Winter was more polluted this year, but saw fewer smog days: CSE analysis
The seasonal average pollution levels in Delhi this winter was higher than previous years, but the severity and smog episodes this year was lower, an analysis by the Centre for Science and Environment (CSE) has shown.
The analysis also shows that north Delhi recorded the worst pollution levels in the city this winter, with Jahagirpuri emerging as the hot spot with the worst air.
There were two continuous smog episodes during this year’s winter. The first episode was of longer duration as it started on November 3 and lasted seven days. The second started on December 22 and lasted three days. Thus, the continuous smog episodes were fewer and shorter compared to previous winters. The 2019-20 winter had three smog episodes of eight, six and five-days durations respectively; the 2018-19 winter had four smog episodes of 10 days, two episodes of six days, and one of three-days duration.
Among the four neighbouring satellite towns of Delhi, Ghaziabad was the most polluted, the CSE’s winter air quality analysis — which was made based on the air quality recordings of the Central Pollution Control Board’s (CPCB) official online portal Central Control Room for Air Quality Management (CAQM) between October 15 and February 1— further read.
“There is always a special interest in understanding winter pollution trends, given the extraordinary situation we faced due to the pandemic this year, as well as the fact that winter remains the most difficult season in this region due to atmospheric conditions of inversion, calm wind, and cold weather,” said Anumita Roychowdhury, executive director (research and advocacy), CSE.
She added, “The winter air traps local and regional pollutants and gives rise to the deadly winter smog that we, the residents of Delhi-NCR, are so familiar with.”
The trends show that the number of days with ”severe” and “very poor” levels of PM 2.5 (particulate matter with diameter less than 2.5 micrometres) concentration was comparatively lower this winter. According to the Graded Response Action Plan (Grap), which is a set of emergency measures that kick in as the PM levels reach a certain mark, air quality is considered to be in the ‘severe’ zone when the PM 2.5 levels are above 250ug/m3 or the PM 10 levels (particulate matter with diameter less than 10 micrometres) are above 430ug/m3. It is categorised as ‘poor’ when the PM 2.5 levels are between 91ug/m3 and 120ug/m3 or the PM 10 levels are between 251ug/m3 and 350ug/m3.
However, the number of days in the “poor” pollution category has increased. At the same time, the overall city-wide average for the season was comparatively higher this year, the analysis found.
For Delhi, this average stood at 186μg/m3, which is 7% higher than the seasonal average of 2019-20 winters.
Avikal Somvanshi, programme manager in CSE’s urban lab team of the sustainable cities programme, said, “On a year-on-year basis, the annual average PM2.5 levels are declining in Delhi. Is this also moderating the impact on the pollution build-up and severe peaks during winter? This analysis of winter pollution trends since 2018 helps understand the patterns of change.”
He said,“Overall, higher seasonal average but lower peak can be attributed to meteorology and changes in farm stubble burning patterns. But considerable variation has been noted among individual stations in the city. This also indicates the dominance of local pollution sources.”
At a more hyper-local level, except at Wazirpur and Sahibabad, all the locations in the Delhi-NCR pollution hot spots list saw a spike in the seasonal PM2.5 levels, compared to last winter.
Jahangirpuri, with a seasonal average of 256μg/m3, was the dirtiest among the hot spots. Bahadurgarh — that recorded an almost 50% spike in its PM2.5 level — was the cleanest.
The findings also showed that steep deterioration was noted in many locations in the Capital that are not yet designated as ‘hot spots’ by the pollution monitoring agencies.
The Delhi Pollution Control Committee (DPC) defines hot spots as those areas where the annual average pollution levels are higher than the mean value of the city.
During the winter months, at least 14 more locations registered higher seasonal averages than the mean of recognised hot spots (197μg/m3).
These were Alipur, Delhi Technological University (DTU), ITO, Nehru Nagar, Patparganj, Sonia Vihar and Vivek Vihar in Delhi, sectors-1 and 116 in Noida, Loni, Sanjay Vihar and Indirapuram in Ghaziabad, Knowledge Park in Greater Noida, and Bulandshahr.
“These trends show that urgent next steps are needed for scale and speed of action across all sectors and across NCR. The region needs massive clean fuel and technology transition in industries, time-bound implementation of power plant standards, massive transportation and mobility transition across Delhi and NCR, and a paradigm shift in waste management with strong compliance and accountability,” Roychowdhury said.