Objective Using data on fine particulate matter less than 2.5 μm (PM_2.5) concentrations in smoking and non-smoking homes in Scotland to estimate the mass of PM_2.5 inhaled by different age groups.

Methods Data from four linked studies, with real-time measurements of PM_2.5 in homes, were combined with data on typical breathing rates and time-activity patterns. Monte Carlo modelling was used to estimate daily PM_2.5 intake, the percentage of total PM_2.5 inhaled within the home environment and the percentage reduction in daily intake that could be achieved by switching to a smoke-free home.

Results Median (IQR) PM_2.5 concentrations from 93 smoking homes were 31 (10–111) μg/m³ and 3 (2–6.5) μg/m³ for the 17 non-smoking homes. Non-smokers living with smokers typically have average PM_2.5 exposure levels more than three times higher than the WHO guidance for annual exposure to PM_2.5 (10 μg/m³).

Conclusions Fine particulate pollution in Scottish homes where smoking is permitted is approximately 10 times higher than in non-smoking homes. Taken over a lifetime many non-smokers living with a smoker inhale a similar mass of PM_2.5 as a non-smoker living in a heavily polluted city such as Beijing. Most non-smokers living in smoking households would experience reductions of over 70% in their daily inhaled PM_2.5 intake if their home became smoke-free. The reduction is likely to be greatest for the very young and for older members of the population because they typically spend more time at home.