2.13 A Regional Multimedia Modelling System for the Simulation of the Long Range Transport, Chemistry and Deposition of Semi-Volatile Pollutants

摘要

We will report the development and application of a multimedia regional chemical transport model designed to investigate the long range transport and deposition of semi-volatile organic materials (SVOMs). The model was built by combining the US EPA MM5/MCIP/SMOKE/CMAQ modelling system with a dynamic air-soil exchange model, PEM (Pesticide Emission Model), which was developed by Canadian ORTECH Environmental Ltd. The combined model accounts for the important physical and chemical processes governing the behaviour of the SVOM in both the soil and the atmosphere. Hourly outputs from the modelling system include SVOM emission from the soil, its concentrations in both the gas phase and on atmospheric particulate matter and its wet and dry deposition to terrestrial and water surfaces. The CMAQ system used the CB4 mechanism and simulated common pollutants such as NO_X, VOCs and SO_2, which interacted with the SVOM. The model was tested by simulating the emission, transport, chemical reactions and deposition of toxaphene, a persistent, bio-accumulative, toxic pesticide. Although banned more than 20 years ago in North America, significant residues remain in the soil and these continue to be emitted slowly into the atmosphere. The model was evaluated from January 1 to December 31, 2000 in a domain that covers most of North America. Satisfactory agreement was obtained between the model predictions and measurements for: (a) daily-average toxaphene air concentrations, (b) fraction on atmospheric particulate matter, and (c) annual wet and dry deposition into Lake Ontario and the seasonal variations of these depositions.