Introducing a partitioning mechanism for PAHs into the Community Multiscale Air Quality modeling system and its application to simulating the transport of benzo(a) pyrene over Europe

Into the Community Multiscale Air Quality modeling system (CMAQ) that is widely used for simulating the transport and fate of air pollutants, a new module was inserted that accounts for the partitioning of semivolatile organic compounds-in particular, polycyclic organic hydrocarbons (PAHs)-between the gaseous and the particulate phases. This PAH version of CMAQ can at this time be applied to substances that are predominantly associated with particles and can be assumed to be inert, as is the case for benzo(a) pyrene [B(a) P]. The model was set up for Europe on a grid with 54-km cell width with a nest of 18-km gridcell width located around the North Sea to simulate ambient air concentrations and depositions of B(a) P in January, April, July, and October 2000. To evaluate the quality of the simulation results, daily and monthly mean concentrations were compared with measurements from six monitoring stations. The typical ratio of modeled to measured values is circa 4 (median), which-with respect to both measurement and simulation uncertainties and problems involved when comparing measurements with simulations-proved that the PAH version of CMAQ is suitable to simulate the fate and transport of B(a) P over Europe and can serve as a starting point for models for other PAHs that additionally consider degradation.