Indoor air pollutant exposure and determinant factors controlling household air quality for elderly people in Hong Kong

This study investigated the levels and determinant factors of indoor air pollutants including fine particles (PM_2.5), nitrogen dioxide (NO₂), and formaldehyde (HCHO) in 55 households exclusively for the elderly in Hong Kong during summer and winter (Jul.–Sep. 2016 and Nov. 2016–Mar. 2017). The average concentrations of PM_2.5, NO₂, and formaldehyde were 25.3 ± 15.0, 40.5 ± 16.0, and 26.1 ± 22.8 μg/m³ in summer and 34.2 ± 19.0, 43.5 ± 17.0, and 15.4 ± 4.5 μg/m³ in winter, respectively. There were ~ 50.3% of households exceeding the World Health Organization indoor air quality standard for PM_2.5 throughout the study, with ~ 40.6 and ~61.0% of the households in summer and winter, respectively. The determinant factors for indoor PM_2.5 and NO₂ concentrations were identified as from incense burning and cooking. Cooking with suitable ventilation is an important factor to ease indoor pollutant concentrations. Both of PM_2.5 and NO₂ indoor concentrations showed good correlations with outdoor concentrations. Winter was observed with higher pollutant concentrations than summer except for formaldehyde concentrations. Major factors controlling indoor formaldehyde concentrations are temperature and humidity. The outcome will be useful for the development of future indoor air quality guidelines for Hong Kong.