International Air Quality Advisory Board
SPECIAL REPORT ON
November 1998
4. MONITORING and MODELING As noted in the Introduction, the goal of this report is to review current transboundary air issues using a "one atmosphere" or "seamless border" approach. Because the atmosphere knows no borders and plays a major role in the transport and transformation of pollutants that can affect public health and ecosystems across North America, it is only logical that the United States and Canada attempt to address air pollution issues in this context. The seamless border approach is particularly relevant to the various tools used to examine and understand air issues and policies. Two of these tools are monitoring and modeling. There have been several bilateral monitoring projects between the United States and Canada, the most notable being the field of acid deposition. From 1981 to 1983, an intercomparison study of Canadian and U.S. wet deposition measurements was carried out by collocating precipitation chemistry samplers at several Canadian and U.S. sites. The results, published by Bigelow (Environmental Science & Technology, 1991), clearly pointed out that Canadian measurements were deficient. This led directly to the formation of a new, improved Canadian wet deposition network, the Canadian Air and Precipitation Monitoring Network (CAPMoN). The valuable information gained from the first intercomparison study and the recognition of the need to ensure the compatibility of the two countries' data led both countries to collocate wet deposition instruments at one site in each country (at Pennsylvania State University in Pennsylvania and at Sutton in Quebec). A second study (the results of which are about to be published) demonstrated that both countries' sulfate measurements are highly comparable, although measurement of other species (such as ammonium and hydronium) is not. The information from this study played a part in the NADP/NTN network's decision to change monitoring protocols in 1994. At present, the collocation study has been expanded to further identify why differences between the two countries exist, with a goal of eventually harmonizing the measurements. The study has now collocated the samples of four different networks at the Penn State intercomparison site: CAPMoN, NADP/NTN, AIRMoN, and CASTNet. The results will be described in a multi-agency paper currently under preparation. These intercomparison studies have helped define the uncertainty associated with North American wet deposition maps created by merging U.S. and Canadian wet deposition data. A similar process has been undertaken in the field of air quality measurements. Of particular note was a comparability study carried out during the U.S.Canada Eulerian Model Evaluation Field Study (EMEFS), in which two Canadian and two U.S. filter pack sampling networks were intercompared at Penn State. The results, which were published by McNaughton and Vet (Atmospheric Environment, 30:2, 1996), showed that the uncertainty of the measurements by the two countries was within 10 per cent for all species measured. The study subsequently led to a long-term U.S.-Canadian intercomparison study of air concentration measurements and dry deposition estimates. The latter study is taking place at the Centre for Atmospheric Research Experiments in Egbert, Ontario, where both CAPMoN and CASTNet filter pack/dry deposition sampling instruments are collocated. The study results, described in preliminary form in the 1994 CanadaUS Air Quality Agreement Progress Report, indicate a high level of comparability for sulfate and nitrate measurements, but poorer comparability for SO2 measurements. A statistical comparison of U.S. and Canadian dry deposition estimates at this site will soon be undertaken to determine the compatibility of the inferential dry deposition models and estimates from the two countries. The close collaboration between U.S. and Canadian scientists in the measurement (and model development) areas is leading to closer harmonization of both. Another example of comparison studies is the Integrated Atmospheric Deposition Network (IADN), a joint U.S.Canadian monitoring network that addresses PTSs transported to and deposited in remote areas of the Great Lakes. The IADN is made up of five master stations and several satellite stations on both sides of the Great Lakes. It has provided the necessary standardized methods, monitoring data, and loading estimates to allow first assessments of the relative importance of atmospheric deposition compared with other inputs (e.g. effluents and sediments) within the Great Lakes. The IADN does not specify samples or sampling protocols, as long as comparability among all participants can be established. At each site, concentrations of target chemicals are measured in rain and snow (wet deposition), airborne particles (dry deposition), and airborne organic vapors. Precipitation rate, temperature, relative humidity, wind speed and direction, and solar radiation are also measured. The Quality Control-Quality Assurance program developed as part of the IADN has been used as a model in other efforts to measure toxics in the atmosphere, such as the St. Lawrence Action Plan, the Lake Michigan Mass Balance, and the European Monitoring of the Environment Program (EMEP). Similar examples of collaborative modeling can be cited. For example, as part of the efforts to address the acid rain issue, an External Review Panel of the EMEFS used data from an extensive field study undertaken during 1988 and 1990 to review two Eulerian models: the U.S. Regional Acid Deposition Model (RADM) and the Canadian Acid Deposition Oxidants Model (ADOM). That review, which was described in a report published in May 1994 (Report of the Fourth Meeting of the External Review Panel, Niagara-on-the-Lake, Ontario Canada), drew the following conclusions:
Since that comparison, work to improve the models and their associated chemistry modules has continued. A more recent example of a collaborative modeling effort is the binational North American Research Strategy on Tropospheric Ozone (NARSTO). Presently, a proposal is being put before NARSTO's Executive Committee to intercompare Canadian and U.S. models using field data collected as part of the two recent NARSTO field campaigns. The intent is to work jointly on developing the best modeling techniques to address the North American ozone issue. The preceding discussion demonstrates the successes to date stemming from the cooperative work of the United States and Canada in the development of both monitoring and modeling to address air issues that recognize no borders. Four current issues remain, however, where such collaborative efforts should be enhanced. First, in the monitoring area, the U.S. EPA is presently proposing to install 1,500 monitoring sites nationwide for fine particulate ( PM2.5). Simultaneously, Canada is enhancing monitoring networks to address the fine particulate issue. There is some question, however, as to whether the instrumentation being installed in the two networks will yield comparable data. Second, in the modeling area, the U.S. EPA is developing a Models-3 project. The project is intended to develop a flexible and general modeling system/platform to support multi-pollutant and multi-scale air quality simulation, while taking advantage of the enhanced computational capabilities provided by high-performance computing and communications systems. The Models-3 project will allow different chemical and meteorological modules to be run simultaneously. The Board believes it is important to ensure that Canadian scientists and modelers are involved in the Models-3 project throughout its development and use. Third, collaboration between the two countries will be important in conducting additional mass balance studies in waters along the border. The contribution of the various sources of environmental pollutants, particularly PTSs, needs to be better understood in the border regions and beyond. Much has been learned from the application of mass balance models in the Great Lakes and the Gulf of Maine. This type of analysis should now be completed to better understand air pollution impacts in the Pacific, ArcticFar North and Lake ChamplainSt. Lawrence regions. Finally, the current IADN consists of five regional background measurement stations, one on each of the Great Lakes. Because these five sites avoid urban regions and industrial plumes, the net result is good regional estimates of concentrations of several organic and inorganic contaminants. This approach is flawed, however, in that it does not consider that many of the larger particles are generated and concentrate in more developed areas. Estimates of deposition of some materials to the Great Lakes are thus likely to be low by an undetermined amount. A more complete understanding of the relative importance of atmospheric deposition of pollutants will require deposition measurements in and around urban areas. Recommendations Based on the its review of monitoring and modeling activities for both common pollutants and PTSs, the Board recommends the following:
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