Development of emission factors for secondary organic aerosol precursors from in-service asphalt roofs using Monte Carlo-based quantitative uncertainty analysis

Several recent studies have examined the role of intermediate/semi-volatile organic compound emissions from paving and roofing asphalts in the formation of secondary organic aerosols (SOAs), which constitute a portion of fine atmospheric particulate matter. These studies have yielded divergent results. Building upon this research, this study aims to develop more representative emission factors for estimating the contribution of roofing materials to SOA formation. This was accomplished by investigating the impact on SOA formation of variables such as rooftop temperatures, solar insolation values, study durations, and the physical and chemical properties of the roofing materials tested. To quantify the influence of these variables, data from existing literature were drawn, and limited experimental lab work was conducted. Monte Carlo-based quantitative uncertainty and sensitivity analyses were completed to estimate more representative emission factors, generate accompanying uncertainty ranges, and rank critical parameters driving emissions that should be considered in any follow-up research. The emission factors developed in this study resulted in a central tendency estimate of 1.7 × 10^-4 Gg/yr SOA for the 720 hottest hours in Southern California, with a 90% confidence interval of 6.0 × 10^-5 to 3.4 × 10^-4 Gg/yr. For the 4,320 annual daylight hours, the central tendency estimate is 2.1 × 10^-5 Gg/yr, with a 90% confidence interval of 4.7 × 10^-6 to 5.1 × 10^-5 Gg/yr. To provide perspective, the results of this study indicate that the SOA contribution to in-service emissions from asphalt roofing surfaces is four to five orders of magnitude lower than that reported for mobile diesel and gasoline sources.