Background/Objectives To describe secondhand smoke (SHS) levels in halls and main entrances (outdoors) in different buildings by measurement of PM_2.5 and airborne nicotine.

Methods Cross-sectional study in a sample of 47 public buildings. The authors studied SHS levels derived from PM_2.5 (micrograms per cubic metre) using TSI SidePak Personal Aerosol Monitors. The authors tested four locations within buildings: hall, main entrance (outdoor), control (indoor) and control (outdoor). The authors also measured airborne nicotine concentration (micrograms per cubic metre) in main entrances (outdoor). The authors computed medians and IQRs to describe the data. Spearman correlation coefficient (rsp) was used to explore the association between PM_2.5 concentrations simultaneously measured in halls and main entrances as well as between PM_2.5 and nicotine concentrations.

Results The authors obtained an overall median PM_2.5 concentration of hall 18.20 μg/m³ (IQR: 10.92–23.92 μg/m³), main entrance (outdoor) 17.16 μg/m³ (IQR: 10.92–24.96 μg/m³), control (indoor) 10.40 μg/m³ (IQR: 6.76–15.60 μg/m³) and control (outdoor) 13.00 μg/m³ (IQR: 8.32–18.72 μg/m³). The PM_2.5 concentration in halls was more correlated with concentration in the main entrances (outdoors) (rsp=0.518, 95% CI 0.271 to 0.701) than with the control indoor (rsp=0.316, 95% CI 0.032 to 0.553). The Spearman correlation coefficient between nicotine and PM_2.5 concentration was 0.365 (95% CI −0.009 to 0.650).

Conclusions Indoor locations where smoking is banned are not completely free from SHS with levels similar to those obtained in the immediate entrances (outdoors) where smoking is allowed, indicating that SHS from outdoors settings drifts to adjacent indoors. These results warrant a revision of current smoke-free policies in particular outdoor settings.