Effects of airing behaviours on bedroom air pollutants during sleep

Higher ventilation rates were verified to have a positive impact on indoor air quality and therefore benefit sleep quality. However, how does ventilation influence bedroom air quality if the outdoor air quality is poor? Whilst ventilation helps to reduce indoor pollution it inadvertently brings outdoor pollution indoors, such as NO₂, which is from vehicular emission. In this study, we collected the info of window and door status during sleep and measured carbon dioxide (CO₂), nitrogen dioxide (NO₂), volatile organic compounds (VOCs) and particulate matter (PM_2.5 and PM₁₀) among 38 bedrooms while occupants were sleeping during nights. Meanwhile, the air change rate (ACR) was calculated. The experiments were conducted in the heating season (September to December 2020) in the capital region of Denmark. The median values were 981.8 ppm (mean CO₂ level during sleep), 0.6 h^-1 (ACR), 3.4 µg·m⁻³ (NO₂), 166.2 µg·m⁻³ (VOCs), 11.0 µg·m^-3 (PM₁₀) and 2.8 µg·m^-3 (PM_2.5). CO₂ levels were positively correlated with VOCs levels, whereas negatively correlated with NO₂ levels in bedrooms. ACR was also negatively correlated with VOCs. CO₂ levels were significantly higher whereas NO₂ levels were lower with both window and door closed compared to them with either window or door open. With higher ventilation rates, while occupants would be less exposed to indoor pollution of VOCs, they would be increasingly exposed to NO₂. Future studies of bedroom ventilation and sleep quality should consider outdoor air quality.