| Table of Contents | Appendix A | Appendix B | Appendix C | Appendix D | Appendix E | Appendix F | Appendix G |
| Appendix H | Appendix I | Appendix J | Appendix K | Appendix L | Appendix M | Appendix N |

---

Appendix I — Air Quality Data

Carbon Monoxide And PM₁₀ Hot Spot Modeling

Introduction

Short-term air quality analyses were performed for carbon monoxide levels and concentrations of particulate matter which are equal to or less than 10 microns in diameter (commonly known as PM₁₀) on a roadway segment in order to assess the relative impact of the proposed transportation mitigation alternatives on ambient air quality in Yosemite Valley. The analyses were performed using the dispersion model CALINE3, which is the preferred U.S. Environmental Protection Agency (EPA) line-source Gaussian plume dispersion model that predicts the hourly average impacts of inert pollutants near roadways. The roadway geometry, worst-case meteorological parameters, traffic volumes, receptor positions, and emission factors were inputs to the model. The roadway link selection and traffic volumes definition were based on transportation studies conducted for the National Park Service (BRW 2000), and the carbon monoxide and PM₁₀ emission factors were integrated from the Yosemite Valley vehicle emissions database (EA 1996). Persistence factors were applied to the predicted maximum hourly average concentrations of carbon monoxide and PM₁₀ to estimate the maximum 8-hour average carbon monoxide concentrations and 24-hour average PM₁₀ concentrations. Moreover, the maximum concentrations imparted to traffic conditions of the proposed transportation alternatives were independently compared to those of the existing traffic conditions (No Action Alternative) in order to determine the amount and direction of changes in carbon monoxide and PM₁₀ concentrations. A roadway link representing the worst-case level of service (LOS) in Yosemite Valley was used for the analyses.

Model Description

CALINE3 is a line-source air quality model based on the Gaussian diffusion equation and employs a mixing zone concept to characterize pollutant dispersion over the roadway. The purpose of the model is to assess air quality impacts near transportation roadways. Using source strength, meteorology, and site geometry, the model predicts pollutant concentrations for receptors located within 150 meters of the roadway. CALINE3 divides individual roadway links into a series of elements from which incremental concentrations are computed and then summed to form a total concentration estimate for a particular receptor location. CALINE3 treats the region directly over the roadway as a zone of uniform emissions and turbulence. This is designated as the mixing zone and is defined as the region over the traveled way plus three meters on either side. The additional width accounts for the initial horizontal dispersion imparted to pollutants by the vehicle wake.

A link is defined as a straight segment of roadway having a constant width, height, traffic volume, and vehicle emission factor. The location of the link is specified by the endpoint coordinates of its centerline. The location of a receptor is specified in terms of X, Y, Z coordinates. The program automatically sums the contributions from each link to each receptor. After this is completed for all receptors, a background value may be added. Surface roughness is assumed to be uniform throughout the study area. The meteorological variables of atmospheric stability, wind speed, and wind direction are also taken as constant over the study area.

Pollutant deposition and settling are also taken into account in CALINE3. Deposition velocity is a measure of the rate at which a pollutant can be adsorbed or assimilated by a surface. It involves a molecular diffusive process through the laminar sublayer covering the surface. Settling velocity is the rate at which a particle falls with respect to its immediate surroundings. A composite vehicle emission factor in grams per vehicle-mile must be provided for each link.

Roadway Link Selection

Based on the levels of service and the traffic volume of the existing conditions, the Northside Drive segment from Yosemite Lodge to the park headquarters was selected for modeling. It is a two-way road segment for the existing traffic conditions and measures 1.13 miles long and 20 feet wide. This segment presents the worst-case traffic conditions. The associated levels of service are "D" and "E" for the a.m. and p.m. peak travel hours, respectively. The level of service quantifies the performance of a roadway section, and it ranges from "A" (best operating condition) to "F" (worst operating condition).

CALINE3 Inputs

Modeling Parameters

The modeling parameters define the averaging interval, the aerodynamic roughness coefficient, the settling and deposition velocities, the link/receptor geometry units, and the number of links and receptors. An averaging time of one hour was selected in order to study the short-term "hot spot" effect of carbon monoxide and PM₁₀. Moreover, the mandatory limit in CALINE3 is 120 minutes, which represents a reasonable limit of the power law approximation in the model formulation. A uniform aerodynamic roughness coefficient of 50 centimeters was selected since the valley road network lies on a relatively flat terrain with mixed vegetation and scattered buildings. This value corresponds to a rural, rolling, and lightly wooded terrain. The deposition velocity of PM₁₀ was estimated to be 0.5 centimeters per second (Zanneti 1990). CALINE3 assumes that the settling velocity is equal to the deposition velocity. Carbon monoxide deposition and settling rates are negligible. The link/receptor coordinates are expressed in meters, and 7 links and 14 receptors were defined (see Figure 1).

Link Geometry

The link geometry defines the link types, the endpoint coordinates, the link heights, and the mixing zone widths. The selected road segment was subdivided into seven straight segments whose locations are shown in Figure 1. An arbitrary X — Y (east — north) referential system was defined at about midpoint of the entire road segment. The links were numbered 1 to 7 from the east. All the links are at-grade, except link 4, which was defined as a bridge. The receptor locations are shown in Figure 1 as well. They are located very close to the link in order to simulate the short-term effects of the pollutants and to satisfy the assumptions of CALINE3. They are assigned the average breathing height of 1.8 meters. They are numbered 1 to 14 from the west. The mixing zone is 12.2 meters wide (20 feet travel-lane width plus 10 feet on each side) for Alternative 1 and 12.8 meters for the proposed alternatives (22 feet travel-lane width).

Link Activities

The link activities define the traffic volumes and the emission factors. The traffic volume data (in vehicles per hour) for the existing traffic conditions and the proposed transportation alternatives were obtained from National Park Service transportation studies (BRW 2000). Table I-1 presents the traffic volume data for the modeling segment. It was assumed that the total traffic volume remains constant on the entire road segment.

 

Modeling Conditions

The meteorological parameters needed to run the model these include wind speed and direction, atmospheric stability class, mixing height, and ambient background concentrations. In this study, the worst-case meteorological conditions and pollutant background concentrations that can be anticipated at the site were used. These parameters are summarized in Table I-3.

Carbon Monoxide Results

The maximum hourly average carbon monoxide concentrations predicted from the activities on the modeling road segment for the five transportation alternatives are presented in Tables I-4 and I-5. The 8-hour average carbon monoxide concentrations calculated by applying a persistence factor of 0.7 (EPA 1992) to the 1-hour average values also are presented in Tables I-4 and I-5. The spatially unpaired reductions relative to Alternative 1 in maximum carbon monoxide concentrations imparted to each of the proposed alternative are presented in Table I-4 and 5 as well. The maximum hourly average carbon monoxide concentrations (including the background concentration) vary from 3.50 parts per million to 5.10 parts per million for the a.m. peak travel hour and from 3.60 parts per million to 6.50 parts per million for the p.m. peak travel hour. The maximum 8-hour average carbon monoxide concentrations (including the background concentration) vary from 2.45 parts per million to 3.57 parts per million for the a.m. peak travel hour and from 2.52 parts per million to 4.55 parts per million for the p.m. peak travel hour. The reductions in generated maximum concentration vary from 9% to 76% for the a.m. peak travel hour and from 46% to 83% for the p.m. peak travel hour. Table I-4 and I-5 show that the p.m. peak travel hour represents the worst-case traffic and carbon monoxide air quality conditions. However, the reductions in air quality impacts during the p.m. peak travel hour are the highest for each alternative.

The data also indicate that the maximum carbon monoxide concentrations contributed by the traffic on the modeling road segment are below the federal and California 1-hour average standards of 35 parts per million and 20 parts per million, respectively and the 8-hour average federal and California carbon monoxide standard of 9 parts per million.

1. Calculated using the persistence factor 0.7
Percentages derived from 8-hour maximum concentrations without background.

PM₁₀ Results

The maximum hourly average PM₁₀ concentrations predicted from the activities on the modeled road segment for the five transportation alternatives are presented in Tables I-6 and I-7. The 24-hour average PM₁₀ concentrations calculated by applying a persistence factor of 0.4 (U.S. EPA 1992) to the 1-hour average values also are presented in Tables I-6 and I-7. The spatially unpaired reductions relative to Alternative 1 in maximum PM₁₀ concentrations imparted to each of the proposed alternative are presented in Tables I-6 and I-7 as well. The maximum 24-hour average PM₁₀ concentrations (including the background concentration) vary from 27.40 micrograms per cubic meter (µg/m³⁾ to 46.20 µg/m³) for the a.m. peak travel hour and from 28.20 m g/m³ to 64.20 m g/m³ for the p.m. peak travel hour. The reductions in generated maximum concentration vary from 11% to 75% for the a.m. peak travel hour and from 48% to 83% for the p.m. peak travel hour. Table I-6 and I-7 show that the p.m. peak travel hour represents the worst-case traffic and PM₁₀ air quality conditions. However, the reductions in air quality impacts during the p.m. peak travel hour are the highest for each alternative.

The data also indicate that the maximum 24-hour average PM₁₀ concentrations contributed by the modeled road segment traffic are below the federal 24-hour average standard of 150 m g/m³ for all alternatives, but exceeds the California 24-hour standard of 50 m g/m³ for the evening peak travel hour for the No Action Alternative (Alternative 1).

1. Calculated with a persistence factor of 0.4
Percentages derived from 24-hour maximum concentrations without background.

Conclusion

CALINE3 was used to study the short-term hot spot effects of carbon monoxide and PM₁₀ pollutants for five transportation alternatives in Yosemite Valley. The dispersion modeling was applied to the Northside Drive roadway segment from Yosemite Lodge to park headquarters, which represents the worst-case operating conditions. The results of the modeling show that the 1-hour and 8-hour average maximum concentrations of carbon monoxide are below the federal standards. The 24-hour average PM₁₀ concentrations are below the federal standard, but exceed the California standard for Alternative 1, the No Action Alternative for the evening peak travel hour. The reductions in maximum concentrations from the proposed alternatives relative to the No Action Alternative vary from 9.5% to 83% for carbon monoxide and from 11% to 83% for PM₁₀.

---

| Table of Contents | Appendix A | Appendix B | Appendix C | Appendix D | Appendix E | Appendix F | Appendix G |
| Appendix H | Appendix I | Appendix J | Appendix K | Appendix L | Appendix M | Appendix N |

Yosemite National Park Home Page http://www.nps.gov File created/updated Yosemite National Park Web Manager