Updated: March 22, 2016 3:54:34 am
Air quality in Delhi — often called the most polluted city in the world — has improved in the last few days due to sporadic rains. According to the National Air Quality Index (AQI), on Monday at 4 pm, Anand Vihar recorded an AQI of 186, Punjabi Bagh of 139 and R K Puram of 148 — all in the moderate range.
Data from the Delhi Pollution Control Committee’s (DPCC’s) monitoring stations showed that at Punjabi Bagh, in the last 24 hours, a peak of 291 micrograms per cubic metre of particulate matter (PM) 10 was observed.
The safe limits of PM 2.5 and PM 10 — microscopic particles that enter and get embedded deep in the lung and the bloodstream — are 60 and 100 micrograms per cubic metre respectively. Last week, the levels of PM 10 had peaked at 341 micrograms per cubic metre in Punjabi Bagh, compared to a peak of 500 micrograms per cubic metre the week before. At R K Puram, the PM 10 levels peaked at 218 micrograms per cubic metre in the last 24 hours, and at 317 micrograms per cubic metre the week before that.
Air quality had been worse a week earlier, with PM 10 levels peaking at 490 micrograms per cubic metre.
Experts said in March and April, as temperatures increase after the winter months, the level of particulates falls.
“This year, thanks to two spells of rains this month, we have seen a further drop in particulate matter levels. Due to westerly disturbances seen in Afghanistan, showers have carried on for 48 to 72 hours in two spells. Humidity levels have also been high, going up to 90 per cent,” said a senior DPCC scientist.
According to data analysed by the Central Pollution Control Board (CPCB), particulate matter levels had declined in February, when compared to January.
In February, the average AQI was recorded at 293 — in the poor range — with a maximum of 372 and a minimum AQI of 186. In January, Delhi had recorded an average AQI of 362 — in the ‘very poor’ range — with maximum and minimum values at 434 and 269 respectively, according to CPCB. The month also witnessed eight days when the AQI was in the ‘severe’ category.
However, ozone levels, associated with high temperatures, remained high this month. This week, ozone levels peaked at 319 micrograms per cubic metre at Punjabi Bagh, against a one-hour safe limit of 180 micrograms per cubic metre, and an eight-hour safe limit of 100 micrograms per cubic metre.
According to experts, ozone levels go up with a rise in temperature, as the gas is formed from a photochemical reaction which needs a large amount of sunlight. The CPCB had identified ozone as of the dominant pollutant in February.
According to the National Air Quality Index’s monthly analysis report, on seven days when PM 2.5 was the dominant pollutant, ozone levels rose as well.
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