NEW DELHI: Even with just three “good” air days, August has been the cleanest month in terms of air quality since Central Pollution Control Board (CPCB) has launched Air Quality Index (AQI) in April 2015.

Overall, 2020 has also been the cleanest year with the maximum number of “good” air days. Air quality is considered “good” when AQI is at 50 and below. Delhi has already recorded four “good” air days this year — compared to two last year and none in 2018.
According to the CPCB data, the highest AQI recorded this month was 87 on August 8, with no “moderate” day — between 101 and 200 — recorded so far. At 63, the average AQI this month has been “satisfactory”, when air quality oscillates between 51 and 100. “Delhi only recorded ‘satisfactory’ and ‘good’ air days this month. We may well see a few more days of ‘good’ air this year,” said a CPCB official.
In 2015, when AQI was launched, Delhi recorded no “good” air day, with 2016 faring no better and again recording zero “good” day. It was only in 2017 that Delhi recorded a “good” air day — on July 30 and 31, when AQI was 43 and 47, respectively. In 2018 again, not a single day made the cut, but 2019 saw a fruitful August, with an AQI of 49 recorded on August 18 and 19, respectively.
Long-term CPCB data shows Delhi’s air quality has been improving each year since 2016, with the average PM10 and PM2.5 levels recording a gradual-but-steady annual drop.
While “good” air days generally tend to come in patches, often occurring back to back, owing to a spell of heavy rain, the spread has been over several days this August. The first “good” air day was recorded on August 13, when AQI fell to 50 after strong showers hit the capital. A week later, the second such day was recorded on August 20, when AQI was again at 50. While these two spells were impacted by rain, the third “good” air day on August 24 saw AQI at 45 — the lowest so far this year — which was primarily due to good wind speed.
On Tuesday, Delhi’s AQI was recorded at 61, which was “satisfactory”. Agencies forecast a drop in the coming days, with a spell of moderate-to-heavy rain likely to occur from Wednesday onwards until Friday. In fact, Delhi may record even more good days before the month is over, forecasts show.
“Fairly widespread rain is forecast for Wednesday. AQI is forecast to stay in the “good” to “satisfactory” categories for August 26, while the “good” category is forecast for August 27 and 28,” said System of Air Quality and Weather Forecasting and Research on Tuesday.
Anumita Roy Chowdhury, executive director of research and advocacy at Centre for Science and Environment, said a good monsoon had helped, but the low readings could also be due to the lockdown.
“After the unlocking process began, the background emissions were on the rise again, but then the monsoon hit. While you generally do see low readings during the monsoon, the lockdown may have played a role this year. It will be crucial to see if readings in winter are reduced too,” said Chowdhury.

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