Continuous in-situ measurements of HCHO and other VOCs by PTR-MS in nine homes in eastern WA
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Exposure of volatile organic compounds (VOCs) can have negative impacts on human health but the range of indoor levels, along with variations and relationship with influencing factors are poorly understood. In this dissertation, the measurements of indoor and outdoor levels of formaldehyde and other pollutants, and influencing factors including temperature and air change rate (ACH) in nine single-family homes in eastern Washington State were presented. Proton transfer reaction mass spectrometer (PTR-MS) was applied to track the variation of indoor VOC levels. The results showed that for homes where infiltration dominated the ACH, the indoor VOC levels showed a diurnal variation, which suggests that the steady-state assumption regarding whole house emissions may not be applicable. For most homes measured, indoor formaldehyde levels ranged from 8 to 44 ppbv. Summertime indoor formaldehyde levels measured in homes with only infiltration as ACH displayed a linear increase with indoor temperature and the slopes ranged from 3.0 ppbv per °C to 4.5 ppbv per °C, and this increase results from the interaction of whole house emissions sensitivity to temperature and the impact of indoor temperature on infiltration rates. The data measured in a net-zero energy house were analyzed to examine the levels and trends of VOCs under multiple ventilation settings. For indoor temperatures of approximately 25 oC, formaldehyde decay coefficient was determined to be 0.50 ± 0.09 hr-1 and its emission rates were determined to be 90 ± 10 μg m-2 hr-1 under 0.49 hr-1 ACH, compared to 81 ± 16 μg m-2 hr-1 at natural infiltration rates estimated as 0.05 hr-1. The results showed only a 10% difference in emission rates observed for formaldehyde at these two very different ACHs. Our time-dependent mass balance model showed that this lack of sensitivity to ACH is due to the relatively large decay coefficient for formaldehyde. In comparison, for other VOCs, the whole house emission rates increased by a factor up to 3 when ACH increased from 0.05 hr-1 to 0.49 hr-1. For these VOCs, the decay coefficients are near zero so that the emission rates are much more dependent upon ACH.