The city's air quality turned poor on Monday as the overall air quality index (AQI) touched 206 (PM2.5) level, according to US Mission India's NowCast Air Quality Index.
An AQI between 0-50 is considered to be good, 51-100 is satisfactory, 101-200 moderate, 201-300 poor, 301-400 very poor and 401-450 severe, according to pollution control board norms.
An official of the West Bengal Pollution Control Board (WBPCB) told PTI that the city's annual average reading is 174 PM2.5 levels.
He said Monday's reading is the combined effect of wintry conditions in the air which prevents fine particulate matters hanging in the air to rise above and creates smog in late afternoon and early morning hours.
However, the Fort William air monitoring station of WBPCB recorded an AQI of 186 PM2.5 while the station at Victoria Memorial recorded 164.
"At one point of time, the AQI was 200 PM2.5 in Maidan area," environmentalist Somendra Mohan Ghosh said quoting WBPCB figures.
On Saturday and Sunday, the Fort William and Victoria Memorial stations recorded AQI ranging between 232-248 PM2.5 as smog had enveloped the air at dawn and before dusk, the WBPCB official said.
The official said the current AQI level poses health concern for individuals who have lung ailments.
"We cannot comment on the air quality reading of agencies other than WBPCB," he said.
The WBPCB said it had taken a number of measures including banning of chullahs (coal-driven ovens used by vendors), asking real estate developers to cover construction sites to prevent spray of dust particles and deploying tankers with water sprayers in the city.
Naba Dutta, the secretary of prominent green NGO Sabuj Mancha, said, "With Diwali and Kali Puja barely a week away, the air quality is likely to further worsen because of bursting of firecrackers. People are already experiencing breathing problems and there may be a rise in the number of patients with respiratory issues due to the spike in air pollution in the coming days."
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