Monitoring pops in a complex environment: the role of modelling

Pollutants released by large industries are often a cause of major concern for local communities living nearby. Traditional monitoring consists of continuous emissions controlling systems (CEMS) and regular sampling of flue gas associated with monitoring stations positioned at best for checking on air quality where people reside. Sometimes a remote monitoring station is employed to set a background pollution reference value. In the case of Persistent Organic Pollutants (POPs) this may not be the best planning strategy for monitoring exposure. In fact, direct exposure through inhalation forms just a minor contribution to the total people exposure. A much more relevant exposure is indirect, due to the ingestion of food, either vegetable or animal, which has been contaminated. For this reason, a great care should be put in placing monitoring instruments where deposition of POPs is larger, especially when industrial and rural areas are bordering. As an example, we present the case of a steel foundry in an alpine valley, emitting PCDD/Fs and PCBs besides traditional air pollutants. Using all the available data registered by the CEMS installed on the main chimney, hourly concentration and deposition fields have been obtained by running a one year long simulation with the three dimensional lagrangian model SPRAY, capable of simulating both dry and wet deposition. Due to the complexity of the local topography, a 250m horizontal spatial resolution grid has been used. Meteorological fields have been obtained at the same resolution by a downscaling procedure with a mass-consistent model (SWIFT). The statistical analysis of the results shows the relevance of secondary fallout patterns in remote areas, where vegetables could be grown for local consumption or dairy cattle could frequently pasture, thus suggesting the need of specific monitoring for remote areas in order to attain a wider assessment of human exposure.