Burning eyes, choking lungs: Here’s what Delhi looks like as air pollution rises
Dense smog continued to engulf the national capital for the second day, even as temperatures dipped and air quality levels deteriorated.delhi Updated: Nov 08, 2017 13:16 IST
A thick blanket of haze hung low over Delhi for the second day on Tuesday, as air quality levels deteriorated and visibility plunged.
The Central Pollution Control Board (CPCB) identified four reasons for the sudden onset of pollution. Temperature, wind speed, relative humidity and atmospheric boundary layer had worsened Delhi’s air, CPCB experts said. Conditions are unlikely to improve over the next few days, they said.
“Meteorological conditions were such that all the local pollutants got trapped and lingered in the air. These four parameters had a direct impact on the pollution,” said D Saha, head of the air quality laboratory of CPCB.
Wednesday became the coldest of the season so far with minimum temperature at 14 degree Celsius. Tuesday was the second-coldest day of the season with the temperature dropping to 16.1 degrees Celsius.
On Monday afternoon, when temperature was around 30 degrees Celsius, PM2.5 level was just twice the permissible limit. But at 5am on Tuesday, when the temperature dropped to around 16.1 degrees, the PM2.5 level shot up by 9-10 times the permissible limit.
Another key reason for the haze in the capital is poor wind speed. While Delhi needs a minimum wind speed of 5 m/s to disperse trapped pollutants, the wind speed dropped to less than 1 m/s between 4am and 5am on Tuesday. The levels of PM2.5 were at least 10-15 times the permissible limit during this hour at stations such as DTU, Mathura Road and Delhi University’s North Campus.
“The condition was aggravated by north-westerly winds, which are bringing in smoke from the stubble burning regions of Punjab and Haryana. The south-easterly winds are helping the moisture to build up. We apprehend that similar conditions would prevail over the next two to three days,” said A Sudhakar, member secretary of CPCB.
The atmospheric boundary layer (ABL) also plays a key role in determining the level of pollution. ABL forms the ceiling within which air circulates and Air quality improves when the height of ABL is more and pollution rises when it is low.
Pollution also increases as relative humidity builds up because high moisture helps to trap air and retain more pollutants. Over the past few days, easterly winds increased the moisture in Delhi’s air. In morning hours, when humidity was at its peak, pollution shot up.
CPCB data shows humidity level was at its peak between 3am and 8am on Tuesday. During these hours, PM2.5 levels shot up by more than 10 times in almost all stations across Delhi.