Abstract
In order to identify the sources of indoor PM2.5 and to check which factors influence the concentration of indoor PM2.5 and chemical elements, indoor concentrations of PM2.5 and its related elements in residential houses in Beijing were explored. Indoor and outdoor PM2.5 samples that were monitored continuously for one week were collected. Indoor and outdoor concentrations of PM2.5 and 15 elements (Al, As, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Pb, Se, Tl, V, Zn) were calculated and compared. The median indoor concentration of PM2.5 was 57.64 μg/m3. For elements in indoor PM2.5, Cd and As may be sensitive to indoor smoking, Zn, Ca and Al may be related to indoor sources other than smoking, Pb, V and Se may mainly come from outdoor. Five factors were extracted for indoor PM2.5 by factor analysis, explained 76.8% of total variance, outdoor sources contributed more than indoor sources. Multiple linear regression analysis for indoor PM2.5, Cd and Pb was performed. Indoor PM2.5 was influenced by factors including outdoor PM2.5, smoking during sampling, outdoor temperature and time of air conditioner use. Indoor Cd was affected by factors including smoking during sampling, outdoor Cd and building age. Indoor Pb concentration was associated with factors including outdoor Pb and time of window open per day, building age and RH. In conclusion, indoor PM2.5 mainly comes from outdoor sources, and the contributions of indoor sources also cannot be ignored. Factors associated indoor and outdoor air exchange can influence the concentrations of indoor PM2.5 and its constituents.
Highlights
The majority of adults spend more than 80% of the day in a variety of indoor environments, mainly in their houses [1,2,3]
After excluding the failed samples caused by filter damage and invalid flow rates, 47 houses in non-heating season (NHS) and 47 houses in heating season (HS) were left for further analysis
Outdoor PM2.5 concentration in heating season was much higher than in non-heating season in this study, a seasonal difference that has been reported in several other studies conducted in Beijing [30,53,77,78], but not consistent with the study conducted in Beijing by Han [60] which may due to the short sampling periods and the frequent and rapid transition between severe pollution events and clean days
Summary
The majority of adults spend more than 80% of the day in a variety of indoor environments, mainly in their houses [1,2,3]. The contribution of indoor air is very important for accurate estimation of individual air pollution exposure. The PM2.5 exposure assessment in most of these studies is usually based on ambient PM2.5 data, regardless of the difference between indoor and outdoor. Failure to account for the contribution of indoor PM2.5 concentration may lead to exposure misclassifications, which have become source of measurement bias in the PM2.5 epidemiologic studies linking health effects to PM2.5 exposure [11,12,13,14]. Outdoor PM2.5 typically comes from sources such as fossil fuels combustion, motor vehicle exhaust, industrial emissions, soil and dust, and particles from these sources can penetrate into indoor through building gap, door, window and mechanical ventilation [12,15,16,17,18]. A survey conducted in Beijing showed that 54–63% of indoor PM2.5
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