The clean rain-washed skies in the national capital might soon be filled with smoke and pollutants over the next week, giving way to the annual air emergency in the city.
With multiple factors likely to coincide - intensified stubble burning activity, onset of winter and festive season - Delhi, this year, may be staring at a short and severe bad air episode, said scientists and government officials tracking the pollution situation in Delhi-NCR.
Even though this is the cleanest October in Delhi since 2019, with only two 'poor' days recorded so far, the change in weather and wind pattern from October 20 coupled with intensified farm fires are most likely to lead to deterioration in air quality, said officials in the Delhi government’s environment department.
On Sunday, state environment minister Gopal Rai said that Delhi's air quality has started deteriorating because of a spike in farm fire instances in neighbouring Punjab and Haryana. To combat the annual spike in pollution levels, the Delhi government has launched its winter action plan that focuses on 10 major problem areas, including dust emissions, waste burning and fast redressal of pollution-related complaints.
As per data maintained by the Central Pollution Control Board (CPCB), Delhi saw the first poor day this month on October 16 with an air quality index (AQI) reading of 284. On Sunday, the AQI was 298, though in the 'poor' category, but reaching close to 'very poor'.
An AQI reading between 201 and 300 is considered 'poor'; 301-400 ‘very poor’, while 401 and above is 'severe'. Data also shows that in the past three years, by this time of the year there would be more ‘poor’ days and even a ‘very poor’ day reading as well.
In 2020, 10 'poor' days were recorded during October 1-17 with one 'very poor' day reading. In 2019, there were seven 'poor' days with one 'very poor' day recorded in the same period.
Beginning of the decline
According to senior officials in the environment department, next two weeks are crucial. "We are watching the situation closely and once the rain and wind pattern change, AQI levels are likely to shoot up. The rains and winds bought us time."
"Delhi has already recorded two 'poor' air days when the rain just happened, which will clean up the air for a few days. As per inputs received from the weather department, with a change in wind pattern from October 19, rain will recede and winds could slow down. A dip in night temperature is also expected from October 21," the official said.
The change in weather conditions and the return of northwesterly winds will again bring smoke and pollutants from the crop stubble burning in Punjab, Haryana and Pakistan. "This year, a delayed monsoon withdrawal and delayed rains post-withdrawal have delayed stubble burning and hence many farmers are yet to clear their fields of paddy stubble. This has reduced the window between clearing fields and sowing the next crop, which means the burning will only get more intense. We have been monitoring satellite data of farm fires to assess the situation back home," the official added.
Farm fires leading to a spike
Satellite images from the National Aeronautics and Space Administration (NASA) fire tracker showed a spike in the number of ‘red dots’ that indicate farm fires in Punjab and Haryana and a ring of smoke being transported to the northwest region, including Delhi.
"The first clear visible signs of smoke transport to Delhi and beyond because of significant increase in fire activities in Punjab, Haryana and Pakistan over last few days. The extended regional view of the satellite images shows a ring of smoke being transported over the northwest Indian sub-continent," said Pawan Gupta, a research scientist at the Goddard Earth Sciences Technology and Research (GESTAR), Universities Space Research Association (USRA).
The Union Ministry of Earth Sciences (MoES) early warning system for air pollution shows a spike in the farm fire counts on October 16.
"The contribution of smoke from farm fires to overall Delhi pollution was 14 per cent on Saturday, which with rain on Sunday fell to 2 per cent. The effect of rain will soon wash out and intensified burning will most likely push air quality in the 'very poor' zone," the bulletin on Sunday said.
It also said that the lead pollutant in the air was PM 2.5 that is mainly generated from burnt smoke and vehicular emissions.
Experts also said that the next two weeks are crucial for Delhi. The small window with intense burning activity combined with low wind speed and a dip in temperature may coincide with Diwali (with the bursting of firecrackers despite a blanket ban in place) falling early this year on November 4, which may result in a short and severe smog episode.
A recent analysis by Delhi Pollution Control Committee (DPCC), based on PM 2.5, the average concentration values shows that November 1-15 is when AQI dips to 'severe' category. "The number of farm fire counts has been on a rise over the past week. The numbers in Punjab are lower than last year, but what is notable is that the intensity will increase sharply because of the window for clearing and sowing getting shorter. In a short duration, there may be peak burning activity, which when combined with other factors and local pollution sources, may cause a steep spike in pollution levels," said Sagnik Dey, associate professor, Centre for Atmospheric Sciences, IIT-D.
Weather forecasters add that the change in wind direction and drop in temperature will come into play at the same time when burning will be at its peak, allowing smoke particles to stick close to the earth’s surface.
Mahesh Palawat, vice-president, Skymet, a private weather forecaster said: "When the wind direction is transitioning, the speeds reduce drastically and this leads to an accumulation of pollutants already present in the air. The winds, now easterly, will change to north-westerly from October 19 onwards. The respite might be short as pollution levels are likely to rise again from October 19 itself."