Air quality falls as winds calm down

While the farm fires in neighbouring states of Haryana and Punjab have drastically reduced -- it contributed just 4% to Delhi’s PM 2.5 levels on Tuesday, according

While the farm fires in neighbouring states of Haryana and Punjab have drastically reduced -- it contributed just 4% to Delhi’s PM 2.5 levels on Tuesday, according to System for Air Quality and Weather Forecasting and Research -- the national capital’s air quality plunged further to the upper end of the “very poor” zone of the air quality index (AQI) on Tuesday.

HT Image

According to government agencies, it is likely to remain there throughout the week owing to the wind speed calming down and wind patterns changing in the coming days.

As per the Central Pollution Control Board (CPCB), the AQI on Tuesday was 367, even worse than Monday’s 318, though both are in the very poor category. On a scale of 0 to 500, an AQI value between 300 and 400 is considered very poor, and those above 400 are considered severe.

The air quality levels continued to deteriorate further on Tuesday evening, with most of the hotspots slipping into the ‘severe’ zone. By 9 pm, 11 of the 35 monitoring stations recorded ‘severe’ air quality including --- Anand Vihar (414), Ashok vihar (437), Bawana (413), DTU (409), Jahangirpuri (443), Mundka (413), Nehru Nagar (404), Patparganj (410), Punjabi bagh (405), Rohini (414) and Vivek Vihar (425).

Delhi had last seen average air quality levels in the ‘severe’ zone on November 25 with an AQI reading of 413. After this air quality had improved to ‘poor’ and even recorded a ‘moderate’ air quality day on November 27, but it started deteriorating again from Monday onwards with the AQI plunging to ‘very poor’. This November saw nine ‘severe’ air quality days.

According to experts, every year, after the peak pollution in November, which is mostly attributed to stubble burning, bad air episodes are seen towards end-December and early January. This is mainly because meteorological conditions are least favourable during that time, while the baseline pollution (local emissions) stays the same.

According to scientists at the India Meteorological Department (IMD), the average wind speed during the day reduced to 7-8 kmph from 10-12 kmph on Monday. “The wind speed will further reduce from December 4 or 5 and the direction is likely to change to easterly, from the present north-westerly. The change in direction is due to a western disturbance that will affect Jammu and Kashmir and Himachal Pradesh from the night of December 3, which will also have an impact on Delhi. Whenever there is a change in wind pattern, winds turn calm and trap pollutants,” said Kuldeep Srivastava, head of IMD’s regional weather forecasting centre.

He said easterly winds are also likely to bring in moisture, which when combined with calm winds allow pollutants to accumulate. There is also a forecast of shallow fog on December 4 or 5. “Besides, the change in wind pattern will also lead to a rise in minimum temperature between December 4 and 7, when it is likely to remain around 10-12 degrees Celsius. Thereafter, north-westerly winds are likely to return resulting in a drop in temperature,” Srivastava further said.

On Tuesday, the Safdarjung Observatory --- the official marker for the city’s weather --- recorded a minimum temperature of 8.1 degrees Celsius, two notches below normal. The maximum settled at 27.2 degrees Celsius, two notches above normal.

Sagnik Dey, associate professor, IIT-Delhi, said, “In October and November, farm fires contribute about 25% to the overall pollution in Delhi. In December, we record the same pollution level even without stubble burning because of reduced dispersion of pollutants. This year, while a large section is still working from home, the benefit derived from reduced work-related travel was lost to low use/frequency of public transport,” Dey said.

Anumita Roychowdhury, executive director, Centre for Science and Environment (CSE), said at present, the only factors at play are meteorological and local pollutants. “Even though there has been a declining trend in the overall pollution levels since 2017, Delhi still has to reduce its PM 2.5 concentrations at least by 60% to mitigate these peak episodes and meet the clean air standards. Also, on-ground monitoring of waste burning and emissions from illegal industries need to be stepped up to have some real impact. If we are able to achieve all that, air quality may not touch ”severe” during December and January,” she said.

The CPCB, which is now officially in charge of implementing the Graded Response Action Plan (Grap) --- to combat different levels of air pollution --- in Delhi-NCR, is taking day to day measures to keep local pollution levels under control.

“We are monitoring the situation closely. Measures under the ‘very poor’ zone are already being enforced. Patrolling teams are carrying field inspections regularly,” said a senior CPCB official, who did not wish to be named.

Meanwhile, despite repeated attempts, MM Kutty, chairperson of the Commission for Air Quality Management (CAQM) in NCR and adjoining areas, could not be reached for a comment.