on hot mix plants, stone crushers and dirty fuel-based industries in Delhi-NCR till the morning of November 8 expecting a repeat of Sunday's episode.
The apex court had also banned construction activities in Delhi-NCR till further orders.
On Sunday, pollution level in Delhi peaked to a three-year high as high humidity due to light rains the previous day led to formation of more potent secondary particles.
Secondary particles, like include sulphates, nitrates, ozone and organic aerosols, are products of complicated atmospheric reactions between primary particles, such as particulate matter, sulphur dioxide and nitrogen dioxide directly emitted by stubble burning and vehicles, in the presence of other factors such as sunlight and moisture.
(With inputs from PTI)
