An increasing number of cities and countries have implemented outdoor smoking restrictions at building entrances. The purpose of this study was to determine outdoor tobacco smoke (OTS) exposure as a function of distance from a smoking source.


Outdoor concentrations of ambient particulate matter smaller than 2.5 μm in aerodynamic diameter (PM2.5) were measured at 4 different distances (1, 3, 6, and 9 m) from a simulated smoking source. Wind speed and direction were measured using a wind meter. In total, 98 experiments were conducted on an outdoor rooftop. The experiments were conducted in 5 days with average wind speed of 0.8±0.6 m/s. One smoking experiment consisted of 13min (5 nonsmoking min, 3 smoking min, and 5 more nonsmoking min). The difference between mean PM2.5 concentrations during smoking and nonsmoking conditions was determined as the OTS exposure.


The OTS levels were 72.7, 11.3, 4.1, and 2.6 µg/m3 at 1, 3, 6, and 9 m, respectively. Although the OTS levels decreased with increasing distance from the smoking source, the OTS levels were significantly higher than zero at all distances. The downwind OTS levels were significantly higher than upwind levels. The OTS levels were negatively associated with wind speed.


The outdoor PM2.5 levels were significantly higher with smoking than without smoking. Because the OTS was detectable even at 9 m with only one cigarette smoking, the minimum distance from a smoking source to prevent OTS exposure should be at least 9 m.

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