Regional and intercontinental modelling - Air Pollution Modeling and Its Application - page 158

2.13 A Regional Multimedia Modelling System for the
Simulation of the Long Range Transport, Chemistry

and Deposition of Semi-Volatile Pollutants

Rong Li 1 , M. Trevor Scholtz 2 , Fuquan Yang 1 , and James J. Sloan 1

1

Waterloo Centre for Atmospheric Sciences, University of Waterloo, Waterloo, ON, Canada

2

Canadian ORTECH Environmental, Mississauga, ON, Canada

Abstract 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 model-
ling 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 pre-
dictions 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.

Keywords Multimedia, chemical transport model, semi-volatile pollutant, pesticide

1. Introduction

Toxaphene, a mixture of chlorinated bornanes, is an effective pesticide for cotton,
soybean and corn. Beginning in the 1940s, it was used heavily in the United States