Secondhand smoke exposure (PM2.5) in outdoor dining areas and its correlates

Background This study assessed the magnitude of secondhand smoke (SHS) exposure when people smoke in outdoor dining areas and explored conditions influencing exposure levels. Methods Data were gathered from 69 outdoor dining areas in Melbourne, Australia, during April/May 2007. Sitting at tables within 1 metre of an active smoker, the authors measured the concentration of particulate pollution (PM2.5) using TSI SidePak Personal Aerosol Monitors. PM2.5 data were recorded by the monitor at 30-second intervals, and data were collected over an average of 25.8 minutes per venue. Information was collected about the presence of overhead coverings and the number of patrons and lit cigarettes. Results The average background level of PM2.5 was 8.4 mg/m(3) (geometric mean (GM) 6.1 mg/m(3)), increasing to an average of 17.6 mg/m(3) (GM 12.7 mg/m(3)) over the observational period and 27.3 mg/m(3) (GM 17.6 mg/m(3)) during the time that cigarettes were actively smoked near the monitor. There was substantial variation in exposure levels, with a maximum peak concentration of 483.9 mg/m(3) when there were lit cigarettes close to the monitor. Average exposure levels increased by around 30% for every additional active smoker within 1 metre of the monitor. Being situated under an overhead cover increased average exposure by around 50%. Conclusions When individuals sit in outdoor dining venues where smokers are present it is possible that they will be exposed to substantial SHS levels. Significant increases in exposure were observed when monitors were located under overhead covers, and as the number of nearby smokers increased. The role of outdoor smoking restrictions in minimising exposure to SHS must be considered.