Restrictions on smoking outdoors have been introduced for reasons of public amenity and to promote litter reduction. This review considers the evidence about whether outdoor secondhand smoke (SHS) might also pose health risks to others. Six published studies have assessed outdoor levels of SHS using metred PM2.5 as a marker of exposure. The magnitude of PM2.5is dependent on the number of smokers present, proximity of the measurement device to the source of the SHS, the extent to which the outdoor space is physically constrained (e.g., walls, partial roof, umbrellas), and wind. The data show peak outdoor PM2.5 levels in semi-enclosed areas with several smokers present can be comparable to those recorded in indoor smoky environments. However, outdoor PM2.5 levels are more transient as the smoke plume is less confined and can rapidly dissipate. SHS can be a major source of PM2.5, particularly in indoor environments. The average PM2.5 level in bars where smoking occurs is 303 µg/m3 and 157 µg/m3 in restaurants. Because of repeated and cumulative exposure to SHS in outdoor settings like beer gardens and outdoor eating areas, occupational exposures to PM2.5 from SHS are likely to be far higher than those experienced by patrons who are present for far shorter periods. We estimate that occupational exposure to SHS in waitstaff working in outdoor patio areas where smoking is allowed could average 1.6 to 9.8 µg/m3 per year. It is thus plausible that occupational exposure to PM2.5 in outdoor work settings where smoking is allowed could exceed the Australian National Environment Protection Measure for Ambient Air Quality benchmark annual average target of 8µg/m3 . An increase of 5µg/m3 to 10 µg/m3 in average annual PM2.5 exposure is associated with a 3-6% increase in all-cause mortality. Personal monitoring studies have not yet been conducted to corroborate modelled estimates of staff exposure in these settings. Such studies should be conducted to test the modelled exposure estimates we have calculated.The Sax Institut
