On my daily commute to work every morning, I use the road around Namsan Mountain, the famous mountain in the middle of Seoul. One thing I always find uncomfortable is watching some foreigners jogging in the same place when the air pollution is at a serious level.
I check the air pollution level almost daily using Korean websites since the air quality of the whole Korea got worse because of the smog from China. I guess the joggers I saw would have skipped running if only they had had an access to English website offering the information.
Today, I found this English website that shows air quality of major cities in Korea. It will be useful for foreigners worried about air quality of Seoul. Check it out.