The impact of increased occupancy on particulate matter concentrations in mechanically-ventilated residential buildings in a subtropical climate

Indoor air pollution can pose a serious threat to human health and can increase the risk of early mortality. Studies have shown that human exposure to indoor pollution is more common than to outdoor pollution, especially where people spend the majority of their time indoors at home. Heating, ventilating, and air conditioning (HVAC) systems are used in buildings to regulate internal climate to improve the comfort level for occupants. In addition, ventilation rates are often increased to maintain appropriate Indoor Air Quality (IAQ). Inadequate ventilation can limit the removal of substances from inside the building, leading to an accumulation of pollutants resulting from internal sources (e.g., building materials, furnishings, and personal care products). Minimum ventilation rates for buildings are prescribed in standards published by organisations such as the European Committee for Standardization and ASHRAE. However, unlike outdoor air quality, there is currently no common standard or index for IAQ.
The aim of this study is to investigate the impact of high occupancy levels, caused by stay-at-home orders under a COVID-19 lockdown, on IAQ in mechanically-ventilated residential buildings. The study focuses on particulate matter (PM2.5 and PM10) in six residential buildings across Auckland, New Zealand’s largest city, which has a subtropical climate with characteristic high humidity in the winter. Monitoring took place over a six-week period during winter: three weeks pre-COVID-19 lockdown and three weeks into the lockdown.
Indoor concentrations of PM2.5 and PM10 were found to increase during the lockdown period in the majority of the houses (64% and 40% respectively). In contrast, outdoor PM2.5 and PM10 concentrations decreased by 34% and 31%, suggesting internal sources were largely responsible for indoor concentrations.