This is a preliminary document prepared by a subgroup of members of the National and Regional Strategies Work Group as part of the Federal Advisory Committee Act (FACA) Subcommittee process. It is not an EPA document. It is subject to further work group discussion. Interested people should forward their comments to a member of the National and Regional Strategies Work Group.

ISSUE TITLE: How should areas of influence be determined?

CONTACT: Don Theiler, Wisconsin representing NRS work group @ (608)266-0603

DATE: September 19, 1996

BACKGROUND

The "area of influence" (AOI) is a specified domain containing the set of anthropogenic and non-anthropogenic sources potentially contributing to downwind "areas of violation" (AOVs). All areas within an AOI will be required to participate in the development of a spatially integrated air quality management plan. An AOI designation does not mean, however, that all portions of the area will be required to implement regulations, nor does it indicate that sources in all portions of the area will be subject to regulations. The spatially integrated air quality management plans will address details, such as which portions of the AOI should be subject to regulation and what the regulations should be. These complexities should be avoided as much as possible in the initial AOI determinations. In addition, new source issues will be dealt with in subsequent discussions.

Readers are encouraged to refer to the July 25, 1996 version of the Designations for New NAAQS joint issue paper for NRS work group recommendations and more in-depth discussion concerning AOIs and AOVs. Building on the ideas introduced in the Designations paper, this paper presents a range of options for determining AOIs. In the Designations paper, it is assumed that being included in an AOI will result in all portions of the area being required to be a part of a spatially integrated plan. It does not mean that all portions of the area will be required to implement regulations or have sources in all portions of the area be subject to regulations. With this in mind the operating principle in defining the AOI becomes that of including all areas or sources which might conceivably contribute to the violation. Freelance Graphics file called AOIPAPR3.PRE on the Technology Transfer Network (TTN) Bulletin Board System provides illustrations of the following options. The options are conceptual approaches; details will be developed at a later date.

This paper presents a three step approach for implementation. The first step is the development of a large planning region. All 48 contiguous States will participate in these planning regions. Identification of AOI's is the second step and will be done by the large planning region. The planning region will also deal with overlapping AOI's. The AOI will develop a spatially integrated air quality management plan. This plan will result in the identification of control and trading regions. Identification of control and trading regions is the third step.

PROBLEM STATEMENT

As first discussed in the Designations for New NAAQS issue paper, there are numerous problems with the current nonattainment area designation process. In summary, a designated nonattainment area is generally defined using political boundaries and air quality data. Controls are then required within the nonattainment area. This results in a bright line around the nonattainment area which may cause sources to locate outside the nonattainment area to avoid control requirements. In addition, states may be reluctant to monitor air quality as it could result in a nonattainment designation that will trigger planning and reporting requirements for the state. Finally, the current system does not address transport of pollutants into the nonattainment area. Many of these issues could be mitigated using the AOI/AOV construct.

This paper focuses on options to define the AOI (not the AOV). The first six options (A through F) focus on the mechanics of defining the AOI. The last four options (G through J) is more oriented toward defining the size of the AOI.

Potential issues have been identified regarding the definition of AOIs. First, determining source attribution for ozone, PM-fine, and regional haze is complex, requiring sophisticated atmospheric chemistry models, detailed meteorology, and supporting speciated air quality monitoring data. The availability of a full set of tools and data within the integrated implementation time frame is unlikely. Second, keeping planning areas a reasonable size will result in many regions, which places a demand on the State organizations participating in the development of the spatially integrated air quality management plan, industry, and advocacy groups. Third, current scientific evidence demonstrates a difference between the east and the west (with a split at roughly the 100th meridian). Treating the east and west as two super planning regions will split some states (most notably Texas). Finally, seemingly arbitrary decisions (what is X) may be required for some of these options.

This paper does not address the size or determination of control regions or potential trading zones.

OPTIONS

Option A1. The AOI and AOV are equivalent and directly overlap. This option is the current approach for designating nonattainment areas. It requires relatively inexpensive tools and is readily defined. Disadvantages include an inadequate treatment of air pollution transport.

Option A2. The AOI is defined as the source of activity exterior to the AOV. The AOI and AOV could be separate or somewhat overlapping. An example of this option would be a Class I area impacted by a single source or source category. This approach relies on a readily defined area of emissions and its applicability may be limited to addressing primary PM and PM10 problems. Another disadvantage is the resources required to demonstrate the causal effect of the single source or source category.

Option B. The AOI is defined by X miles out from the AOV or using a definable statistical routine on the source impact. Advantage are that both methods are easily described. Disadvantages with both methods are that they will result in numerous overlapping areas and they both rely on an arbitrarily defined X or defined statistical parameter. Neither approach accounts for terrain.

Option B1. Whether X is measured from the AOV's center or the perimeter would need to be determined. This option could be difficult if the AOV is not a circle, otherwise it requires minimal labor. In addition, this approach may be illegal in the regional haze program, because buffer zones may not be delineated.

Option B2. This option would use a predefined statistical parameter of the source/impact characteristics of the individual AOI. Therefore each AOI boundary would be more closely associated with the source/impact characterization of that individual AOI. The selection of the predefined statistical parameter becomes arbitrary. This option would not consider small sources outside the AOI that impact the AOV.

Option C. The AOI is defined by emission density maps. This option is similar to B2, except emission density maps are used instead of a statistical technique. The AOI boundaries are based on clustering of sources and knowledge of emission densities and activities. The AOI could be defined as counties with emission densities greater than X tons per square mile. Determination of X may seem arbitrary. Unless emission density by a uniform grid is used, physically large counties have an advantage. This simple and intuitive option is easily translated into emission control strategies. This approach, however, does not account for atmospheric chemistry effects, and it may be detrimental for small source credit production. Another drawback is the possibility of a low emission density around the AOV with a high density some distance away from the AOV. Finally, this approach may become arbitrary.

Option D. The AOI is defined by sources X days away from the AOV where the sources are determined using a back-trajectory analysis. Determination of X may be arbitrary. The technique to define X days has not been determined. While this approach is intuitively appealing, it may be difficult to translate into a geographic area. In addition, there will be numerous sources participating in more than one AOI.

Option E. The AOI is defined by a cap of X% of the modeled impact. The AOI would extend outward from the AOV until X% of the modeled impacts have been accounted for. This intuitively appealing approach is similar to C, except modeled impacts are used instead of emission densities. Disadvantages of this option are the possibility of numerous overlapping AOIs and the difficulty of choosing (and the availability of) appropriate models and meteorological periods. It may discourage contributing sources located outside the area from participating in the planning process. Finally, it could require source-specific modeling analyses.

Option F. The AOI is defined as "greater than X%" of the modeled impact. Either a grid-by-grid or source-by-source modeling exercise could be used. Because this approach captures all sources with a greater than X% impact on the receptor, discontinuous AOI boundaries are conceivable. The AOI could consist of a contiguous region encompassing options B, C, D, or E plus discontinuous areas outside. This option has the advantage of bringing in sources from far-out distances. It also captures the major players and ensures that reductions occur where they will improve the problem. The disadvantages are the same as those listed under option E. It also does not account for smaller sources contributing to the problem.

Option G. This option introduces the concept of identifying, for each event, the area from which source activity was responsible for the exceedance during that event. The results are then summed into a larger AOI covering all potential events. Each individual study could use any of the options above. For the purpose of this discussion, Options D & E would be the most probable method for identifying the source contribution. The amoeba shape is created by combining the areas of influences from intersecting areas created by the exceedances. This approach allows all possible participants in the exceedance of air quality standards for one area of violation to trade. However, the amoeba shape for one area of violation may intersect with another similarly drawn area for a different area of violation resulting in sources participating in more than one area of influence. Drawbacks are the necessity of complex modeling exercises and the possibility of wrong way trades.

Option H. The AOI is defined as the State boundary in a multi-State amoeba situation. This option applies political borders to the analysis results from option G. This approach eliminates the disincentive for sources to locate just outside the boundary of the AOI. This option, however, could result in States participating in numerous AOIs. Presumably the AOIs do not overlap (or they would become one AOI) but one state may have pieces of more than one AOI. It also may prohibit some advantageous trades across jurisdictions.

Option I. The AOI is the entire country or eastern and western regions. Eastern and western regions could be created with the dividing line at approximately the 100th Meridian as this is the physical boundary where evaporation is more dominant than precipitation and the chemistry and transport patterns are very different on either side of this approximate dividing line. The regional data for ozone and the Class I monitoring program for visibility clearly support this division. This would establish two large zones for coordination on planning and data development (emission inventories, air quality monitoring, and air quality model development).

The large AOIs address previous concerns with overlapping AOIs. This option provides the largest area for emission trade, includes many possible participants, and addresses transport and concerns for locating new sources on the other side of a bright line. One drawback is the potential for "unwieldy management" and this option may not address the varying levels of control needed within the super large AOI. This option may allow wrong way trades where the reductions achieved may not affect where the increases occur.

Option J. The AOI would be determined with a combination of option I and a process for designating subregions. At least two large planning regions (e.g., eastern and western) are created. States within each planning region determine smaller subregions, which could be the control regions within the AOIs. The smaller subregions allow more focused strategies to be developed for the NAAQS and reasonable progress for visibility in the Class I areas.

The approach ensures everyone participates in the planning process. It allows control measures to be applied wherever they are appropriate. In addition, it may avoid wrong way trades. The methodology for defining the subregions must be determined and may be considered arbitrary. Some States may be part of more than one subregion. Wrong-way trades may still occur.

RECOMMENDATION

The National and Regional Strategies - Control Regions subgroup, had a face-to-face meeting on September 4, 1996 to discuss these options. Initially the group expressed support for identifying individual AOI's using back trajectories or X% of the modeled impact for all exceedance events for that AOV. When faced with the very real potential for many of the individual AOIs overlapping with other AOI's it was also recognized that a larger planning area would need to be identified to deal with the identification of the larger integrated AOI's. There larger integrated AOI's would include multiple AOV's within an area. It was concluded that identifying the large integrated AOI's should be undertaken by a large group of states such as those identified under the regional and/or subregional options (I and J).

On September 5, 1996 the National and Regional Strategies work group reached consensus on the following recommendations:

I.	The identification of AOIs should be undertaken by states participating in broad subnational planning regions (as suggested in Option J). The broad subnational planning regions should be formed by dividing the U.S. into, at a minimum, eastern and western planning regions. All 48 contiguous states would be included in a planning region. The ultimate number of planning regions and the specific boundary for the regions will be determined following approval of the general approach.

II.	The planning regions would determine the specific AOIs and would address the mechanism for identifying broad integrated AOIs following the specifications of AOVs and the Class I areas. The integrated AOIs would take account of overlapping individual AOIs for the same pollutant as well as for separate pollutants and regional haze. It is anticipated that there will be considerable overlap of individual AOIs and that integrated AOIs will be needed in some areas of the nation (e.g. ozone in eastern region and regional haze in western region). The method for determining the AOIs will be back trajectories and/or percentage of modeled impact. The specific technique used would be determined by the states participating in the planning regions at that time.

III.	If an AOI includes all or any part of a state, that state will be required to participate in the development of a spatially integrated planning process for that AOI. The spatially integrated plan will identify the specific strategy which will be employed to bring the AOV or AOVs within that AOI into attainment with the standard. It will also address the regional haze needs of that AOI.

IV.	Localized AOVs are identified as those AOVs where the AOI would not extend across the boundary of the state in which the violation is occurring. Localized AOVs can be identified by the state in which the violation is occurring or by the Environmental Protection Agency. If a localized AOV is identified that area would not be required to participate in any interstate planning efforts and the affected state would be responsible for developing a separate attainment plan for that area.

ADVANTAGES & DISADVANTAGES OPTIONS PROS A1 A2 B1 B2 C D E F G H I J Requires inexpensive tools and minimal labor (no modeling) X X X X Easily defined area X X X X X X X Easily explained X X X X X X X X X Easily translated into emission control strategies X X X X X X Brings sources from significant distances into planning X X X X X X X Ensures improvements occur where health risks are located X X X X X X X X Allows everyone to participate in the planning X X X X X Eliminates incentive for sources to locate just outside boundary (bright line) X X X X Addresses transport issues X X X X X X X Allows most number of trades, many participants, solves transportation location issues X X CONS Does not address transport issues X X X X X Limited applicability X X X Allows directionally wrong trades* X X X X X X X Results in numerous overlapping AOIs X X X X X X X X X X X Involves arbitrary decisions X X X X X X X X X X X X Misses small sources X X X X X X X X X X X Does not account for terrain X X X X Does not account for atmospheric chemistry (no modeling or transport) X X X Illegal for regional haze program which does not allow buffer zones X Discourages participation from sources outside AOI X X X X X X X X Difficult to translate into geographic area X X X Prohibits advantageous trades across jurisdictions X X X Requires complex modeling, including source-specific modeling X X X X X X X X

* With decreasing probability as you move from option D through J.