INFLUENCE OF TEMPERATURE ON THE PLANT AIR PARTITIONING OF SEMIVOLATILE ORGANIC-COMPOUNDS/

Dry gaseous deposition is the main pathway of many SOCs to vegetation. It can be understood as a partitioning process between the plant and the gas phase. In this paper, the temperature dependence of the partit ioning of polychlorinated biphenyls between air and ryegrass (Lolium m ultiflorum) was investigated in the laboratory using a solid-phase fug acity meter, and the results were incorporated into a mathematical mod el of plant uptake of SOCs. The measured plant/air partition coefficie nts were exponentially proportional to the reciprocal temperature, in agreement with theoretical expectations. The enthalpy of phase change (plant/air) was linearly proportional to the enthalpy of vaporization of the subcooled liquid, but the agreement between the two parameters was poor, the enthalpy of phase change (plant/air) being lower than th e enthalpy of vaporization for the lower chlorinated PCBs and much hig her for the higher chlorinated PCBs. The model simulations showed that under environmental conditions the temperature dependence of the part itioning coefficient does not influence the plant concentrations of mo st SOCs. The slow uptake/clearance kinetics prevent the plant/air syst em from reacting quickly to the new equilibrium state resulting from t he temperature-induced change in the partition coefficient. Only for m ore volatile compounds such as trichlorobiphenyls or phenanthrene can the plant/air concentration ratio be expected to react to changes in t emperature.