I was just reading about pollution sources, and you’re right that 75% comes into London from outside, compared to only 20% of NOx. Although levels of PM are dou

I was just reading about pollution sources, and you’re right that 75% comes into London from outside, compared to only 20% of NOx. Although levels of PM are double the concentration along roads compared to the background, so there is a local as well as a regional effect.