Only two ‘good’ air days since May 2015 in Delhi

A foggy morning on the Yamuna as temperature dipped in the capital. Winter is usually accompanied by a deterioration in air quality. Praveen Khanna

Between May 2015 and October 2017, Delhi saw only two days of 'good' air quality, reveals Central Pollution Control Board (CPCB) data. Both the good air quality days were seen in July this year.

Data shows that there has been a marginal improvement in air quality when it comes to the number of days that saw severely polluted and very poor air quality days. Between May 2015 and April 2016, the number of very poor air quality days was 116, and 15 of these were in the severe category. Between May 2016 and May 2017, this number went down to 100. Of these, 21 days were in the severe category - primarily because of the unusually high post-Diwali pollution, which was partly because of adverse meteorological conditions.

The biggest change, however, can be seen in the number of days that have seen satisfactory air quality. Between May 2015 and April 2016, there were neither any good nor any satisfactory air quality days. The duration between May 2016 and April 2017 saw 24 satisfactory air quality days.

Since May 2017, the city has already seen 45 satisfactory air quality days. According to scientists and air pollution experts, air quality depends on a number of factors and even a small change in these factors can mean a considerable difference in air quality. "Within meteorology, there are factors such as wind speed, wind direction, temperature and moisture that can bring variations within air quality parameters. Then there is, of course, the amount of emissions that will ascertain air quality. While the data looks encouraging, we need a deeper study on the trends," said a Delhi Pollution Control Committee (DPCC) scientist.

While the data starting May 2017 shows improvement over the past two years, the most polluted months of winter are yet to come. According to scientists at CPCB, while there has been significant improvement in air quality since 2014, managing pollution in winter season is a very big challenge.
"We are mostly thinking in terms of technological intervention, so far. The focus now needs to be on ecological sustainability. We need to look at population and vehicular density in NCR. Increasing green cover not just in Delhi but also in NCR to control dust pollution. The involvement of people is key now," said CPCB air quality laboratory head, Dipankar Saha.