Patterns in Delhi’s air quality

Air quality varies significantly with the time of the day, the month of the year and the region within the city, finds new research based on Delhi’s air quality data from January 2013 to September 2016.

The effect of air quality on public health is usually measured by looking at the average concentration of pollutants and comparing it to the specified permissible limits.

For instance, Delhi’s annual average PM 2.5 concentration was 153 ug/m3 in 2015 according to the WHO, whereas 60 ug/m3 is the permissible limit, signifying the poor quality of air that Delhiites breathe.

How does it affect us?

While the macro numbers bring to light the severity of the problem, they say little about the exposure of the public to these pollutants, which the research aimed to ascertain.

Conducted by Dhananjay Ghei and Arjun Gupta, researchers at the National Institute of Public Finance and Policy (NIPFP), and Renuka Sane, academic at the Indian Statistical Institute, Delhi Centre, and followed by a peer review, the findings were published on the blog of Ajay Shah, economist and senior fellow at NIPFP.

Hourly PM 2.5 (considered the most harmful pollutant) data was sourced for five locations across Delhi from January 2013 to September 2016, which included Chanakyapuri (situated at the US Embassy) and the four monitoring stations of the Central Pollution Control Board (CPCB) — RK Puram, Anand Vihar, Punjabi Bagh and Mandir Marg.

Three types of variations were observed.

Variation by the time of day

If you want to go out for a jog, early evening is your best bet, given that pollution levels are low during the day and begin to increase after 6 p.m.

The pollution level continues to rise till 9 a.m. the next day, after which the air quality starts improving a bit.

Data over the last three and half years shows that the average PM 2.5 concentration from 6 p.m. to 9 a.m. is 140 ug/m3. From 9 a.m. to 6 p.m., the figure stands at 108 ug/m3.

“This suggests that a measure that restricts traffic during the day, such as the odd-even policy, is unlikely to be as effective as a measure that restricts emissions at night,” the study says.

Variation by month

The monsoon months have the lowest levels of PM 2.5 particulate matter, the study found.

This is because smaller particles like PM 2.5 are removed by precipitation.

Winter is worse. Due to low wind speed and relatively high humidity, winter has the highest levels of PM 2.5 matter in the air, and crosses 200 ug/m3.

Variation by location

While the broader discourse remains centred around the daily average, there is marked variation in air quality by region. Of the five locations for which data was analysed, Chanakyapuri was found to have the lowest PM 2.5 concentration compared with the others. Anand Vihar in east Delhi fared worst, with severe levels of air pollution in the night.

The study notes that the location effect can occur “due to the varying population densities at these locations as well as the proximity to industries, etc.”, while adding, “This could lead to location-specific policy initiatives such as the closing down of factories or the modification of vehicular traffic.”

This research brings in evidence and takes us a step forward in our understanding of the extent and nature of the air quality problem in Delhi, which can help design effective public policy and deliver on it.

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Printable version | Apr 14, 2021 1:56:12 AM |

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