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Opinion

Delhi’s air quality is approaching the ‘severe’ zone

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Delhi’s air quality was at the upper end of the “very poor” category on Wednesday morning, while pollution levels have already entered the “severe” zone in the neighboring cities of Ghaziabad and Greater Noida.

The city’s Air Quality Index (AQI) was 381 at 9 am. The 24-hour average was 367 on Tuesday. It was 318 on Monday and 268 on Sunday.

Ghaziabad and Greater Noida recorded an AQI of 430 and 410, respectively. 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”.

The maximum wind speed is expected to be 12 km / h on Wednesday, according to the Indian Meteorological Department (IMD).

The low temperature was 8.2 degrees Celsius on Wednesday and the maximum is expected to settle around 27 degrees Celsius, the meteorological department said.

The low temperature this season has remained 2-3 degrees Celsius below normal in the absence of cloud cover most days, according to IMD officials.

Clouds trap some of the outgoing infrared radiation and radiate it downward, heating the ground.

The predominant wind direction was west-northwest most of the days. These winds blow from the snow-covered western Himalayas onto the plains.

Read also | Delhi AQI rises to 339, remains in very poor area

Another reason for the below-normal temperatures is La Niña, a phenomenon associated with cooling Pacific waters and an antithesis to El Niño. Calm winds and low temperatures trap pollutants close to the ground, while favorable wind speeds help disperse them. The central government’s Air Quality Early Warning System for Delhi said air quality is likely to remain at the upper end of the “very poor” category due to unfavorable weather conditions.

There is a possibility that air quality will reach the “severe” category between December 4-7, he said.

The city’s ventilation rate, a product of mixing depth and average wind speed, was 2,500 m2 / s on Tuesday and is likely to be 6,000 m2 / s on Wednesday.

Mixing depth is the vertical height at which contaminants are suspended in the air. Reduce on cold days with calm wind speeds.

A ventilation rate of less than 6,000 m2 / second, with an average wind speed of less than 10 km / h, is unfavorable for the dispersion of pollutants.

The contribution of stubble burning in neighboring states to Delhi’s PM 2.5 levels was 4 percent on Tuesday, 7 percent on Monday and 6 percent on Sunday, according to the Ministry’s air quality monitor. of Sciences of the Earth, SAFAR.

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