Objective To assess secondhand smoke (SHS) exposure in Thai international airports using a fine particulate indicator, particulate matter ≤2.5 μm (PM_2.5), and to compare with 2012 exposure findings in international airports in the USA.

Methods Smoking rooms in the four largest international airports that serve the most travellers and with the most operating designated smoking rooms (DSRs) were monitored using PM_2.5 monitoring equipment following an approved research protocol for assessing fine particle pollution from tobacco smoke. Monitoring was conducted inside and just outside DSRs and throughout the airport terminals in all four airports. Altogether 104 samples were taken to assess SHS exposure in four airports. Simultaneous samples were taken multiple times in a total of 11 DSRs available for sampling in the research period.

Results Levels of PM_2.5 in DSRs were extremely high in all four airports and were more dangerous inside DSRs than in the US airports (overall mean=532.5 vs 188.7 µg/m³), higher outside DSRs than in the US airports (overall mean=50.1 vs 43.7 µg/m³), and at comparable levels with the US airports in the terminals away from DSRs (overall mean=13.8 vs 11.5 µg/m³. Findings show that travellers and employees in or near DSRs in the airports assessed in Thailand are being exposed to even higher levels of SHS than in US airports that still have DSRs.

Conclusions Extremely high levels of SHS in and adjacent to DSR show that these rooms are not providing safe air quality for employees and travellers. These high levels of exposure are above those levels reported in US airports and show the need for remedial action to ensure safe air quality in international airports in Thailand.