Thursday 12 November 2015
An analysis of air quality data on the night of Diwali on Wednesday has shown a dramatic build-up of pollution following the bursting of crackers, hitting dangerous levels of exposure. The analysis was conducted by Delhi-based non-profit Centre for Science and Environment (CSE) which took into account official ambient monitoring data and conducted its own exposure monitoring of PM2.5.
The ambient pollution level on Diwali may have, however, seen a slight improvement over the previous year due to comparatively less crackers and mild wind in some parts. The recorded wind speed on Diwali this year was 1.19 metres per second as against 0.62 m/s in 2014. But from the public health perspective, direct exposure to toxic emissions matters most. "Delhiites will have to do a lot more to control crackers to reduce such dangerous levels of exposure and protect public health," said Anumita Roy Chowdhury, executive director, CSE.
CSE exposure monitoring
CSE carried out exposure monitoring of PM2.5—the level of pollution within our breathing zone at the time crackers were burst—and found alarming levels of exposure. The CSE team moved with monitoring devices in different parts of the city—covering diverse residential neighbourhoods such as Pahar Ganj, Rajendra Nagar and Karol Bagh in the West, Lajpat Nagar in South, Mayur Vihar, Patparganj and Laxmi Nagar in the East and around Dhaula Kuan in West Delhi, Sita Ram Bazar in Old Delhi. CSE used TSI hand-held pollution exposure-measuring devices which can measure both the mass and size fraction of particulate matter (PM).
Key highlight of CSE’s exposure monitoring:
- People breathed several times higher pollution than the ambient level monitored by DPCC: Overall, people breathed an hourly average that is at least three to four times higher than the ambient monitoring recorded at the Delhi Pollution Control Committee (DPCC) stations.
- Exposure peaks in different locations were frightening—more than 2,500 microgramme per cubic metre (cum): After 3 pm, Mayur Vihar Phase I recorded one hourly average level as high as 1,763 microgramme per cum. In Patparganj, it peaked at 2114 microgramme/cum. At Laxmi Nagar, the exposure peaks were about 2,640 between 10.15 pm and 11.15 pm, and in Old Delhi 2,654 microgramme per cum after 11.30 pm.
Official real-time monitoring also indicates high peak build-up during Diwali evening. CSE tracked the changes in real-time data during Diwali evening and found rapid build-up as the evening progressed. The official release on Diwali pollution does not capture these changes in the evening when the crackers were burst.
- Ambient levels increased rapidly in the evening: Official monitoring shows rapid build-up of pollution peaks at 8 pm. Real-time data for the evening of Diwali showed a spike in PM2.5 in the range of 399 to 608 microgramme per cum between 8 pm and midnight.
- Stunning build up of SO2: During pre-Diwali days on November 6 and 7, the SO2 level was as low as 23 but on Diwali, the higher range in 24 hours reached 64 microgramme per cum—an increase of 2.6 times. SO2 in combination with PM is a dangerous combination. In some locations like that of R K Puram, the build-up of SO2 in the evening was dramatic. The short duration peaks hit more than 250 microgramme per cum.
Official ambient monitoring shows comparatively lower range for most pollutants compared with last year
DPCC has released results of the ambient monitoring on Diwali day and compared them with last year. The plausible reasons are comparatively less cracker burning and also mild and improved wind compared to last year. The key highlights are as follows:
PM2.5: The 24-hour average ranged from 184µg/m3 to 369 µg/m3. The minimum was observed at Civil Lines and maximum at R K Puram. On Diwali day in 2014, the average concentration (for 24 hours) for PM2.5 ranged from 145 µg/m3 to 500 µg/m3
PM10: The 24-hour average ranged from 296µg/m3 to 778µg/m3. The minimum was observed at the airport and maximum at Anand Vihar. On Diwali day in 2014, the average concentration (for 24 hours) for PM10 ranged from 421 µg/m3 to 790 µg/m3.
Sulphur Dioxide (SO2): The 24-hour average varied from 26µg/m3 to 64µg/m3. The minimum was observed at IGI airport and maximum at Anand Vihar. On Diwali in 2014, the average concentration of SO2 (for 24 hours) varied from 8 µg/m3 to 87 µg/m3.
Oxides of Nitrogen (NO2): The 24-hour average varied from 37.0µg/m3 to 79.0µg/m3. The minimum was observed at Mandir Marg and maximum at R K Puram. On Diwali in 2014, the average concentration of NO2 (for 24 hours) varied from 39 µg/m3 to 194 µg/m3.
Carbon Monoxide (CO): The 24-hour average ranged from 1.1 mg/m3 to 4.0 mg/m3. The minimum was observed at Mandir Marg and maximum at Civil Lines. On Diwali in 2014, the average concentration (for 24 hours) for CO ranged from 0.9 mg/m3 to 3.0 mg/m3.
CSE had issued a warning a day before Diwali about the deadly impact of pollution caused by crackers at the onset of winter when the air is already saturated. The levels of tiny particles had already increased seven times since October 1 this year. This left no room for additional pollution in the city, especially from crackers that not only push up the pollution spike but also lace it with deadly cancer-causing substances.
"It is not enough to quibble over marginal changes in Diwali peak pollution from year to year. This requires strong community sensitisation as well as judicious mix of regulatory controls to protect public health," said Roy Chowdhury.