PM2.5 concentrations of outdoor tobacco smoke at different distances from the smoking source: Is there an optimal distance for a designated smoking area?

Many countries have enacted indoor smoke-free policies, and some have established outdoor non-smoking areas. However, no clear standard for determining the optimal distance for these outdoor non-smoking zones remains. This study aimed to evaluate outdoor tobacco smoke (OTS) exposure up to a distance of 21 m and to identify factors influencing OTS levels. To assess OTS levels, PM2.5 concentrations were measured at distances of 6, 12, 15, 18, and 21 m using real-time aerosol monitors. Between August and October 2022, a total of 164 measurements were undertaken. The background PM2.5 concentration was gauged for 5 minutes before smoking commenced and then re-measured 3 minutes during smoking. OTS levels were determined by calculating the difference between the average background PM2.5 and the average PM2.5 concentrations during smoking. A one-sample t-test was employed to ascertain if the OTS levels at each distance were significantly elevated compared to 0 µg/m3. Furthermore, a multiple linear regression analysis was conducted to determine the factors influencing OTS levels. The mean OTS levels recorded at all specified distances significantly surpassed 0 µg/m3. The regression analysis revealed that the OTS levels correlated significantly with distance and wind speed. Specifically, OTS levels diminished as distance expanded and wind speed reduced. OTS levels, even at 21 m, were significantly greater than 0 µg/m3. Our results provide robust evidence supporting the establishment of outdoor non-smoking zone up to 21 m. Outdoor tobacco smoke (OTS) level was determined by PM2.5 concentration. The OTS levels significantly exceeded 0 µg/m3 at every measured distance up to 21 m. In the regression model, OTS levels notably correlated with distance and wind speed. OTS levels diminished as distance expanded and wind speed reduced.

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