Indoor PM2.5 concentrations during winter in a severe cold region of China: A comparison of passive and conventional residential buildings

Severe haze episodes characterized by fine particles have occurred frequently in severe cold areas of China during the winter, which poses a serious health concern to humans. Currently, there is an increasing trend in China to build energy efficient passive houses that are capable of tolerating poor outdoor air pollution with tighter envelopes etc. This study aims to investigate the characteristics of indoor PM2.5 in the first passive residential building in Harbin and to compare them with those of a conventional building, considering different outdoor air qualities. The measurements and modeling of indoor PM2.5 were conducted in passive households (PHs) and conventional households (CHs). The air change rates were also quantitatively studied using the carbon dioxide (CO₂) gas decay method and the supply airflow rate method. The results indicated that the residents of a severely polluted city had high health risks associated with exposure to PM2.5 that exceeded daily limits of 25 μg/m³. PHs could increase the acceptable time (≤75 μg/m³) ratios compared to CHs, under the limitation of heavy outdoor pollution owing to low filter efficiency. With a portable air cleaner, the CHs could reduce the PM2.5 exposure considerably; however, the ventilation rate may be insufficient. Regression analyses demonstrated that the PHs had a higher infiltration factor than the CHs, owing to the higher ventilation rate and insufficient filtration efficiency. To simultaneously obtain sufficient fresh air and maintain the PM2.5 concentrations below the guideline, mechanical ventilation with improved filtration efficiency is warranted; alternatively, a portable air cleaner is desirable.