Air

Even the wind cannot help Delhi’s air

Despite higher wind speeds, pollutants from Diwali celebrations lingered in the atmosphere and rendered it toxic

 
By Shambhavi Shukla
Last Updated: Wednesday 02 November 2016
Photo credit: Jean-Etienne Minh-Duy Poirrier/Flickr (Creative Commons)
Photo credit: Jean-Etienne Minh-Duy Poirrier/Flickr (Creative Commons) Photo credit: Jean-Etienne Minh-Duy Poirrier/Flickr (Creative Commons)

rIn an already polluted Delhi, firecrackers exert additional stress on the city’s air quality. Though the concentration of pollutants increases during Diwali, the accumulation of pollutants close to the surface also depends on meteorological parameters such as wind speed, temperature and mixing height. Mixing height signifies the height above the surface to which pollutants vertically disperse.

Delhi-based non-profit Centre for Science and Environment (CSE) analysed air quality data with mixing height on Diwali day over the past seven years. Low mixing height leads to an enhancement of the concentration of pollutants in the atmosphere whereas high mixing height gives more space for pollutants to disperse, leading to low concentration of pollutants near the surface.

Source: Central Pollution Control Board

In 2010, the concentration of Respirable Suspended Particulate Matter (RSPM) was found to be quite high as the mixing height was low and pollutants did not have enough space to disperse in the atmosphere. The mixing height in 2014 was 490 metres and the RSPM concentration was 481 microgramme per cubic metre which was 4.8 times the standard. But with similar mixing height in 2016, the concentration of RSPM was found to be 10.6 times the standard. According to the Central Pollution Control Board, the wind speed in 2014 varied from 0.2 to 0.6 m/s whereas in 2016, wind speed was comparatively higher at 1.3 m/s. The mass concentration in Delhi is so high that the natural effect of mixing height, influenced by the wind speed, has not been able to help Delhi. 

Air pollution levels have already entered the severe category this winter. The levels during winter are higher than those during the rest of the year due to meteorological reasons, and are augmented by emissions from trucks passing through Delhi, power plants, biomass burning and construction activity. While weather conditions are beyond human control, action to prevent pollution from anthropogenic sources should be priority. Delhi must pursue a stricter course of action to prevent these emissions.

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