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Wednesday, Dec 11, 2019

Delhi’s air bad, farm fires make it worse

Delhi’s air quality in this period was bad even without the effect of stubble-burning, which only made it worse.

delhi Updated: Nov 20, 2019 10:49 IST
Abhishek Jha
Abhishek Jha
Hindustan Times, New Delhi
Vehicles ply amid a dense layer of smog at Rajpath, in New Delhi.
Vehicles ply amid a dense layer of smog at Rajpath, in New Delhi.(PTI Photo)
         

Between October 23 and November 18, discounting the effect of stubble-burning on Delhi’s air reduced the number of days with “severe” air quality (PM2.5 concentration exceeding 250 micrograms per cubic metre) from 13 to seven, but the city’s air quality still remained in the “poor” and “very poor” levels, according to a Hindustan Times analysis of recently improvised System of Air Quality and Weather Forecasting and Research (SAFAR) data.

Put simply, Delhi’s air quality in this period was bad even without the effect of stubble-burning, which only made it worse.

The analysis was made possible by SAFAR’s release of data on absolute contribution of stubble fires to PM2.5 concentration in Delhi since October 23. PM2.5 refers to particulate matter with a diameter of 2.5 microns. Prolonged exposure to high levels of PM2.5 could cause severe bronchitis, and perhaps even lung cancer. Shorter exposures are also harmful, especially to young children and the elderly.

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An analysis of 27 days (October 23-November 18) shows that excluding PM2.5 emissions from stubble fires reduces the number of severe pollution days but still did not do anything to increase the number of days with “good”, “satisfactory” or “moderate” air quality in Delhi. (Chart 1)

 

These numbers show that while preventing stubble fires can prevent Delhi’s air pollution levels from being severe, this is not enough to bring it to desirable levels.

This means that policy interventions designed to control stubble burning are necessary but not sufficient to control air pollution in Delhi.

To be sure, there are other factors at play as well. For instance, the data shows that similar number of stubble fires can have very different impacts on Delhi’s pollution levels, depending on wind speed and direction. A comparison of October 24 and 25 shows this.

An increase in wind speed, eastwards on both days, was accompanied by a decline in pollution levels even though the number of stubble fires increased. (Chart 2)

 

 

This means that even without any change in stubble fires, Delhi’s air pollution levels can change drastically depending on meteorological conditions. That isn’t to excuse Punjab’s tardiness in clamping down on stubble fires — they have to stop — but only underlines the importance of coming up with a better response system . An either-or approach will not work