Delhi's AQI close to 'severe plus'; odd-even rule may be imposed soon

Delhi's air quality has deteriorated further and now stands close to the "severe plus" category. On Friday morning, the national capital's air quality index (AQI) was 437, according to the Central Pollution Control Board (CPCB). An AQI higher than 450 falls under the category "severe-plus".

If Delhi slips into the "severe plus" category, the government is likely to implement the odd-even car rationing measure. The AQI declined from 419 at 4 pm on Thursday.

The capital's 24-hour average AQI, recorded at 4 pm every day, was 401 on Wednesday, 397 on Tuesday, 358 on Monday, 218 on Sunday, 220 on Saturday, and 279 on Friday.

The relatively better air quality last weekend is attributed to rain. Air pollution levels surged in the following days due to intense firecrackers bursting on Diwali night and a resurgence in stubble burning in the neighbouring states.

These effects were compounded by unfavourable meteorological conditions, primarily calm winds and low temperatures, hindering the dispersion of pollutants. Neighbouring Ghaziabad (374), Gurugram (404), Greater Noida (313), Noida (366), and Faridabad (415) also recorded very poor to severe air quality.

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", 401 and 450 "severe", and above 450 "severe-plus".

Odd-even scheme in Delhi soon?

Earlier this week, Delhi environment minister Gopal Rai mentioned the possibility of the return of the odd-even car rationing measure if the AQI crosses the 450 mark. The measure, implemented four times since 2016, allows cars to operate on alternate days based on the odd or even last digit of their registration numbers. The last enforcement was in 2019.

The Delhi government last week postponed its implementation after a notable improvement in the city's air quality due to rain on Friday.

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Recent findings from a joint project by the Delhi government and IIT-Kanpur found that vehicular emissions accounted for about 38 per cent of the capital's air pollution on Wednesday. This was reduced to 25 per cent on Thursday.

Secondary inorganic aerosols -- particles such as sulfate and nitrate that are formed in the atmosphere due to the interaction of gases and particulate pollutants from sources like power plants, refineries, and vehicles -- are the second major contributor to Delhi's foul air, accounting for 30 to 35 per cent of the air pollution in the city the last few days.

On Thursday, the Delhi government set up a six-member special task force to ensure strict implementation of measures outlined in the Grap in the capital. Delhi's special secretary (environment) will head the STF, whose members include senior officials from the departments of transport, traffic, revenue, Municipal Corporation of Delhi and Public Works Department.

Will air pollution in Delhi subside soon?

Calm winds and low temperatures are allowing accumulation of pollutants, and relief is unlikely over the next few days, an official at the India Meteorological Department (IMD) said. An improvement in the wind speed from November 21 onwards might bring air pollution levels down, he said.

Delhi's air quality dropped over the last few days despite the state government implementing stringent measures, including a ban on construction work and the entry of diesel-guzzling trucks into the city.

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According to IQAir, a Swiss company that specialises in air quality monitoring, Delhi was the most polluted city in the world on Thursday, followed by Baghdad and Lahore. According to a report compiled by the Energy Policy Institute at the University of Chicago (EPIC) in August, air pollution is shortening lives by almost 12 years in Delhi.

An official of the Commission for Air Quality Management (CAQM) had earlier said stringent measures, including a ban on construction work and the entry of polluting trucks in the national capital, under the final stage of the central government's air pollution control plan called the Graded Response Action Plan (Grap) will continue until further orders.

(With agency inputs)