Description and evaluation of a model of deposition velocities for routineestimates of air pollutant dry deposition over North America. Part I: model development

This paper describes the development of a detailed dry deposition model for routine computation of dry deposition velocities of SO2, O-3, HNO3 and fin e particle SO42- across much of North America, Four different dry depositio n/surface exchange sub-models have been combined with the current Canadian weather forecast model (Global Environmental Multiscale model) with a 3 h t ime resolution and a horizontal spatial resolution of 35 km, The present mo del uses the US Geological Survey North American Land Cover Characteristics data to obtain fourteen different land use and five seasonal categories. T he four sub-models used are a multi-layer model for gaseous species over ta ller canopy land-use types, a big-leaf model for gaseous species over lower canopies (including bare soil and water) and for HNO3 under all surface ty pes and, two different models for SO42-, one for tall canopies and the othe r for short canopies. All necessary parameters for each sub-model, chemical species, land-use and seasonal categories have been selected from availabl e data libraries or from the values reported in the literature, The purpose for developing this model (referred to as the Routine Deposition Model (RD M)), when coupled with air concentration data, is to provide estimates of s easonal dry deposition, which can be combined with wet deposition to produc e total deposition estimates. Model theory is discussed in this paper and m odel sensitivity tests and results will be presented in a companion paper. (C) 1999 Elsevier Science Ltd. All rights reserved.