Model-based approach to account for the variation of primary VOC emissions over time in the identification of indoor VOC sources

The study objectives were to improve the understanding of the long-term variation of VOC emission chromatograms of building materials and to develop a method to account for this variation in the identification of individual sources of VOC emissions. This is of importance for the application of the source identification method since materials age over time in real indoor environments. The method is based on the mixed air sample measurements containing pollutants from multiple aged materials and the emission signatures of individual new materials determined by PTR-MS. Three emission decay source models were employed and evaluated for their ability to track the change of individual material emission signatures by PTR-MS over a nine-month period. Nine building material specimens were studied in a ventilated 50-L small-size chamber for their emissions individually for nine months, and also in combination later. Chamber exhaust air was sampled by PTR-MS to construct a temporal profile of emission signature unique to individual product type. The similar process was taken to measure mixture emissions from multiple materials, which is for applying and validating the developed method for source identification enhancement, considering the variation in long-term emission rates of individual VOCs. Results showed that the proposed approach could predict the emission signatures of individual building materials at a later time (9-month) with less than 6% difference variance, and hence indicated the potential of the source identification method for aged materials in real indoor environments.