I used to regularly run home through central London. Never noticed the pollution. My OH did one run with me and says he couldn't breath because of the traffic fumes. I thought it was psychosomatic but it could be some people are more sensitive to it.
Only time I really noticed pollution was a 20 miles with a large chunk next to a bust A road (70 mph traffic). Found my chest felt tight at the end. Didn't repeat that route!
Slowly clawing it back, after a poor Feb mileag. March so far has been 80 miles, and I'm on 218 for the year so far.
Need to stick to 20 miles per week and I'll make my 1000! Feeling jealous of all of you who made better starts and have some leeway!