Why it is in news?

• Pollution levels recorded in the National Capital Region on Deepavali and the two following days were in close agreement with forecasts that assumed that the entire stock of unsold firecrackers in the city was used.
• This data indicates that a October 9 Supreme Court ban on the sale of firecrackers in the city had no effect, and partly explains why air pollution remained severe despite it.
• The idea behind the Supreme Court judgment was to test whether reduced firecracker use could alleviate the noxious pollution in Delhi during winter. 

Three scenarios

• To forecast pollution levels on October 19, 20 and 21 as a result of this ban, a research group, Urban Emissions, simulated three scenarios using weather and emissions data.
• In the first, the ban led to no reduction in firecracker use; in the second, there was a 25% reduction while in the third, the drop was 50%.
• The pollution peaks only matched at 0%. This means that there was no effect of the ban on what people managed to burst  

Pollution last year

• In 2016, Deepavali fell on October 30, by when crop-burning (which typically occurs in the last two weeks of October) had already peaked in Punjab and Haryana.
• Further, slow westerly winds carried this pollution towards Delhi. Within Delhi itself, wind speeds were low, affecting dispersion. In contrast, Deepavali in 2017 fell on October 19, when crop burning had just begun. Helping Delhi further, strong winds within the Delhi region dispersed the pollution faster.
• Meanwhile, another forecasting model, the System of Air Quality and Weather Forecasting and Research (SAFAR), also ran three simulations for pollution levels on six days around Deepavali, assuming that the stock of firecrackers burnt was 25%, 50% and 100%, respectively, of 2016 stock.
• According to  SAFAR, actual pollution levels seen during these days matched the 100% scenario. Rather than use actual stock numbers as Urban Emissions did, SAFAR attributed a portion of the emissions last Deepavali to firecrackers, and used this to develop this year’s forecasts.