A new study published this month in the Journal of the Air Waste Management Association examines levels of particulate matter due to cigarette smoke in a variety of outdoor locations under various circumstances (see: Klepeis NE, Ott WR, Switzer P. Real-time measurement of outdoor tobacco smoke particles. Journal of the Air Waste Management Association 2007; 57: 522-534).
According to the study abstract: "The overall average OTS [outdoor tobacco smoke] respirable particle concentration for the surveys of public places during smoking was approximately 30 ug/m3. OTS exhibited sharp spikes in particle mass concentration during smoking that sometimes exceeded 1000 ug/m3 at distances within 0.5 m of the source. Some average concentrations over the duration of a cigarette and within 0.5 m exceeded 200 ug/m3, with some average downwind levels exceeding 500 ug/m3. OTS levels in a constant upwind direction from an active cigarette source were nearly zero. OTS levels also approached zero at distances greater than approximately 2 m from a single cigarette. During periods of active smoking, peak and average OTS levels near smokers rivaled indoor tobacco smoke concentrations. However, OTS levels dropped almost instantly after smoking activity ceased. Based on our results, it is possible for OTS to present a nuisance or hazard under certain conditions of wind and smoker proximity."
The basic finding of the study is that if you are within a few feet of a smoker in an outdoors location, your exposure to secondhand smoke can be quite high, approximating that of indoor exposure under relatively smoky conditions. On the other hand, once you get beyond about 6 feet from the smoker, the exposure is minimal.
The authors conclude: "OTS [outdoor tobacco smoke] levels are highly dependent on source proximity. Levels at 0.25–0.5 m can drop by half or more as the distance increases to 1–2 m. At distances >2 m, levels near single cigarettes were generally close to background."
The Rest of the Story
While the results of this study are likely to be used by some anti-smoking groups to try to justify on health grounds widespread bans on outdoor smoking, even in places where nonsmokers can freely move about - like sidewalks, streets, parking lots, and parks - the rest of the story is that the study actually demonstrates that there is little health justification for banning smoking outdoors except in locations where nonsmokers are not easily able to move away from smokers.
For example, the findings justify smoking bans in locations where nonsmokers are in fixed seating - such as an outdoor stadium. In such situations, a nonsmoker could be within 6 feet of a smoker and unable to move away, due to the fixed seating. Secondhand smoke exposure could be considerably high, justifying a smoking ban on health grounds.
However, the findings demonstrate the lack of a health justification for more widespread bans on outdoor smoking, such as the ban recently enacted in Calabasas, where smoking is prohibited in just about any outdoor location, such as streets, sidewalks, parking lots, and parks. In such situations, the study documents that nonsmokers can easily avoid substantial exposure to secondhand smoke simply by walking away from the smoker(s). At a distance of 6 feet or greater, exposure becomes minimal.
This study appears to confirm the validity of the criterion I have previously suggested be used to judge the health justification of smoking bans: are nonsmokers easily able to avoid the smoke by moving away from smokers? If the answer is no, then an outdoor smoking ban in that venue is justified. Of the answer is yes, then it is unlikely that an outdoor smoking ban in that situation is justified on health grounds.
Will the results of this study cause anti-smoking groups to reassess their support for widespread outdoor smoking bans in places where nonsmokers can avoid proximity to smokers? I highly doubt it. Why? Because as I have learned, this is no longer about the science. It is about the agenda. We no longer need the science to justify our agenda. As this movement has largely become a crusade, rather than a reasonable, evidence-based practice of public health, we no longer need scientific or health justification for our actions and policies.
Now that the tobacco industry has largely decided to discontinue its opposition to smoking bans, there is nothing left that requires us to justify our policies on health and science grounds - perhaps with the exception of some guy's tobacco policy blog.
The bottom line is that secondhand smoke outdoors poses no substantial health threat to nonsmokers unless they are not easily able to avoid proximity of less than about 6 feet from any smoker. The distance required to avoid substantial exposure may be somewhat higher for a group of smokers. If nonsmokers want to avoid exposure to secondhand smoke outdoors in such situations, they can just walk away. It is only in situations where walking away is not an option (such as waiting tables in an outdoor cafe or sitting in a stadium with fixed seating) that regulation of outdoor smoking is justified on health grounds.