The first episode of smog this year has hit Delhi and the National Capital Region, an analysis done by think tank Centre for Science and Environment showed on Wednesday. The think tank has said called it a “public health emergency”.

In a statement, the think tank said that the current smog episode has lasted for six days – the same duration during the first smog episodes of 2018 and 2020. “If conditions don’t improve, it might overtake the 2019 smog that lasted eight days,” it said.

The think tank has predicted that the smog is likely to last till Friday. “Lingering on of this year’s smog for longer duration despite relatively windier local conditions might be due to the lack of pollution control measures in the city this year,” it said.

Average intensity of the smog this year so far was 329 microgramme per cubic metre per day, the think tank said. This is lower than the 2020 smog by 7% and the one in 2019 by 3% but more intense than the 2018 one by 9%, the statement said.

At 4.30 pm on Thursday, Delhi’s air quality index, or AQI, was in the “very poor” category at 390 showed real-time data by the System of Air Quality and Weather Forecasting and Research, or Safar.

An AQI between zero and 50 is considered “good”, 51 and 100 “satisfactory”, 101 and 200 “moderate”, 201 and 300 “poor”, 301 and 400 “very poor”, and 401 and 500 “severe”.

Anumita Roychowdhury, the executive director of research and advocacy department at the think tank, said that the smog was triggered by the combined effect of unfavourable weather conditions, stubble burning and firecrackers.

The analysis by the think tank showed that the concentration of PM2.5 had crossed 250 microgramme per cubic metre – considered the breakpoint for severe AQI category – on November 4, when Diwali was celebrated. It said that the PM2.5 particles have been hovering in the sky seven days later and had reached its peak of 501 microgramme per cubic metre on November 5. It then receded to 264 microgramme per cubic metre on Tuesday.

Avikal Somvanshi, a programme manager at the think tank, said that besides the high concentration of PM2.5, the levels of other hazardous gases such as carbon monoxide and nitrogen dioxide too have remained high.

“Also, the ratio of SO2 to NO2 [sulfur dioxide to nitrogen dioxide] increased on Diwali night indicating increased pollution load from firecrackers,” Somvanshi said. “The PM2.5 concentration on Diwali night [8 pm to 8 am] has been the most intense since 2017.”

The think tank said that the 12-hour night average of PM2.5 on November 4 stood at 747 microgramme per cubic metre, 22% higher than that on Diwali night last year.

The Centre for Science and Environment conducted the analysis on real time data from air quality monitoring stations in Delhi-NCR and the Indo-Gangetic Plain. It accessed weather data from the India Meteorological Department and got the number of fires from National Aeronautics and Space Administration. Estimates of contribution of farm stubble fire smoke to Delhi’s air quality were taken from Safar.

“Even though the seasonal smog in Delhi is intense, the average daily contribution of smoke from farm stubble fires from the middle of October to November 8, 2021, has been the lowest in last four years,” Roychowdhury said. “But since November 6, its contribution has peaked to reach 48% on November 7 and it is still elevated.”

She added: “This [the smog] requires urgent emergency action on key combustion sources [vehicles, industry, waste burning] and dust sources [construction and roads] to prevent further trapping of pollution when there is no wind to blow this away. We need pollution-source-wise and hotspot-wise status of action.”

Delhi launches campaign against open burning of waste

Meanwhile, Delhi Environment Minister Gopal Rai on Thursday began a month-long campaign against open burning of waste and biomass, reported PTI.

“We have launched a campaign to prevent open burning of waste and biomass to cut down on pollution generated within Delhi,” he told reporters.

Rai inspected the Ghazipur landfill and directed East Delhi Municipal Corporation officials to prepare a fire control plan there. He said that 550 patrol teams have been formed, of which 246 will be deployed at night.