Estimating population exposure to ambient polycyclic aromatic hydrocarbon in the United States – Part I: Model development and evaluation

Abstract

PAHs (polycyclic aromatic hydrocarbons) in the environment are of significant concern due to their negative impact on human health. PAH measurements at the air toxics monitoring network stations alone are not sufficient to provide a complete picture of ambient PAH levels or to allow accurate assessment of public exposure in the United States. In this study, speciation profiles for PAHs were prepared using data assembled from existing emission profile data bases, and the Sparse Matrix Operator Kernel Emissions (SMOKE) model was used to generate the gridded national emissions of 16 priority PAHs in the US. The estimated emissions were applied to simulate ambient concentration of PAHs for January, April, July and October 2011, using a modified Community Multiscale Air Quality (CMAQ) model (v5.0.1) that treats the gas and particle phase partitioning of PAHs and their reactions in the gas phase and on particle surface. Predicted daily PAH concentrations at 61 air toxics monitoring sites generally agreed with observations, and averaging the predictions over a month reduced the overall error. The best model performance was obtained at rural sites, with an average mean fractional bias (MFB) of −0.03 and mean fractional error (MFE) of 0.70. Concentrations at suburban and urban sites were underestimated with overall MFB = −0.57 and MFE = 0.89. Predicted PAH concentrations were highest in January with better model performance (MFB = 0.12, MFE = 0.69; including all sites), and lowest in July with worse model performance (MFB = −0.90, MFE = 1.08). Including heterogeneous reactions of several PAHs with O3 on particle surface reduced the over-prediction bias in winter, although significant uncertainties were expected due to relative simple treatment of the heterogeneous reactions in the current model.

Estimating population exposure to ambient polycyclic aromatic hydrocarbon in the United States – Part II: Source apportionment and cancer risk assessment

“…A complete list of the 16 PAHs and the kinetics and equilibrium parameters are listed in Table 2 of Zhang et al (2016).…”

“…Details of the gas phase reaction, gas-to-particle partitioning and heterogeneous reactions of the PAHs have been discussed in detail in Zhang et al (2016) and a short summary is provided below. The gas phase reaction mechanism SAPRC-99 (Carter, 2003) was expanded to include reactions of PAHs with hydroxyl radical (OH) and ozone (O 3 ).…”

“…Details of the model setup and input data preparation can be found in Part I of the paper series (Zhang et al, 2016) and only a short summary is provided below. The model domain used in this study is 36 × 36 km 2 in horizontal resolution with 18 stretching vertical layers that reach a model top of approximately 20 km above surface.…”

“…Occupational and environmental exposure to polycyclic aromatic hydrocarbons (PAH) has also been related with higher human cancer risks in epidemiological studies (Boffetta et al, 1997). The United States Environmental Protection Agency (US EPA) has classified 16 of the PAHs as priority pollutants and designated seven of the PAHs possible human carcinogens (see Table 1 of Zhang et al (2016)). To properly evaluate the level of population exposure and cancer risk due to PAHs, the spatial and temporal distribution of ambient PAHs need to be determined.…”

How much does traffic contribute to benzene and polycyclic aromatic hydrocarbon air pollution? Results from a high-resolution North American air quality model centred on Toronto, Canada

“…Emissions from motor vehicles have been linked to air quality degradation (e.g., WHO, 2005;Han and Naeher, 2006;Zhang and Batterman, 2013;Farrell et al, 2016;Zimmerman et al, 2016;Gentner et al, 2017;Wang et al, 2017) and greenhouse gas pollution (e.g., Sims et al, 2014;Zimmerman et al, 2016;Boulton, 2016;US EPA, 2002) globally. In North America, vehicle emission controls have gradually reduced emissions of many pollutants and made vehicles more fuel efficient (U.S. Environmental Protection Agency, 2012;Reid and Aherne, 2016), with transportation policies being closely aligned in Canada and the United States (ECCC, 2019b).…”