PROGRESS REPORT 2000 

Long-Range Transport Challenge Update

Under the Great Lakes Binational Toxics Strategy, EC and EPA committed to

"Assess atmospheric inputs of Strategy substances to the Great Lakes. The aim of this effort is to evaluate and report jointly on the contribution and significance of long-range transport of Strategy substances from worldwide sources. If ongoing long-range sources are confirmed, work within international frameworks to reduce releases of such substances."

In support of this challenge, the US and Canada have:

• Maintained the Great Lakes Integrated Atmospheric Deposition Monitoring Network
• (IADN) stations,
• Improved the integration of monitoring networks and data management, and
• Continued research on the atmospheric science of toxic pollutant transport.

Following the strategy's 4-step analytical framework to evaluate and report jointly on the contribution and significance of long-range transport of Strategy substances from worldwide sources, the EC and EPA have accomplished the following:

Step 1. Information Gathering

ACTION:

A literature review and assessment of the long-range transport of persistent toxic substances to the Great Lakes was undertaken in 1999, and a report was published by the Canadian firm ORTECH Environmental on March 27, 2000. The following is the Executive Summary of that report, entitled Long-range Transport of Persistent Toxic Substances to the Great Lakes: Review and Assessment of Recent Literature.

In 1997, Canada and the U.S. signed The Great Lakes Binational Toxics Strategy (GLBTS) which has the virtual elimination of persistent toxic and bioaccumulative substances from the Great Lakes ecosystem as its aim. Two classes of substances, designated Level I and II, are being addressed by the GLBTS as well as by the Binational Virtual Elimination Strategy (BVES) for persistent toxic substances. The Level I substances are given higher priority for elimination than the Level II class of substances. One target of these initiatives is the identification of atmospheric inputs of toxic substances to the Great Lakes due to worldwide sources; the present study, commissioned by the Atmospheric Environment Service of Environment Canada, contributes to this initiative. The overall study objective is the review the feasibility of making estimates of the fraction of each Strategy substance that is likely arriving to each of the Great Lakes via the atmosphere from local, continental and global sources, and where feasible, make such estimates. Modeling or deposition estimate calculations were not within the scope of the study.

A prior compilation of literature up to 1997 on deposition to the Great Lakes, commissioned by the International Joint Commission's International Air Quality Advisory Board, was the starting point for the present study, and only literature that has appeared since 1997 was presently reviewed. Scientists at Environment Canada had a consultative role in this study to provide expertise and guidance in the overall approach to the work. In addition, direct contact was made with other researchers to obtain information on work that is still in progress.

As a first approach, information on the atmospheric life-times of GLBTS substances was reviewed to assess their likely transport distances in the atmosphere. On the basis of these estimates, sources of toxics in regions beyond their likely transport ranges, can be disregarded in assessments of Great Lakes impacts. The two main mechanisms that remove airborne toxics from the atmosphere and limit their atmospheric life-times are: (1) chemical and photochemical destruction; and (2) wet and dry deposition that deposit the substances on land and water surfaces. A preliminary attempt has been made in this report to identify the dominant source distances contributing to the deposition of GLBTS substances to the Great Lakes. The distance estimates are based on published atmospheric life-time estimates and on inferences gleaned from studies presently reviewed. A review of emission sources and their global distributions is provided in the report. By combining the atmospheric life-time with a knowledge of the distribution of sources and at the local, regional, intercontinental, and global scales, first order estimates can be made of the potential contribution of long-range transport to Great Lakes deposition.

Sources of BVES substances were reviewed at local, regional, intercontinental, and global scales and were found to be extremely varied. Substances that are formed during combustion process, for example, have almost a global distribution, while other substances are banned from use in some regions of the globe but continue to have use in other areas. Although sources of BVES substances appear to be fairly well known, there is a need to further develop high quality emission inventories that address both point and area sources at the spatial resolution required by models. Of the 28 BVES substances that have a long range transport, five have potentially sufficient global inventory data to support modeling efforts. For banned substances there is a need to address past use to account to residues in soil, especially at the local and regional scales. By combining information on atmospheric life-times and distribution of sources and at the local, regional, intercontinental, and global scales, first order estimates can be made of the potential for long-range transport contributions to Great Lakes deposition.

The second approach to quantifying the contribution of long-range transport to Great Lakes deposition involves the application of transport models. Both Lagrangian trajectory and Eulerian transport and deposition models have been used to study Great Lakes impacts. Lagrangian models can be used for deriving source-receptor relationships over regional or smaller scales, however, they are limited in their application for global transport and deposition studies due to inherent limitations for simulating the complex 3-D global transport processes that are driven by global meteorology. It is concluded that comprehensive Eulerian models are potentially superior tools for providing quantitative estimates of the relative contributions of the different source regions of the globe to Great Lakes impacts.

While several modeling studies are found in the literature, few of the studies reviewed quantify the relative contributions of global source regions to Great Lakes deposition. The overall conclusion of this review is that while several qualitative assessments and quantitative modeling studies are reported, there is very limited information available to quantitatively link emission sources at global, continental, regional or local distance to Great Lakes impacts.

Both Lagrangian trajectory and Eulerian transport and deposition models have been used to study Great Lakes impacts. In cases where the grasshopper effect does not play a significant role, and where chemistry and partitioning between phases in the atmosphere are relatively simple, Lagrangian models can be used for deriving source-receptor relationships over regional or smaller scales. Lagrangian trajectory models are, however, limited in their application for global transport and deposition studies due to inherent limitations for simulating the complex 3-D global transport processes that are driven by global meteorology. It is concluded that comprehensive Eulerian models are potentially superior tools for providing quantitative estimates of the relative contributions of the different source regions of the globe to Great Lakes impacts. Further model development is needed, however, particularly in modeling the micro-kinetics involving wet and dry atmospheric particulates and aerosols, and in the air-surface exchange with terrestrial surfaces.

For other substances, a preliminary attempt has been made in this report to identify the dominant source distances contributing to the deposition of BVES to the Great Lakes. The distance estimates are based on published atmospheric life-time estimates and on inferences gleaned from studies presently reviewed. I is emphasized that these results are subjective, and at best, they are very low order estimates that might be used with caution to provide some guidance for future studies. While several modeling studies are found in the literature, few of the studies reviewed quantify the relative contributions of global source regions to Great Lakes deposition. A recent Lagrangian model study, however, does address the deposition of polychlorinated-p-dioxins to the Great lakes from sources in the U.S and Canada. This study shows that for Lakes Superior and Huron, between 20 and 40% of the deposition in 1995/1996 was due to sources at regional distances (400-1500 km) from the lakes while for the other three Lakes, local sources (within 100 km) contributed between 40 and 60% of the total dioxin deposition; depositions contributions by sources in other parts of the globe would reduce these percentage estimates.

The overall conclusion of this review is that while several qualitative assessments and quantitative modeling studies are reported for atmospheric transport and deposition to the Great Lakes, there is very limited information available to quantitatively link emission sources at global, continental, regional for local distance to Great Lakes impacts.

The following recommendations arise from this study:

• For comprehensive models, a better understanding of the roles of particulates, aerosols and terrestrial surfaces in heterogeneous chemical and photochemical reactions of BVES substances should be developed and the models should be extended to include the microkinetic processes for toxics involving atmospheric particulates and aerosols as well as the exchange of toxics with terrestrial surfaces;
• Effort should be directed toward the complilation of high quality emissions inventories for BVES substances on appropriate scales for model input; fir banned pesticides that are still used in other parts of the globe, and have significant soil residues in North America due to historical applications, effort should be directed toward measuring surveys to define the distribution of these residues on appropriate scales for modeling;
• To reduce the large effort required to address all BVES substances, a sub-set of substances should be selected for study that are representative of the different ranges of physical-chemical properties.

Step 2. Analysis

ACTION:

A binational workshop for early 2001 is in the planning stages.

Next Steps

In the spring of 2001, EC and EPA will hold a workshop that will bring experts together to help characterize data gaps, solicit pertinent information, and recommend options for a path forward. Once data gaps have been identified, information will be solicited to help quantify substance characteristics, gather usage/emission inventory information within and outside the basin, collect ambient measurement information, and evaluate previous models or assessments of atmospheric transport.