Delhi's air quality index (AQI) remained in "severe" zone on Thursday, November 5, as the national capital continued to be shrouded in a thick layer of haze that lingered over it and its suburbs.
The raging farm fires (stubble burning), falling wind speed, and low temperatures pushed the union territory's air quality to the worst levels in around a year.
Several people also complained of watery eyes, and itchy throats as Delhi's skies hung heavy and acrid over the region. According to experts, adverse meteorological conditions - low temperatures calm winds - and smoke from stubble burning in neighbouring states resulted in a dense layer of haze shrouding Delhi's skies on Wednesday night as the national capital's air quality index entered the "severe" zone.
PM10 levels in Delhi-NCR stood at 561 microgram per cubic meter (ug/m3) -- the highest since November 15 last year, when it was 637 ug/m3, according to CPCB data. PM10 levels below 100 ug/m3 are considered safe in India. PM10 is particulate matter with a diameter of 10 micrometers which is inhalable. These particles include dust, pollen and mold spores.
The levels of PM2, finer particles which can even enter the bloodstream, were 347 ug/m3. PM2.5 levels up to 60 ug/m3 are considered safe.
On Wednesday evening, the noxious haze reduced visibility to merely 600 metres at the Safdarjung Observatory, smudging landmarks from view. It was 1,200 metres on Thursday morning.
If this was not enough, a large number of people across Delhi-NCR burst firecrackers to mark the festival of Karwa Chauth.
According to the Indian Meteorological Department (IMD), the maximum wind speed was 5 kilometres per hour on Thursday morning and the minimum temperature was 11.2 degrees Celsius. Calm winds and low temperatures trap pollutants close to the ground, while favourable wind speed helps in their dispersion.
Health experts are of the view that during the COVID-19 pandemic, air pollution has become a serious health concern for about the two crore residents of the national capital.
According to a doctor at Sir Ganga Ram Hospital, intake of every 22 micrograms per cubic metre of polluted air is equivalent to smoking a cigarette.
Ajit Jain, the nodal officer for COVID-19 at Rajiv Gandhi Super Specialty Hospital, told PTI that air pollution was turning the pandemic catastrophic.
IMD officials said sudden change in the wind pattern led to "subsidence" -- the downward movement of air over a large area as it cools and becomes heavier.
"The wind speed slowed down suddenly after 10 am in the Delhi-NCR region. The temperature has dipped alarmingly over the last few days," V K Soni, head of IMD's environment monitoring research centre, told the agency.
The haze was primarily smoke from stubble burning in Punjab and Haryana. Unfavourable meteorological conditions trapped it in Delhi-NCR," he added.
Delhi recorded an Air Quality Index (AQI) of 461 at 8 am. It was 279 at 10 am on Wednesday. All the 36 monitoring stations recorded the air quality in the ''severe'' category.
The neighbouring cities of Faridabad (431), Ghaziabad (484), Greater Noida (463), Gurugram (440) and Noida (461) also recorded ''severe'' levels of air pollution.
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".
Stubble burning accounted for 40 per cent of Delhi's pollution on Sunday, the maximum so far this season.
(With inputs from PTI.)