Delhi Pollution: Are we drawing the correct conclusions?

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Delhi Pollution: Are we drawing the correct conclusions?

The supreme court, on Friday, imposed a blanket ban on the sale and stocking of all firecrackers in the Delhi-NCR region, and suspended all licenses to do the same. This is quite a laudable, and a side note, courageous move, seeing the religious connection people have made with firecrackers.

On a superficial level, this might be the solution to at least bring the pollution down to a bearable level in the NCR region, but when looked at from an analytic lens, this ban might not quite be as effective as it might appear.

We performed a series of analyses, and came to some rather interesting conclusions. Our methodology included collecting the Air Quality Index (AQI) data in four areas in Delhi in 2016 as well as 2015 and drawing spatial as well as temporal comparisons to give a clear picture of what was happening. We also collected data from 2014 but it was sparse, and yet it supported our findings definitively, if not conclusively. One of the most relevant is the fact that this year was truly anomalous, if only firecrackers are considered major pollutants during and after 30th October. Comparing the AQI this year to that observed in 2015, it was obvious that firecrackers could not have caused the shocking level of pollution seen this year. The findings, in a form of a line chart, have been presented below:


Illustration 1: AQI levels in 2015


Illustration 2: AQI levels in 2016


As it is obvious from the graphs, the most prominent spike in 2016 begun, not during and immediately after Diwali but, five days after Diwali, at which point in 2015, the AQI was beginning to stabilize. While there was a spike on the 17th (six days after Diwali 2015)which stayed till the 21st, it was easily attributable to the sudden 2° C temperature drop from the 22° C on the 16th to 20° C on the 17th and beyond.

However, what was observed in 2016 was way beyond anything that a temperature drop could reasonably explain. Thus began, late on 4th November, and continuing well into the late hours of 6thNovember, a time period when AQI of 500 was constantly recorded. As an aside, 500 is the maximum value for the AQI. Even if the concentration of individual pollutants exceed the values required to record this value, the value of AQI will remain constant at 500. Another interesting observation that is seen is that the AQI values in 2015 were not close to 500 at any point in time after Diwali.

However, what was more disconcerting were the levels of PM 2.5(a major pollutant whose concentration in PPM tracks the AQI) in 2016. They were following a trend close to that of 2015, until late on the 4th November. At that point they steadily shot up to, and maintained a level higher than those observed during Diwali. This started, according to the devices installed by the CPCB, in places in Haryana near the NCR region, and steadily progressed towards the NCR region. An anomalous rise in the levels of PM2.5 was observed late on 4th November, and it proceeded towards Delhi, and during the early hours of 5th November, the PM2.5 levels in most places in Delhi had begun to reflect this spike. This gradually built up, until the evening of 6th November. This is in stark contrast to the PM2.5 levels in the previous year a week after Diwali. All of this suggests very strongly that the Diwali celebrations might not have been the major contributor to the current menace in Delhi.

So now rises the logical question, what could have possibly been the major source of the pollution level? A hypothesis presented by the data, and supported by a study done by IIT Kanpur strongly suggests that the practice of paddy stubble burning in Punjab and Haryana, possibly combined with the lowering temperatures and the firecracker residue might be to blame for this menace. And while it can be argued that stubble burning happens every year, it would seem that the proximity it had with Diwali, along with the weather conditions, is the anomalous entity that caused this severe buildup of smog.

And this is why, despite the laudable measures taken by the government to ban firecrackers, it is possible that there might not be a major change in the amount of pollution Delhi is facing, for the simple reason that it is not the major contributor to the pollution levels seen this year.