Abstract
Abstract. The offline Eulerian AURAMS (A Unified Regional Air quality Modelling System) chemical transport model was adapted to simulate airborne concentrations of seven PAHs (polycyclic aromatic hydrocarbons): phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene + triphenylene, and benzo[a]pyrene. The model was then run for the year 2002 with hourly output on a grid covering southern Canada and the continental USA with 42 km horizontal grid spacing. Model predictions were compared to ~5000 24 h-average PAH measurements from 45 sites, most of which were located in urban or industrial areas. Eight of the measurement sites also provided data on particle/gas partitioning which had been modelled using two alternative schemes. This is the first known regional modelling study for PAHs over a North American domain and the first modelling study at any scale to compare alternative particle/gas partitioning schemes against paired field measurements. The goal of the study was to provide output concentration maps of use to assessing human inhalation exposure to PAHs in ambient air. Annual average modelled total (gas + particle) concentrations were statistically indistinguishable from measured values for fluoranthene, pyrene and benz[a]anthracene whereas the model underestimated concentrations of phenanthrene, anthracene and chrysene + triphenylene. Significance for benzo[a]pyrene performance was close to the statistical threshold and depended on the particle/gas partitioning scheme employed. On a day-to-day basis, the model simulated total PAH concentrations to the correct order of magnitude the majority of the time. The model showed seasonal differences in prediction quality for volatile species which suggests that a missing emission source such as air–surface exchange should be included in future versions. Model performance differed substantially between measurement locations and the limited available evidence suggests that the model's spatial resolution was too coarse to capture the distribution of concentrations in densely populated areas. A more detailed analysis of the factors influencing modelled particle/gas partitioning is warranted based on the findings in this study.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous air pollutants that tend to be most concentrated in areas of dense human population (Hafner et al, 2005) but are detected at locations remote from local sources (Hung et al, 2005)
This study presents the results of a chemical transport model, AURAMS (A Unified Regional Air quality Modelling System)-PAH, run over North America at 42 km horizontal grid spacing with hourly output for the year 2002
A modified version of the AURAMS chemical transport models (CTMs) known as AURAMS-PAH was developed to incorporate primary semivolatile organic compounds that are subject to sorptive partitioning
Summary
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous air pollutants that tend to be most concentrated in areas of dense human population (Hafner et al, 2005) but are detected at locations remote from local sources (Hung et al, 2005). Many PAH species have been classified as carcinogens (IARC, 2010) and they are implicated routinely as toxicants in airborne particulate matter (Kelly and Fussell, 2012). They are regulated under international agreements such as the Aarhus Protocol on Persistent Organic Pollutants. Benzo[a]pyrene, a commonly reported PAH species, is subject to ambient air guidelines in many jurisdictions. Galarneau et al.: PAH concentrations simulated with the AURAMS-PAH chemical transport model
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