India, Oct. 25 -- If the months of the year were days of the week, October would be Friday - slightly relaxed, a little indulgent,and smelling of holidays in the vicinity. In North India, its evenings are usually punctuated by a nip in the air, the sun spilling colour over the horizon before being lost to haze, and the occasional sound of a Diwali bomb going off somewhere in the distance.

It was always like this - until the air quality index (AQI) was adopted. Now, the SI unit to measure October is AQI.

There was a time when October wasn't a public health emergency. It was a mood - the only month in this tropical country you could truly appreciate. India is unique that way, a lot of anti-incumbency builds-up over monsoons due to crumbli...