The air quality index in Delhi reached a high of 450 on November 3, and has been topping the 300 mark almost consistently between October 27 and November 8. On Wednesday, for the first time in 15 days, the air quality index was below 300, at 260. Credit: IndiaSpend While Delhi’s air quality, on which mainstream media focuses, improved slightly, smaller towns –Ambala, Khanna, Kurukshetra and Ludhiana – had severely polluted air (over 400) on November 9, according to the air quality index bulletin published by the Central Pollution Control Board. But what does having an air quality index over…