From cleanest to worst, study shows how pollution in Delhi rose in a few months
The PM 2.5 levels this winter spiked by about 8-11 times from August (the cleanest month on record) to November across Delhi and its neighbouring towns, as per a fresh analysis of winter pollution levels by the Centre for Science and Environment (CSE) released on Thursday.
According to the analysis, the relatively clean air gains made during the Covid-19 induced lockdown and a good monsoon were lost to opening up of the economy coinciding with poor weather, contributing to high winter pollution levels this year.
Even though the overall average levels of PM 2.5 (the most harmful aerosols in Delhi’s air) for 11 months this year was considerably lower than the previous year, it went up to make the air from very poor to severe during October-November, it said.
The analysis shows that from the cleanest August (the cleanest month since air quality records started to be maintained in May 2015), the PM2.5 levels rose dramatically to one of the dirtiest Novembers in recent years. “The rise varied from 9.5 times in Delhi to 11 times in Ghaziabad; followed by Noida (9.2 times), Gurugram (6.4 times) and Faridabad (6.2 times). This shows that the transient change of the lockdown phases could not be sustained without the systemic changes needed to control pollution from vehicles, industry, power plants, and waste,” the analysis read.
This August recorded four good air days and the lowest AQI (41) since 2015, owing to widespread rainfall and good wind speed in Delhi.
Another finding of the analysis shows a higher share of PM 2.5 (tinier, ultrafine particles that can penetrate deep into the lungs) in the overall PM 10 (coarser dust particles) concentrations this year.
“The share of the ultrafine particles in PM 10 levels determines the toxicity of the air. With the onset of winter, the percentage share of PM2.5 in the overall PM10 rose to over 70% during the smog episodes in early November, and remained high at 50-60% most of November. Its share was highest on Diwali, reaching over 80% at many locations,” it said.
The CSE analysis also showed that the pollution levels were more fluid this year compared to the trends in previous years. This year, local pollution across the monitoring centres in Delhi shows wider variations. This is in contrast to the range noted last year, CSE said.
For instance, even on the peak smog day in November this year, the PM2.5 levels in several stations varied from a lower bound 108 μg/m3 at NSIT, to 699μg/m3 at Mundka.
But last year the variation was noted at a higher range —between 351μg/m3 at Shadipur to 725μg/m3 at Alipur— while the overall level stayed above 374μg/m3. “In fact, the standard deviation among the 36 stations of Delhi this November on an average is 60% higher compared to last year,” it said.
Anumita Roychowdhury, executive director (research and advocacy), CSE said that this winter, there is a change in the pollution pattern that shows in lesser number of smog episodes compared to last year, wider variation in location-wise concentration compared to last year with higher contribution from stubble burning, among other factors. There are also days when pollution levels dropped to moderate levels even without rains but better wind conditions.
“This pattern points to the fact that the reforms and action in key sectors of pollution will have to be scaled up across the region to further bend the annual air pollution curve,” she said.
The analysis shows that the share of stubble fires from the neighbouring states of Punjab and Haryana in Delhi’s PM 2.5 levels were higher compared to the previous years. It shows that the smoke from crop stubble fires started impacting Delhi more discerningly from October 10 onwards this year, which was a week earlier than last year when it started on October 16.
“There were seven days this year when the contribution of smoke in Delhi’s PM2.5 concentration exceeded 30% in contrast to three days in 2019 and 2018. There were six days when the contribution was between 20-30%, up from four days in 2019, and 16 days of 10-20% contribution, which was also an increase from 15 days in 2019. There were 23 days with less than 10% contribution, down from 30 days in 2019,” the analysis read.
It added, “This year Diwali pollution was also compounded by the heightened contribution (32%) of smoke from crop stubble fire.”
Roychowdhury further said that while it needs to be seen how the pollution levels will play out during the rest of the winter, it is clear that the region cannot afford to lose gains it has made so far. “At the same time, we also need to raise the level of ambition to drive action across all key sectors. Enforce power plant standards, eliminate coal from the industry, scale up public transport and vehicle restraint measures and manage waste to have a zero waste and zero landfill strategy,” she added.