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

Abstract

Into the community multiscale air quality modelling 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 phase. This PAH version of CMAQ can to date be applied to substances that are predominantly associated with particles where they can be assumed to be inert like it 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 grid cell width located around the North Sea to simulate ambient air concentrations and depositions of B(a)P in September 2001. To evaluate the quality of the simulation results daily and monthly mean concentrations were compared to measurements from six monitoring stations. The ratio of modelled to measured values lied between a factor of 0.95 and 3.1 which – with respect to both measurement and simulation uncertainties and problems involved when comparing measurements with simulations – proved that our model is suitable to model fate and transport of B(a)P over Europe and can serve as a starting point for models for other PAHs considering also degradation.