Secondhand tobacco smoke exposure in open and semi-open settings: a systematic review

Abstract

Background: Some countries have recently extended smoke-free policies to particular outdoor settings; however, there is controversy regarding whether this is scientifically and ethically justifiable.

Objectives: The objective of the present study was to review research on secondhand smoke (SHS) exposure in outdoor settings.

Data sources: We conducted different searches in PubMed for the period prior to September 2012. We checked the references of the identified papers, and conducted a similar search in Google Scholar.

Study selection: Our search terms included combinations of "secondhand smoke," "environmental tobacco smoke," "passive smoking" OR "tobacco smoke pollution" AND "outdoors" AND "PM" (particulate matter), "PM(2.5)" (PM with diameter ≤ 2.5 µm), "respirable suspended particles," "particulate matter," "nicotine," "CO" (carbon monoxide), "cotinine," "marker," "biomarker" OR "airborne marker." In total, 18 articles and reports met the inclusion criteria.

Results: Almost all studies used PM(2.5) concentration as an SHS marker. Mean PM(2.5) concentrations reported for outdoor smoking areas when smokers were present ranged from 8.32 to 124 µg/m(3) at hospitality venues, and 4.60 to 17.80 µg/m(3) at other locations. Mean PM(2.5) concentrations in smoke-free indoor settings near outdoor smoking areas ranged from 4 to 120.51 µg/m(3). SHS levels increased when smokers were present, and outdoor and indoor SHS levels were related. Most studies reported a positive association between SHS measures and smoker density, enclosure of outdoor locations, wind conditions, and proximity to smokers.

Conclusions: The available evidence indicates high SHS levels at some outdoor smoking areas and at adjacent smoke-free indoor areas. Further research and standardization of methodology is needed to determine whether smoke-free legislation should be extended to outdoor settings.

Figure 1

Flow diagram for the identification and selection of studies included in the review.

Figure 2

Outdoor PM_2.5 concentrations reported for hospitality venues and other settings according to the presence or absence of smokers. Klepleis et al. (2007) included hospitality and non-hospitality venues without distinguishing the mean value between them, and hence it has been included both in “hospitality venues” and “other venues.” Wilson et al. (2011) and Edwards and Wilson (2011) provided the individual values for each measurement, and we have computed the arithmetic mean for the figure. Brennan et al. (2010) and López et al. (2012) provided mean and median values, respectively, for venues before and after a smoking ban. We have computed the average values for each study to include them in the figure.