The uptake of hydrogen fluoride by a forest

A mathematical model of hydrogen fluoride (HF) deposition and accumulation of fluoride in a Eucalyptus rostrata forest has been developed. The model is based on tree physiology and meteorological principles. The data base for the model was derived from a literature survey of the physiological characteristics of E. rostrata and similar eucalyptus species and from current knowledge of meteorological processes in plant canopies.Comparison of the mathematical simulations with measurements in the vicinity of a source of HF (an aluminium reduction plant) shows that (1) the pattern of seasonal fluoride accumulation in leaves agrees with that seen in the field, and (2) the vertical pattern of accumulation inside tree leaves agrees with field observations. The simulations indicate that 50% of the released HF was deposited within 81 km of the source and that the concentration of HF in the air 81 km from the source was reduced to 2% of the concentration 1 km from the source. However, a very large forest area (20 600 km²) was required to achieve these reductions.