Wyoming Department of Environmental Quality

Modeling Studies

Southwest Wyoming NO₂ PSD Increment Consumption Analysis and Modeling

The Wyoming Department of Environmental Quality - Air Quality Division (WDEQ-AQD) has completed an extensive analysis and modeling study designed to obtain the best possible estimate of the cumulative nitrogen dioxide (NO₂) prevention of significant deterioration (PSD) increment consumption from sources impacting southwestern Wyoming. The focus of the analysis are the Bridger and Fitzpatrick Wilderness Areas (which are Federally designated Class I areas), along with the surrounding Class II areas.

This study consists of four tasks:

Task 1 was designed to provide WDEQ-AQD with a quick, initial estimate of NO₂ impacts at current emission levels from sources of NO_x emissions in Sublette County based on the most readily available nitrogen oxides (NO_x) emissions data (2002).

The Task 2 modeling analyses were designed to refine and extend the Task 1 analysis by A) using the new 2004 Sublette County NO_x emission inventory, B) determining, via a series of detailed sensitivity analyses, the most appropriate modeling configuration, and C) modeling NO₂ increment consumption associated with NO_x sources in Sublette County as of 2004, as well as the Bridger and Naughton power plants in southwestern Wyoming.

Tasks 3 and 4 were conducted in 2006 to further refine the NO₂ PSD increment consumption modeling analysis by including emissions from all significant sources of NO_x within a 300 kilometer radius of the Bridger and Fitzpatrick Wilderness Areas, and extending the results to include simulations based on three (3) additional years of meteorological data.

Results of Task 1 and Task 2 Modeling Analyses

●    Task 1 Technical Memorandum
●    Task 2 Summary Report
●    Task 2 Final Report

Results of Task 3 and Task 4 Modeling Analyses

●    Final Report - Southwest Wyoming NO2 PSD Increment Consumption Analysis

●    Appendix A - Sample CALMET Control Parameters Input File
●    Appendix B - CALMET Wind Vector Plots for Top 10 NO2 Concentration Days
●    Appendix C - Monthly Mean CALMET Wind Vector Plots
●    Appendix D - Seasonal Mean CALMET Mixing Heights
●    Appendix E - Example CALPUFF Control Parameter Input File

Modeling Protocol

● Southwest Wyoming NO2 PSD Cumulative Increment Consumption Modeling Protocol

Presentations on Southwest Wyoming NO2 PSD Increment Study

● Presentation on Work Completed Through June 2006
● Presentation on Work Completed Through August 2007

Southwest Wyoming Technical Air Forum

Prevailing winds transport emissions from the southwest quadrant of Wyoming into the Bridger and Fitzpatrick Class I Wilderness Areas. The southwest quadrant of Wyoming is relatively highly industrialized with a group of five large trona plants, several sweet and sour gas plants, two coal-fired power plants, a large number of internal combustion compressor engines associated with gas production and transportation activities, and the oil and gas production equipment at each well. Due to concerns about the assessment of industrial development impacts on southwest Wyoming air quality, visibility, and other air quality related values (AQRVs) the Southwest Wyoming Technical Air Forum (SWWYTAF) was established in 1996. The Forum is comprised of representatives from the Wyoming Department of Environmental Quality, United States Forest Service, Region VIII of the Environmental Protection Agency, Wyoming State Office of the Bureau of Land Management, Shoshone and Arapaho Tribes, industry, and environmental organizations.

In 1997 the SWWYTAF authorized the Southwest Wyoming Regional Haze Modeling Study for the purpose of estimating air impacts on the Bridger and Fitzpatrick Class I Wilderness Areas and evaluating the performance of the CALPUFF/CALMET dispersion modeling system. Due to the consideration of pollutants being transported into the southwest quadrant of Wyoming by prevailing winds, additional sources of emissions from southeastern Idaho, northeastern Utah and northwestern Colorado were considered in the establishment of the study region. The following is a map of the modeling domain.

Emissions of pollutants of concern include nitrogen oxides, primary particulate matter, sulfur dioxide, volatile organic compounds, and ammonia. The major purpose of the study is to evaluate the degree of degradation to air quality, visibility, and other AQRVs in these Class I areas that is caused by upwind anthropogenic and biogenic sources. A second purpose is to evaluate the performance of the spatially and temporally non-uniform CALPUFF Gaussian dispersion model and its related wind field module CALMET in comparison with 1995 measured air quality and AQRVs in the Class I areas.

The complexity of the work required to develop a detailed emissions inventory for air quality modeling as well as unexpected delays in the application of the modeling system have resulted in the significant timeline delays for the SWWYTAF modeling study. The modeling study was completed during the summer of 2001. Reports documenting the emissions inventory and modeling study are described at the end of this section and are available upon request.

The modeling study has been jointly funded by industry, Federal Land Managers, Federal grants, and the Wyoming Department of Environmental Quality.

The SWWYTAF modeling study resulted in an executable model that is available upon request to Wyoming Federal Land Managers, Tribes and industry for their use to determine impacts to visibility and air quality in the Bridger and Fitzpatrick Class I Wilderness Areas. The Air Quality Division proposes to track the impact of minor source growth on the Bridger and Fitzpatrick Class I Wilderness Areas and intends to perform a Prevention of Significant Deterioration (PSD) Class I NO2 increment consumption analysis using components of the SWWYTAF modeling system, which will then be used for future NO2 increment tracking. The Air Quality Division has and will use components of the SWWYTAF modeling system in analyzing impacts from major PSD source applications. The Division is also planning to update the emissions inventory to 2002 actual emissions and utilize components of the SWWYTAF modeling system in developing strategies that will be implemented in Wyoming’s Regional Haze State Implementation Plan.

To resolve concerns expressed by SWWYTAF participants regarding the SWWYTAF Final Report, the SWWYTAF Technical Committee prepared a SWWYTAF Technical Committee Summary to accompany the SWWYTAF Final Reports and Project Files. The SWWYTAF Technical Committee Summary identifies, among other things, the uses for which the model is valid or not valid as well as concerns and drawbacks for the application of the model.

SWWYTAF Technical Committee Summary

Volume I The Southwest Wyoming Regional CALPUFF Air Quality Modeling Study - Final Report
(Summarization of 1) the emissions inventory used in the modeling effort, 2) the geophysical, meteorological, and air quality databases used in the modeling effort, 3) the modeling approach used in the modeling effort, 4) the results of the model evaluation study, and 5) a summary of the major findings and conclusions of the study.)

Volume II The Southwest Wyoming Regional CALPUFF Air Quality Modeling Study - Final Report
(Contains the appendices to Volume I. The appendices contain more detailed information regarding the modeling inputs, predicted concentration and deposition fluxes in the Class I areas, and source contribution analyses for selected receptors.)

Final Report - 1995 Air Emissions Within the Southwest Wyoming Regional Modeling Domain
(Section 2 of Volume I The Southwest Wyoming Regional CALPUFF Air Quality Modeling Study - Final Report summarizes the emissions inventory used in the modeling effort. A more detailed description of the emission datasets is provided in this three-volume emissions report.)

Volume 1: CALPUFF Modeling Inventory
(Summarization of the techniques used to develop the CALPUFF emission input data files. The resulting modeling inventory is described and summarized along with a description of some of the quality assurance activities.)

Volume 2: Development of Industry and Facility Specific Inventories
(Description of the county-level annual/seasonal emissions inventory development using the "bottom-up" estimation approach.)

Volume 3: Appendices
(Appendix tables of source-by-source summaries that contain the detailed emission data from the work presented in Volume 1.)

SWWYTAF Project Files
(For a description of the contents of the SWWYTAF Project Files view the README file for the set of seven CDs.)

If you have questions pertaining to the SWWYTAF Project, contact Darla Potter at 307-777-7346 or e-mail at: dpotte@wyo.gov