If they aren't in poverty you have more options for reducing pollution.

When someone is so poor that they can just barely feed themselves and their family, you can't realistically expect them to do much to reduce pollution. You can't really enforce pollution regulation because they can't pay fines and tossing them in prison only makes things worse.

When they're able to afford some luxuries they're capable of devoting more thought towards their environment and can afford to spend more for more environmentally friendly living.

That article was specifically about India’s capital. It’s also possible that problem can be fixed in the future, so people are lifted into a clean urban environment.

Also, last I recalled, London faced similar issues before and is in a much healthier state nowadays.

It's also more about geography. Had there been no Himalayas, the problem would be much less acute

This line of reasoning needs to be stopped. If you haven't lived or grown up through India's pre-capitalist era you have no idea what you're talking about. Ask any Indian about it and I think they'll tell you that urban pollution is a small price to pay for the distance they've come in terms of overall quality of life and wealth.

A major source of pollution is stubble burning, which is of rural origin.