Measuring and modelling the vertical distribution of semi-volatile organic compounds in soils. II: model development

A dynamic air-soil exchange model which divides the soil into multiple soil layers has been developed and used to simulate the vertical distribution of PCBs in an undisturbed grassland soil. An historical emission profile for PCBs to the UK atmosphere was used to deduce concentrations in the air compartment. Model simulations were tuned by varying the most uncertain model input parameters, namely soil turnover rates by bioturbation and emission estimates. Comparison of model output and reported PCB concentration profiles agreed within a factor of six. Insights were gained into the relative importance of the soil transport processes and specifically bioturbation was shown to be the dominant transport mechanism for PCBs in this soil. It was concluded that the model is sufficiently accurate for incorporation into regional mass balance models, although vertical layering of the soil may be unnecessary in models describing the long-term air-soil interaction of organic compounds.