Models regional acid deposition model

J. S. Chang and co-workers. The Regional Acid Deposition Model and Engineering Model, State-of-Science—Technology Report 4, National Acid Precipitation Assessment Program, Washington, D.C., 1989. 

McHenry, J. N., and R. L. Dennis, The Relative Importance of Oxidation Pathways and Clouds to Atmospheric Ambient Sulfate Production As Predicted by the Regional Acid Deposition Model, J. Appl. Meteorol., 33, 890-905 (1994). 

Stockwell, W. R., P. Middleton, J. S. Chang, and X. Tang, The Second Generation Regional Acid Deposition Model Chemical Mechanism for Regional Air Quality Modeling, / Geophys. Res., 95, 16343-16367 (1990). 

CIT = California Institute of Technology/Carnegie Institute of Technology UAM = Urban Airshed Model RADM 2 = Regional Acid Deposition Model. G-P = gas-particle. 

OZIPR contains two comprehensive chemical mechanisms that use two different approaches to lumping organics. The two mechanisms used in these models, the RADM (Regional Acid Deposition Model) and the Carbon Bond Mechanism (CBM), are discussed in Chapter 16.A.3b and in detail by Stockwell et al. [J. Geophys. Res., 95, 16343 (1990) and J. Geophys. Res., 102, 25847 (1997)] and by Gery et al. [J. Geophys. Res., 94, 12925 (1989)]. 

RADM2 The gas-phase chemical mechanism of Regional Acid Deposition Model, version 2... 

Stockwell WR, Middleton P, Chang JS (1990) The second-generation regional acid deposition model chemical mechanism for regional atmospheric chemistry modelling. J Geophys Res 95 16343-16367... 

Dennis, R. (1997). Using the regional acid deposition model to determine the nitrogen deposition airshed of the Chesapeake Bay watershed. In Atmospheric Deposition of Contaminants to the Great Lakes and Coastal Waters (Baker,. E., ed.). SETAC Press, Pensacola, FL. pp. 393—413. 

Regional Acid Deposition Models and Physical Processes. NCAR, Boulder, Colorado. 

These chapters provide examples of the types of approaches that are needed to better understand contaminant fate and transport. Some examples of aquatic models currently in use include the EPA-funded Green Bay and Lake Michigan Mass Balance Studies (36), and Chesapeake Bay Water Quality Model (37,38), Models have also been developed for atmospheric transport of pollutants including the Regional Lagrangian Model of Air Pollution (RELMAP)and the Regional Acid Deposition Model (RADM) (39,40)... 

A variety of models have been developed to study acid deposition. Sulfuric acid is formed relatively slowly in the atmosphere, so its concentrations are beUeved to be more uniform than o2one, especially in and around cities. Also, the impacts are viewed as more regional in nature. This allows an even coarser hori2ontal resolution, on the order of 80 to 100 km, to be used in acid deposition models. Atmospheric models of acid deposition have been used to determine where reductions in sulfur dioxide emissions would be most effective. Many of the ecosystems that are most sensitive to damage from acid deposition are located in the northeastern United States and southeastern Canada. Early acid deposition models helped to estabUsh that sulfuric acid and its precursors are transported over long distances, eg, from the Ohio River Valley to New England (86—88). Models have also been used to show that sulfuric acid deposition is nearly linear in response to changing levels of emissions of sulfur dioxide (89). 

Because of the expanded scale and need to describe additional physical and chemical processes, the development of acid deposition and regional oxidant models has lagged behind that of urban-scale photochemical models. An additional step up in scale and complexity, the development of analytical models of pollutant dynamics in the stratosphere is also behind that of ground-level oxidant models, in part because of the central role of heterogeneous chemistry in the stratospheric ozone depletion problem. In general, atmospheric Hquid-phase chemistry and especially heterogeneous chemistry are less well understood than gas-phase reactions such as those that dorninate the formation of ozone in urban areas. Development of three-dimensional models that treat both the dynamics and chemistry of the stratosphere in detail is an ongoing research problem. 

Atmospheric emissions of sulphur dioxide are either measured or estimated at their source and are thus calculated on a provincial or state basis for both Canada and the United States (Figure 2). While much research and debate continues, computer-based simulation models can use this emission information to provide reasonable estimates of how sulphur dioxide and sulphate (the final oxidized form of sulphur dioxide) are transported, transformed, and deposited via atmospheric air masses to selected regions. Such "source-receptor" models are of varying complexity but all are evaluated on their ability to reproduce the measured pattern of sulphate deposition over a network of acid rain monitoring stations across United States and Canada. In a joint effort of the U.S. Environmental Protection Agency and the Canadian Atmospheric Environment Service, eleven linear-chemistry atmospheric models of sulphur deposition were evaluated using data from 1980. It was found that on an annual basis, all but three models were able to simulate the observed deposition patterns within the uncertainty limits of the observations (22). 

The first step in the application of the concept was to determine the critical load values for the different regions of eastern Canada. This was done using historical measurements of lake acidity in concert with the Integrated Assessment Model (IAM) which links atmospheric transport and deposition models with water chemistry and empirical biological response models. Details of the method are given in Jeffries and Lam (1993). 

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