London is really not that polluted. It rains too much to be very polluted. AQI is currently 88 in the worst areas. In China many cities are often 150-200 range. India is off the charts, my friend who makes commercial air quality sensor arrays said most sensor tech maxes out way below ambient Indian levels and readings cannot therefore be trusted - nobody knows how bad it is.
That’s vastly insufficient as far as empirical evidence is concerned. There are many things that coincide with pollution, which is what the commenter is saying. You need to demonstrate how you picked out pollution from everything comingled with it. That’s what’s being asked about here.
EDIT: Disregard this stuffy reply, my humor detector was off.
The response was tongue-in-cheek: the commenter implied that the article was insufficient due to the journalist being less intelligent due to living in a polluted city.
http://aqicn.org/map/london/ http://aqicn.org/map/jiyuan http://aqicn.org/map/delhi