Air back in ‘very poor’ zone as wind speed slows down

Delhi's air quality deteriorated further with the AQI surpassing the "very poor" mark of 300. Weakening winds and a change in wind direction are the main causes, and improvement is not expected until after October 31. Satellite cities had better air quality, but Delhi and the larger NCR are in a period of poor air quality. Farm fires are a major contributor, but this year's instances are lower than previous years. However, officials warn that the number of fires may still increase. The change in wind will also affect temperatures in Delhi.

Delhi’s air quality index (AQI) surpassed the “very poor” mark of 300 on Saturday, a significant deterioration from the 261 (poor) recorded a day earlier. Experts said a weakening of winds over the region was behind the jump air pollution and any improvement can only be expected after October 31 (Tuesday).

People at the Kartavya Path as a haze shrouds the India Gate on Saturday. (Arvind Yadav/HT Photo)

Northwesterly winds have temporarily been replaced with those from the southeast, which are weaker and are thus leading to dust, industrial emissions and tailpipe gases to be trapped closer to the ground.

“The winds are calm at night due to which dispersion of pollutants is poor and we see a dip in air quality,” said India Meteorological Department (IMD) scientist Kuldeep Srivastava.

According to the 4pm bulletin of the Central Pollution Control Board (CPCB), some of Delhi’s satellite cities had better air quality: AQI was 291 in Ghaziabad, 252 in Gurugram, 272 in Faridabad and 286 in Noida.

Delhi and the larger national capital region (NCR) covering these areas are in the middle of a sensitive window when air quality typically plummets to levels unfit for breathing in. A large contributor to that problem is smoke from farm fires in Punjab and Haryana, where farmers tend to burn the stubble left after paddy cultivation as an inexpensive and quick method to clear their fields.

Mahesh Palawat, director at Skymet, a private weather forecasting agency, said various factors including local pollution, paddy stubble burning, and calm wind conditions were behind the deterioration in air quality. “Stubble burning has started and contributes towards pollution. Moreover, winds are low due to which the dispersion of pollutants is poor. Local pollution is also prevalent. We don’t see any improvement in the wind speed or air pollution in the next few days,” said Palawat.

Data analysed by HT offer some, although early, signs of hope. According to real-time recording of fires by Nasa’s Fire Information for Resource Management System (FIRMS), Punjab and Haryana have recorded 3,669 possible stubble burning instances --- far lower than the 8,239 recorded last year and the 7,049 recorded the year before.

The number of farm fires seen this year between October 1 and 25, and in the last week, ranks the lowest among the last 11 years when the same time frames are considered.

Punjab Pollution Control Board chairman Adarshpal Vig said the number of farm fires are lower than last year because of a conscious choice and farmers are cooperating with the government in attempts to reduce the practice.

“Except the three districts, rest of Punjab has seen a downward trend of farm fires. Last year a total 2067 cases were reported on October 28, while it was just 127 this year. This is a very optimistic trend,” said the PPCB chairman.

But officials said that trend may be too early and the number of fires will increase in coming days particularly in areas where farmer unions have a strong support base.

In Delhi, the change in wind will also affect temperatures.

According to the IMD’s weekly forecast, the maximum temperature is expected to hover around 33°C on Sunday, while the minimum temperature is expected to stay around 16°C – slightly higher than what they have been of late.

“We are seeing some clouding due to a western disturbance. When there is a cloud cover, radiation released after sunset is trapped by the clouds. This leads to a slight increase in temperature due to which temperature may rise,” said Palawat.

As per the Early Warning System (EWS) for Delhi-NCR developed by the Indian Institute of Tropical Meteorology that the Commission for Air Quality Management (CAQM) relies on for its forecasts, the air quality is likely to remain in the very poor category till October 31.

(With inputs from HTC in Chandigarh)