The air quality of Delhi improved to ‘poor’ category on Wednesday, mainly due to a shift in the direction of the wind.
The air quality is expected to improve to ‘moderate’ or lower end of ‘poor’ category on Thursday, but may deteriorate slightly on Friday due to a change in wind direction, said government-run monitoring agency SAFAR (System of Air Quality and Weather Forecasting and Research).
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Isolated thundershower forecast over the next two days may also reduce pollution.
The Air Quality Index (AQI) of the city on Wednesday was 214 (poor); on Tuesday it was 324 (very poor); it was 407 (severe) on Monday, according to the 4 p.m. bulletin by the Central Pollution Control Board (CPCB), which is the average of the past 24 hours.
The contribution of stubble burning in neighbouring States to Delhi’s air pollution was only 3% on Wednesday, and is expected to be 2% on Thursday, according to SAFAR. The contribution of stubble burning was as high as 44% earlier this season.
According to SAFAR, there were 5,300 farm fires in Punjab and Haryana on Tuesday, the highest this season. “The change in wind direction, however, led to very low biomass plume intrusion [into Delhi] despite the fact that fire count observed on Tuesday was very high,” it said.
The wind direction is currently south-south westerly, leading to less transfer of smoke from stubble burning into Delhi, while north-westerly winds bring in plume from Haryana and Punjab into the city.
“Improvement in AQI is expected on Thursday... by November 8, shift in wind direction back to north westerly is expected and AQI is likely to shift to ‘poor’ or ‘very poor’,” SAFAR stated.
‘Stubble into CNG’
On Wednesday, Chief Minister Arvind Kejriwal said on Twitter that technology is available to convert stubble into CNG. “I had several meetings with experts on Wednesday. It is technologically and commercially possible to convert stubble into CNG. This will provide jobs, additional income to farmers and solve our annual problem of pollution. However, it requires all governments to come together and work on this,” he tweeted.
PTI adds:
The Supreme Court-mandated Environment Pollution (Prevention and Control) Authority had on Monday extended the 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 Supreme 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 on Saturday led to the formation of more potent secondary particles.
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Secondary particles are a product 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.
Examples of secondary particles include sulphates, nitrates, ozone and organic aerosols.
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.
