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Formaldehyde has substantial adverse impacts on human health, and formaldehyde exposure primarily occurs in indoor environments. This study investigated the infiltration rates and indoor formaldehyde concentrations in 5 climate zones of China. In the winter, apartments in northern China suffer from higher indoor formaldehyde concentrations than apartments in southern China. The median indoor formaldehyde concentrations were 56 μ g / m 3 (25%, 75%: 38, 91 μ g / m 3 ) in northern China and 40 μ g / m 3 (25%, 75%: 30, 61 μ g / m 3 ) in southern China. There is a clear decrease in indoor formaldehyde concentrations in China. We also studied the relationships of the indoor air temperature, years of decoration, infiltration rate and source characteristic with formaldehyde concentrations in closed conditions. A multiple regression model that related these factors to the formaldehyde concentrations in closed conditions was constructed ( R 2 = 0.75 ). The optimal curve for the suitable combination of temperature and infiltration rate to maintain low formaldehyde concentrations with the lowest cost was calculated for northern and southern China. By comparing the optimal curve and the state point of each city, we can infer the suitable tendency of indoor temperature and infiltration rate for each city. In Tianjin and Shenyang, apartments are overheating, thus causing a high percentage of some homes to have formaldehyde concentrations above the Chinese national standard. In Shanxi, Xinjiang, Yunnan and the Yangtze River Delta, the infiltration rate should be increased to some extent to achieve better indoor air quality. In Hunan, Hubei and Chongqing, indoor temperatures could be increased to improve indoor thermal comfort.

Semi-volatile organic compounds (SVOCs) are widely used in various indoor materials and their adverse health effects have been increasingly recognized. The gas-phase SVOC concentration in equilibrium with the source material ( y 0 ), as a characteristic parameter for SVOC sources, is mostly assumed to be constant in previous studies. However, decreases in y 0 with time have been observed in some studies. As a first step to reveal the mechanism behind the phenomenon, this study quantitatively investigated the variation of y 0 over time under two conditions: natural exposure to outdoor ambient (Case 1), and storage in a controlled ventilated chamber (Case 2). Three phthalates (Di-iso-butyl Phthalate (DiBP), Di-n-butyl Phthalate (DnBP), and di-(2-ethylhexyl) phthalate (DEHP)) emitted from polyvinyl chloride (PVC) floorings and one flame retardant (tris(2-chloroisopropyl) phosphate, TCPP) emitted from polyurethane foam (PUF) were targeted. Experimental results indicated that, for SVOCs with higher volatility, i.e., DiBP, DnBP, and TCPP, y 0 decreased 16%–49% after 60 days' exposure for Case 1; and 16%–36% for Case 2. For SVOCs with lower volatility, i.e., DEHP, no significant decrease in y 0 was observed after 60 days in both cases; while if prolonging the time to about 1.5 years, a decrease of 38% was observed. Discussion about potential reasons for the decrease of y 0 was presented. The results obtained here provide a further understanding about SVOC source characteristics and therefore help providing source strength for estimating indoor SVOC health exposure.