Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/gmd-2017-324
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Development and technical paper
31 Jan 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).
GEM-MACH-PAH (rev2488): a new high-resolution chemical transport model for North American PAHs and benzene
Cynthia H. Whaley1,2, Elisabeth Galarneau1, Paul A. Makar1, Ayodeji Akingunola1, Wanmin Gong1, Sylvie Gravel1, Michael D. Moran1, Craig Stroud1, Junhua Zhang1, and Qiong Zheng1 1Air Quality Research Division, Environment and Climate Change Canada, 4905 Dufferin Street, Toronto, ON, M3H 5T4, Canada
2Climate Research Division, Environment and Climate Change Canada, 4905 Dufferin Street, Toronto, ON, M3H 5T4, Canada
Abstract. Environment and Climate Change Canada’s online air quality forecasting model, GEMMACH, was extended to simulate atmospheric concentrations of benzene and seven polycyclic aromatic hydrocarbons (PAHs): phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene, chrysene, and benzo(a)pyrene (BaP). In the expanded model, benzene and PAHs are emitted from major point, area, and mobile sources, with emissions based on recent emission factors. Modelled PAHs undergo gas-particle partitioning (whereas benzene is only in the gas phase), atmospheric transport, oxidation, cloud processing, and dry and wet deposition. To represent PAH gas-particle partitioning, the Dachs-Eisenreich scheme was used, and we have improved gas-particle partitioning parameters based on an empirical analysis to get significantly better gas-particle partitioning results than the previous North American PAH model, AURAMS-PAH. Other added process parameterizations include the particle phase benzo(a)pyrene reaction with ozone via the Kwamena scheme and gas-phase scavenging of PAHs by snow via vapor sorption to the snow surface.

The resulting GEM-MACH-PAH model was used to generate the first online model simulations of PAH emissions, transport, chemical transformation and deposition for a high resolution domain (2.5-km grid cell spacing) in North America, centered on the PAH-data-rich region of southern Ontario, Canada and the north-eastern United States. Model output for two seasons was compared to measurements from three monitoring networks spanning Canada and the U.S. Average summertime model results were found to be statistically indistinguishable from measurements of benzene and all seven PAHs. The same was true for the winter seasonal mean, except for BaP, which had a statistically significant positive bias.We present evidence that the benzo(a)pyrene results may be ameliorated via further improvements to PM and oxidant processes and transport. Our analysis focused on four key components to the prediction of atmospheric PAH levels: spatial variability; sensitivity to mobile emissions; gas-particle partitioning; and wet deposition. Spatial variability of PAHs/PM2.5 at 2.5-km resolution was found to be comparable to measurements. Predicted ambient surface concentrations of benzene and the PAHs were found to be critically dependent on mobile emission factors, indicating the mobile emissions sector has a significant influence on ambient PAH levels in the study region. PAH wet deposition was overestimated due to additive precipitation biases in the model and the measurements. Our overall performance evaluation suggests that GEM-MACHPAH can provide seasonal estimates for benzene and PAHs and be suitable for emissions scenario simulations.


Citation: Whaley, C. H., Galarneau, E., Makar, P. A., Akingunola, A., Gong, W., Gravel, S., Moran, M. D., Stroud, C., Zhang, J., and Zheng, Q.: GEM-MACH-PAH (rev2488): a new high-resolution chemical transport model for North American PAHs and benzene, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2017-324, in review, 2018.
Cynthia H. Whaley et al.
Cynthia H. Whaley et al.

Model code and software

GEM-MACH-PAH rev2488 C. H. Whaley, E. Galarneau, P. A. Makar, M. Moran, C. Stroud, and W. Gong https://doi.org/10.5281/zenodo.1162252
Cynthia H. Whaley et al.

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Short summary
We present a new, high-resolution, North American model of PAHs and benzene, which are toxic air pollutants that cause a variety of health impacts. Our simulation in a densely populated region of Canada and the U.S. shows that the model is improved over a previous model, particularly for the gas-particle partitioning of these pollutants, which has impacts on deposition and inhalation. The simulation was sensitive to the selection of vehicle emissions.
We present a new, high-resolution, North American model of PAHs and benzene, which are toxic air...
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