In this first published study of exposure to outdoor tobacco smoke, investigators measured air pollution levels during visits to outdoor pubs, cafes, and sidewalks where smokers were present. They also performed controlled experiments of air pollution as a function of distance. The main conclusions from the study are that a person can be exposed to concentrated streams of tobacco smoke particles that are many times more polluted than normal background pollution levels. Being exposed outdoors for an hour to several cigarettes at close range could result in an exposure comparable to being present in a smoky tavern for an hour. It would be possible to exceed the current EPA standard for daily exposure to particles if one were exposed within a few feet of multiple smokers during the day.