While we found that exposure can occur in most outdoor venues with smoking, as part of the study we also performed careful experiments of pollution level as a function of distance, so that the results of our study could be used to quantify exposures that would likely occur when nonsmokers are positioned at a variety of distances from the smoker(s).
As agrees with common sense, we measured the highest exposures within a few feet of a burning cigarette, corresponding to situations when a nonsmoker could be sitting within about 4 feet from the actual smoker, that is, the distance of about 2 typical arm lengths away from the smoker's body. The breathing zone of a nonsmoker at the same table, or perhaps an adjacent table, could come within 1.5 or 2 feet of the burning cigarette when the smoker puts the cigarette on the table or holds it in an outstretched hand. Toxic particle pollution at these close distances was surprisingly high with average levels during smoking sometimes exceeding 200 to 500 micrograms per meter cubed when we were downwind from the active cigarette or when we were conducting the experiment at a recessed storefront outdoor patio. Transient levels could actually exceed 1,000 micrograms at the closest positions. For reference, the EPA standard for particles in outdoor air is only 35 micrograms (24-hour average).
However, it is important to stress that measurable exposure also occurred at further distances. When a real smoker was present, rather than just smoldering cigarettes, or when we monitored at a position consistently downwind from a smoldering cigarette, we measured elevated average pollution levels even at 9 to 12 feet away from the active cigarette. Thus, EVEN IF A PERSON WERE SEATED 1 OR 2 TABLES REMOVED FROM A SINGLE SMOKER, THEY COULD STILL RECEIVE APPRECIABLE EXPOSURE TO OUTDOOR TOBACCO SMOKE.
We found an approximate theoretical relationship between exposure and the distance from a burning cigarette: As a person moves a given distance away from an active cigarette, the average pollution levels tend to drop off in equal proportion to this change in distance. For example, if a person moves from 1 foot to 10 feet away from a cigarette, which is a distance 10 times further away, the levels would be expected to drop off by a factor of approximately 10.