Qu'il fait bon respirrer l'air faris de Delhi...

Why 2012 was a year of pollution extremes for Delhi


Three extreme polluting events made 2012 one of Delhi’s worst years, according to scientists with the System for Air Quality Forecasting and Research (SAFAR) project under the Ministry of Earth Sciences. SAFAR is India’s sole project for forecasting the quality of air. Launched by the ministry for the Commonwealth Games in 2010, it has been introduced in Pune too. 

Recording New Delhi’s history of air pollution, scientists say they were able to predict the three events three days in advance — a dust storm in March, a “poisoning event” in October-November that saw an outbreak of respiratory ailments, and Diwali with its fireworks, which doubled the pollution level.
“It is for the first time in the known history of National Capital Region, Delhi, that it experienced three extreme pollution events in 2012. Although the background seasonal pollution was no different than that of the previous two years, in terms of extreme events it was one of the worse years in environmental air pollution,” Dr Gufran Beig, project director of SAFAR, told The Indian Express.

The dust storm started on March 19 and peaked on March 20. It was triggered by a heavy dust storm that originated outside the continent and travelled all the way. On March 20, the day’s average level of coarser particles (size 10 microns or less) suddenly increased by more than 300 per cent, from 200 micrograms per cubic metre to 830 — the permissible limit is 100 micrograms per cubic metre. Until March 22, the air remained in the “very unhealthy “ or “critical” category.

The fortnight between October 27 and November 8 brought what SAFAR scientists have called the the Delhi polluting event. The air quality crossed dangerously high emergency levels assigned for human health by WHO without any additional local emission source. It triggered thousands of hospital admissions with respiratory ailments as levels of two categories of particulate matter, PM10 and PM2.5, touched 800 and 500 micrograms per cubic metre respectively, more than double the level assigned for the emergency or critical category and unexpected under normal conditions. 
Scientists explained the circumstances leading to the event. A western disturbance had introduced lot of moisture to Delhi. A sudden change in the wind direction pumped in a huge amount of fire smoke, emerging from the crop residue burning in crop-rich Punjab and Haryana. This increased organic carbon significantly, which led to solar dimming and brought a sudden fall in temperature by 4-5 degrees Celsius overnight, along with dense fog.

Diwali’s pyrotechnic display, from November 12 to 15, elevated the pollution level again by more than 100 per cent, with a significant contribution of black carbon. Pollution peaks varied highly from location to location, indicating a local source. The elevated levels did not linger, and the pollutants got dispersed within three days and came down to pre-Diwali levels on November 16.

Beig said the last year has provided enough ground to believe that extreme air pollution may be an indicator of climate change. It is an example of how nature can play havoc in no time and sometime surpass all mitigation efforts, Beig said.