Air quality in the city hit a three-week low on Friday, touching a reading of 260 (poor) on the Central Pollution Control Board’s (CPCB) Air Quality Index (AQI) bulletin.

The concentration of PM2.5 (finer particulate matter) pollutants stood at an average of 290ug/m3, almost five times the safe limit, but were as high as 350ug/m3 at 7pm in the vicinity of Vikas Sadan, where the Haryana State Pollution Control Board operates an air quality monitor.

This is the worst that air quality in the city has been since April 5 when the AQI reading stood at 280 (poor).

Since then, the city’s air has lingered mostly in the ‘moderate’ or ‘poor’ category, and was in the ‘good’ category for two days after it rained on April 16 and 17.

Experts and officials said that rising temperatures and strong wind speeds were to blame for this present deterioration.

“It is common knowledge that air quality during the summer is better due to rising temperatures, but this is not entirely true,” Guneet Singh, who heads a city-based non-profit that works in the field of air pollution, said. Singh explained that rising mercury causes hot air to climb, carrying pollutant particles with it to higher “mixing heights” in the atmosphere, which is a positive outcome of the summer.

On the other hand, rising temperatures also lead to high wind speeds.

“As hot air rises, it creates imbalances of pressure in the atmosphere close to the earth, and winds begin rushing from high to low pressure zones. In case of Gurugram and the NCR, such winds come from Rajasthan, carrying with them with lots of dust, and worsening the quality of ambient air,” Singh said.

City air on Friday was also the worst in Delhi-NCR, as per the CPCB’s AQI bulletin. Delhi stood at 215 (poor), while Faridabad stood at 186 (moderate). Ghaziabad and Noida were at 259 (poor) and 232 (poor) respectively.

First Published: Apr 27, 2019 00:00 IST