It’s too early to celebrate Delhi’s month of clean air

livemint.com:

climate change, Delhi has at last had clean air for an entire month. All days in July had “good to moderate" air quality – unheard of for the capital’s 32 million breathless people. "The number of ‘good to moderate’ air quality days for [July] was 26 in 2019; around 31 in 2020; 29 in 2021; 31 in 2022; and 31 in 2023.

The monthly average AQI for Delhi during this period also remained ‘satisfactory’ at 83.71. Delhi has recorded its lowest monthly average AQI during July of the current year compared to the corresponding period for the last four years from 2019 and the monthly average AQI of July 2023 is comparable with the monthly average AQI of July 2020," the ministry added. Should we be rushing to pop the champagne bottle? Perhaps not yet.

One swallow does not a summer make, and July isn’t the whole year. There are reasons to take a more measured view. For one, the AQI of a city is only the average of the readings at all its AQI measuring stations.

And Delhi remains a sprawling city with uneven development. So, for instance, randomly accessed data on Sameer on 4 August showed the city’s AQI was “moderate" at 85, but the PM2.5 level, at 27, was 1.8 times the World Health Organization’s recommended limit. To be sure, WHO’s recommended limits, revised recently, are stringent and rightly so.

But it does mean, according to the agency itself, that 99% of the world population lives with dangerous levels of ambient air pollution. On 4 August, the measuring station at Anand Vihar showed an AQI level of 248 with an average PM2.5 level of 83 and a PM10 level of 248. Eight other stations showed levels of over 100.

An average is not an accurate measure. Also, accuracy is crucial when it comes to matters of health. How significant? An