Air turns unbreathable as pollution season sets in

Delhi's air quality index (AQI) has reached the "very poor" level for the first time this season due to low temperatures, calm winds, and rising farm fires in neighboring states. Experts warn that the AQI is likely to remain "very poor" until at least Wednesday. Of the 36 air stations in Delhi, 24 had readings in the "very poor" zone, while two were in the "severe" zone. Farm fires in Punjab and Haryana are also contributing to the spike in pollution levels.

The annual onslaught of pollution appears to have gripped Delhi again as the air quality index (AQI) jumped to the “very poor” level for the first time this season on Sunday, aided by a combination of factors which included low temperature, calm winds, and local as well as external sources of pollution which included rising farm fires in northern states, officials said.

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Delhi clocked an AQI of 313 on Sunday, according to the Central Pollution Control Board’s (CPCB) bulletin — a sizeable rise from Saturday’s AQI reading of 248 (poor). This is also the first time in more than five months that Delhi’s AQI was “very poor”, with it last recorded in this category on May 17, when the AQI was 336 due to dusty winds coming in from Rajasthan.

Forecasts show there is likely to be no significant change in meteorological conditions in the next few days, which will mean that Delhi’s AQI will likely remain “very poor” till at least Wednesday, experts warned. Farm fires in upwind states of Punjab and Haryana too are likely to begin impacting the air quality more severely, they added.

Of the 36 air stations in Delhi that published readings on Sunday, 24 had readings in the “very poor” zone (301-400), according to CPCB’s Sameer app. Two — Ashok Vihar and Aya Nagar — were even in the “severe” zone (401-500), while the remaining 10 were “poor”.

The CPCB classifies an AQI between 0-50 as “good”, between 51 and 100 as “satisfactory”, between 101 and 200 as “moderate”, between 201 and 300 as “poor”, between 301 and 400 as “very poor”, and over 400 as “severe”.

One of the primary reasons for the abrupt spike in pollution levels, experts said, was a recent jump in farm fires in northern states. On Saturday, there were a total of 265 farm fires reported in Punjab and Haryana — the most in a single day so far this season — according to satellite data from National Aeronautics and Space Administration (Nasa) accessed by HT. On Friday, there were 206 such fires, data shows. In the week preceding that, there were an average of 90 such blazes every day.

To be sure, farm fires this season have not yet seen a spike that they generally do this time of the year. In October, there have been 2,436 reported farm fires this year in the two states, according to Nasa’s satellite data. This is 75% fewer than the 2012-2022 average of 9,775 such blazes reported in the same time period.

VK Sehgal, professor and principal scientist at IARI and part of the Consortium for Research on Agroecosystem Monitoring and Modelling from Space (CREAMS) said this year, fires had started earlier than last year, but the count is yet to spike significantly. “Initially, numbers were higher than 2022, but that was because the harvesting was delayed last year due to rains in early October. Numbers tend to spike significantly by the end of October and in the first week of November, and if we still don’t see a significant jump, then the worst would be over,” he said.

Data from the Decision Support System (DSS), part of the ministry of earth sciences, estimated the contribution of biomass burning to be around 16.4% on Sunday, with it forecast to rise to around 30.6% on Monday and around 32.8% by Tuesday. With meteorological conditions projected to remain the same — persisting lack of strong winds will trap local sources of pollutants, the smoke is certain to create the air significantly more toxic.

Among local emissions, the transport sector’s contribution was said to be the highest — at 15.2% on Sunday. This could rise further, to 16.1% on Monday, before dipping to 13.6% on Tuesday. DSS data showed only around 27.8% of Sunday’s PM 2.5 concentration had its source in Delhi, with the remaining coming from biomass burning and trans-boundary pollution.

Low temperature and calm winds at night has led to accumulation of pollutants in the region. Delhi’s minimum temperature continued to dip, falling to the season’s lowest of 15.6 degrees Celsius on Sunday — three degrees below normal. It was 15.8°C a day earlier.

India Meteorological Department (IMD) scientists Kuldeep Srivastava said wind speeds remained calm in the early hours of the day and were below 5 km/hr till around 2.30pm. “We saw haziness through the day and visibility was down to around 1500-1800 metres during the day. Normally, it is over 4,000 metres,” he said, adding that wind direction was also pre-dominantly northwesterly, which carries pollutants from farm fires to the capital.

“No significant change in the meteorological conditions is expected in the next few days,” he added.

Srivastava said even though a feeble western disturbance was already influencing northwest India, its impact will be over by Monday. “No western disturbance is expected in the next seven days then,” he said.

Dipankar Saha, former head of CPCB’s air laboratory, said this trend in deterioration was consistent with the last few years. “This both a combination of meteorology and the geological disadvantages Delhi has. As temperatures dip further, calm winds at night will become more common. The mixing height will dip too, so escaping very poor air is unlikely, unless strong winds blow,” said Saha, adding that over the last few years, the number of severe air days was reducing.

A day earlier, the Commission for Air Quality Management (CAQM) in NCR had invoked measures under Stage-II or the ‘very poor’ category of the Graded Response Action Plan (GRAP), in anticipation of this deterioration. The measures under this category include strict enforcement of the ban on DG sets, ensuring an uninterrupted power supply across NCR, enhancing parking feed to discourage the use of public transport and augmenting bus and metro services by inducting additional fleet, among others.

With data inputs from Abhishek Jha