As rain goes away, Delhi pollution starts rising ahead of Diwali season
The air quality has started to worsen in the national capital region with levels of particulate matter surpassing safe limits on Friday — barely three days after the last of the monsoon rains— heralding the beginning of a period of pollution that stretches well into winters and is regarded a public health hazard.
The spike mainly was in the levels of PM10 – dust particles roughly a fifth of the diameter of an average human hair. On Tuesday, at around 1pm, the concentration of PM10 in air was recorded at 35ug/m3. By 8pm on Friday, it had crossed 222ug/m3, exceeding the safe limit of 100ug/m3.
The air quality in Delhi is generally the best during the monsoons when rains help settle local dust and strong winds prevent accumulation.
In the past 48 hours, weather experts have said, the wind patterns have changed.
“This happens during this time of the year when the weather transitions from monsoon to winter. The wind becomes calmer and moisture declines. Loose soil on the surface is getting suspended in the air but is not getting dispersed. As a result local pollution is building up,” said D Saha, former head of the CPCB’s air quality laboratory.
The wind speed at 5.30pm on Friday in Delhi had dropped to almost 0kmph, which meteorologists term as ‘calm wind’. The minimum relative humidity dropped from 71% on Monday to 53% on Friday. On Friday, the overall air quality index (AQI) of 198 was on the cusp of ‘poor’ category that begins from 201. “While the overall AQI value on Wednesday was 88, on Friday it was recorded to be 198. The AQI value on Monday, the day Delhi received its last monsoon rain, was 52,” said a senior official of the Central Pollution Control Board’s air quality laboratory.
The AQI is a measure of PM10 and smaller PM2.5 particles, as well as concentration of gases such as carbon monoxide and nitrous oxides. ‘Poor’ is the third lowest of six grades classifying air pollution.
In November last year, the air remained in the worst ‘severe’ category for nearly a fortnight, enveloping the region in a thick haze and forcing authorities to order the closure of schools as young children and elderly were advised to avoid going outdoors.
“The AQI at present is still better than what it was in 2016 and 2017 during this time of the year. Last year the air quality had turned poor by this time as the AQI had crossed the 200 mark,” said a scientist of the Delhi Pollution Control Committee. The withdrawal of monsoon is expected to be announced in less than a week. The announcement is done after several meteorological conditions are fulfilled – one among which is a dry spell lasting at least five days.
“We are expecting monsoon would start its withdrawal within the next 48 hours from west Rajasthan. It is expected to withdraw from Delhi in less than a week’s time,” said BP Yadav, deputy director general of the Met department.