In an affidavit filed in the Supreme Court, the Union ministry of environment, forest and climate change has said that stubble burning is not a major contributor to high levels of pollution in Delhi. “As per a scientific study carried out and to get indicative figures to show average sectoral contributions in PM 2.5 and PM 10 concentrations in Delhi” the respective contribution of agricultural burning to PM 2.5 and PM10 was just 4% and 7% each in winter and
So where did the government get its 4-7% figure from?
That is most likely an average number for the entire year. If the same logic were to be applied, pollution is not as big a problem in Delhi. The same affidavit shows that between 2016 and 2020, the number of “severe” AQI days in Delhi was never more than 25. Even if one were to add the number of “very poor” AQI days (readings between 301 and 400) to the number it comes between 64 (2020) and 126 (2016) during this period. Clearly, days with higher AQIs are a bigger problem than days when the AQI is not so bad. And, as has been shown above, contribution of farm fires is significant when AQI levels are higher.
Spike in farm fires coincides with rise in AQI levels
Unlike AQI and PM 2.5 numbers, data on the contribution of farm fires to PM 2.5 levels in Delhi is not available for the period before October 20. What we do have is daily data at a high resolution from 2012 onward on the number of fires seen in Punjab and Haryana from satellites. Reading this data with PM 2.5 levels in Delhi from 2018 onwards (air quality stations were much fewer before 2018) shows that there is a broad resonance in the period when farm fires and pollution levels peak in the city.
Low contribution of farm fires to pollution is an aberration, not the norm
To be sure, there does exist research to show that even on days when farm fires are rampant, their contribution to Delhi’s PM 2.5 levels can be low. However, this is more an aberration due to favourable climatic conditions than proof of farm fires being benign for Delhi’s pollution levels. A 2018 article, Objective evaluation of stubble emission of North India and quantifying its impact on air quality of Delhi, published in the international journal Science of the Total Environment gives a useful insight into this question. “Although the stubble burning was a regular process during the said period (October 10-December 10, 2018), with varied fire count, the impact of biomass burning on Delhi’s PM 2.5 is found to vary on day -to day basis with percentage contribution of stubble burning ranging from 1% to 58% as it is highly dependent on transportation pathway of air mass, controlled by source to target region meteorological parameters led by wind direction and wind speed,” the paper says.
“The impact of stubble burning on Delhi’s air quality depends not only on amount of biomass burned in Punjab and Haryana but a combined effect of high wind speed at intrusion height, wind direction and air residence time in the Delhi airshed,” the paper says.
Given the fact that no policy can control meteorological factors such as wind speed and direction, it makes eminent sense to make efforts to control farm fires rather than hoping for a divine intervention on the meteorological front. None of this, of course, is to say that other factors are not responsible for pollution in Delhi, or other steps need not be taken.
