Number Theory: Thank the weather for post-Diwali clean air

Delhi woke up to relatively cleaner air and clearer skies after Diwali this year as compared to previous years. But it was neither citizens observing the official ban on firecrackers, nor these firecrackers somehow not leading to massive spikes in pollution that led to this. In fact, it was a stroke of pure weather-induced luck. Here are four data points that explain this in detail.