Delhi’s pollution crisis comes in 2 waves: Study

NEWDELHI: Delhi, considered among the most polluted cities in the world, sees two spikes in pollution during winter months, a new study has shown. In both spikes, lasting a week each, pollution levels shot up at least five times above the permissible limits, forcing authorities to implement emergency measures.

Researchers from Indian Institute of Technology (IIT)-Delhi, the University of California, University of Illinois, and other research organisations found that while the first peak hits the National Capital Region (NCR) sometime around late October and early November, the second one, comparatively milder, occurs around December-end and early January.

The researchers analysed 16 years of satellite data (from 2001 to 2016) to obtain weekly concentration of PM2.5 levels in Delhi-NCR between October and May of the following year. The research was published in Atmospheric Environment, a peer-reviewed scientific journal, in February 2019. PM 2.5 — particulate matter that are 2.5 microns or less in width — are pollutants that can penetrate deep inside the lungs. “The study indicates two peak pollution episodes in Delhi-NCR. The first peak occurs in the week of October 29-November 4. The second peak is slightly lower than the first peak and hits between December 30 and January 5,” said Sagnik Dey, associate professor at the Centre for Atmospheric Studies in IIT-Delhi. Pollution levels starts peaking from October 15- 21 and peak between October 29 and November 4. This peak continues till around November 11 after which pollution levels start declining. The concentration of PM 2.5 again starts building up from around December 17-23 and hits a peak around December 30-January 5.

In 2018, Delhi witnessed one peak on November 9, a day after Diwali, when pollution hit the emergency level. Another peak was witnessed between December 23 and 25. Pollution levels hit the emergency levels at least two times after that, largely because of unfavourable wind conditions. Delhi encountered its worst fog in 17 years in the last week of October. While east and north-east Delhi remain more polluted during the October-November episode, the pollution rises across the national capital, except South Delhi, during the DecemberJanuary episode. “Pollution levels in Delhi are governed primarily by two factors : meteorology and groundlevel activities...,” said D Saha, former head of the Central Pollution Control Board’s air quality laboratory.