https://www.telegraph.co.uk/news/health/news/10817787/How-ch...

Generations of men have been taught that when walking with a woman on a pavement, they should always take the side closer to the road allowing her to keep further away from the traffic.

But Dr Iarla Kilbane-Dawe claimed that Londoners should avoid walking too near the kerb because on busy streets, air pollution can be up to a third higher than on the inside of the pavement.

Shame you cant remember the source. Ive long since wondered if its actually more deleterious for my health to cycle to work in London due to air quality. I came to the conclusion that youre damned if you do and damned if you dont in the end, as in London at least, many of the tube lines have particulates higher than is considered safe