“…These indoor sources may be associated with specific frequent activities carried out by dwellers, such as cooking [15,16], cleaning [17], candle burning [18], home heating [19][20][21][22], vacuuming [15], and other activities, which increase pollutants above acceptable indoor levels. A wide range of pollutants can originate via these activities including particulate matter (PM 2.5 , PM 10 ) [23], ultrafine particles (UFP) [15,24], volatile organic compounds (VOCs) [25,26], carbon dioxide [19], carbon monoxide [19,22], formaldehyde [19], polycyclic aromatic hydrocarbons [16,27], among others. For instance, cooking was found to increase PM levels by four times the background levels in a study at 14 naturally ventilated homes of Hong Kong [28].…”