Number Theory: Should Delhi’s pollution spike surprise us?

Delhi’s pollution levels, as measured by the average Air Quality Index (AQI) hit the “severe” threshold on November 3. According to the data at 4pm on November 3, this number was 468, which is pretty close to its maximum limit of 500. While pollution reaching very high levels around this part of the year is not surprising, one bit which is slightly counter-intuitive this year is the fact that satellite data seems to show fewer farm fires. What exactly has led to the spike in Delhi’s pollution levels? Here are four charts which try to answer this question.