Document DM6vXB5pea9BRwa2Ypx0zY70O

3.2.1 Paved Roads 13.2.1.1 General Particulate emissions occur whenever vehicles travel over a paved surface such as a road or parking lot. Particulate emissions from paved roads are due to direct emissions from vehicles in the form of exhaust, brake wear and tire wear emissions and resuspension of loose material on the road surface. In general terms, resuspended particulate emissions from paved roads originate from, and result in the depletion of, the loose material present on the surface (i.e., the surface loading). In turn, that surface loading is continuously replenished by other sources. At industrial sites, surface loading is replenished by spillage of material and trackout from unpaved roads and staging areas. Figure 13.2.1-1 illustrates several transfer processes occurring on public streets. Various field studies have found that public streets and highways, as well as roadways at industrial facilities, can be major sources of the atmospheric particulate matter within an area.1-9 Of particular interest in many parts of the United States are the increased levels of emissions from public paved roads when the equilibrium between deposition and removal processes is upset. This situation can occur for various reasons, including application of granular materials for snow and ice control, mud/dirt carryout from construction activities in the area, and deposition from wind and/or water erosion of surrounding unstabilized areas. In the absence of continuous addition of fresh material (through localized trackout or application of antiskid material), paved road surface loading should reach an equilibrium value in which the amount of material resuspended matches the amount replenished. The equilibrium surface loading value depends upon numerous factors. It is believed that the most important factors are: mean speed of vehicles traveling the road; the average daily traffic (ADT); the number of lanes and ADT per lane; the fraction of heavy vehicles (buses and trucks); and the presence/absence of curbs, storm sewers and parking lanes.10 The particulate emission factors presented in the previous version of this section of AP-42, dated October 2002, implicitly included the emissions from vehicles in the form of exhaust, brake wear, and tire wear as well as resuspended road surface material. EPA included these sources in the emission factor equation for paved roads since the field testing data used to develop the equation included both the direct emissions from vehicles and emissions from resuspension of road dust. This version of the paved road emission factor equation only estimates particulate emissions from resuspended road surface material 28. The particulate emissions from vehicle exhaust, brake wear, and tire wear are now estimated separately using EPA's MOBILE6.2 27. This approach eliminates the possibility of double counting emissions. Double counting results when employing the previous version of the emission factor equation in this section and MOBILE6.2 to estimate particulate emissions from vehicle traffic on paved roads. It also incorporates the decrease in exhaust emissions that has occurred since the paved road emission factor equation was developed. The previous version of the paved road emission factor equation includes estimates of emissions from exhaust, brake wear, and tire wear based on emission rates for vehicles in the 1980 calendar year fleet. The amount of PM released from vehicle exhaust has decreased since 1980 due to lower new vehicle emission standards and changes in fuel characteristics. 12/03 Miscellaneous Sources 13.2.1-1 13.2.1.2 Emissions And Correction Parameters Dust emissions from paved roads have been found to vary with what is termed the "silt loading" present on the road surface as well as the average weight of vehicles traveling the road. The term silt loading (sL) refers to the mass of silt-size material (equal to or less than 75 micrometers [pm] in physical diameter) per unit area of the travel surface. The total road surface dust loading consists of loose material that can be collected by broom sweeping and vacuuming of the traveled portion of the paved road. The silt fraction is determined by measuring the proportion of the loose dry surface dust that passes through a 200-mesh screen, using the ASTM-C-136 method. Silt loading is the product of the silt fraction and the total loading, and is abbreviated "sL". Additional details on the sampling and analysis of such material are provided in AP-42 Appendices C.1 and C.2. The surface sL provides a reasonable means of characterizing seasonal variability in a paved road emission inventory. In many areas of the country, road surface loadings 11-21 are heaviest during the late winter and early spring months when the residual loading from snow/ice controls is greatest. As noted earlier, once replenishment of fresh material is eliminated, the road surface loading can be expected to reach an equilibrium value, which is substantially lower than the late winter/early spring values. 13.2.1-2 EMISSION FACTORS 12/03 12/03 Miscellaneous Sources 13.2.1-3 Figure 13.2.1-1. Deposition and removal processes. 13.2.1.3 Predictive Emission Factor Equations 10 The quantity of particulate emissions from resuspension of loose material on the road surface due to vehicle travel on a dry paved road may be estimated using the following empirical expression: xE = k( sL^ 0-65 (wV'5 C V2J V3j (1) where: E = particulate emission factor (having units matching the units of k), k = particle size multiplier for particle size range and units of interest (see below), sL = road surface silt loading (grams per square meter) (g/m2), W = average weight (tons) of the vehicles traveling the road, and C = emission factor for 1980's vehicle fleet exhaust, brake wear and tire wear. It is important to note that Equation 1 calls for the average weight of all vehicles traveling the road. For example, if 99 percent of traffic on the road are 2 ton cars/trucks while the remaining 1 percent consists of 20 ton trucks, then the mean weight "W" is 2.2 tons. More specifically, Equation 1 is not intended to be used to calculate a separate emission factor for each vehicle weight class. Instead, only one emission factor should be calculated to represent the "fleet" average weight of all vehicles traveling the road. The particle size multiplier (k) above varies with aerodynamic size range as shown in Table 13.2.1-1. To determine particulate emissions for a specific particle size range, use the appropriate value of k shown in Table 13.2.1-1. The emission factors for the exhaust, brake wear and tire wear of a 1980's vehicle fleet (C) was obtained from EPA's MOBILE6.2 model 28. The emission factor also varies with aerodynamic size range Table 13.2-1.1. PARTICLE SIZE MULTIPLIERS FOR PAVED ROAD EQUATION Size range3 PM-2.5c PM-10 PM-15 PM-30d g/VKT 1.1 4.6 5.5 24 Particle Size Multiplier kb g/VMT 1.8 7.3 9.0 38 lb/VMT 0.0040 0.016 0.020 0.082 a Refers to airborne particulate matter (PM-x) with an aerodynamic diameter equal to or less than x micrometers. b Units shown are grams per vehicle kilometer traveled (g/VKT), grams per vehicle mile traveled (g/VMT), and pounds per vehicle mile traveled (lb/VMT). The multiplier k includes unit conversions to produce emission factors in the units shown for the indicated size range from the mixed units required in Equation 1. c Ratio of PM-2.5 to PM-10 taken from Reference 22. d PM-30 is sometimes termed "suspendable particulate" (SP) and is often used as a surrogate for TSP. 13.2.1-4 EMISSION FACTORS 12/03 as shown in Table 13.2.1-2. Table 13.2.1-2. EMISSION FACTOR FOR 1980'S VEHICLE FLEET EXHAUST, BRAKE WEAR AND TIRE WEAR Particle Size Rangea PM2.5 PM10 PM15 PM30c C, Emission Factor for Exhaust, Brake Wear and Tire Wearb g/VMT g/VKT lb/VMT 0.1617 0.2119 0.2119 0.1005 0.1317 0.1317 0.00036 0.00047 0.00047 0.2119 0.1317 0.00047 a Refers to airborne particulate matter (PM-x) with an aerodynamic diameter equal to or less than x micrometers. b Units shown are grams per vehicle kilometer traveled (g/VKT), grams per vehicle mile traveled (g/VMT), and pounds per vehicle mile traveled (lb/VMT). c PM-30 is sometimes termed "suspendable particulate" (SP) and is often used as a surrogate for TSP. Equation 1 is based on a regression analysis of numerous emission tests, including 65 tests for PM-10.10 Sources tested include public paved roads, as well as controlled and uncontrolled industrial paved roads. All sources tested were of freely flowing vehicles traveling at constant speed on relatively level roads. No tests of "stop-and-go" traffic or vehicles under load were available for inclusion in the data base. The equations retain the quality rating of A (B for PM-2.5), if applied within the range of source conditions that were tested in developing the equation as follows: Silt loading: 0.03 - 400 g/m2 0.04 - 570 grains/square foot (ft2) Mean vehicle weight: 1.8 - 38 megagrams (Mg) 2.0 - 42 tons Mean vehicle speed: 16 - 88 kilometers per hour (kph) 10 - 55 miles per hour (mph) Note: There may be situations where low silt loading and/or low average weight will yield calculated negative emissions from equation 1. If this occurs, the emissions calculated from equation 1 should be set to zero. Users are cautioned that application of equation 1 outside of the range of variables and operating conditions specified above, e.g., application to roadways or road networks with speeds below 10 mph and with stop-and-go traffic, will result in emission estimates with a higher level of uncertainty. In these situations, users are encouraged to consider alternative methods that are 12/03 Miscellaneous Sources 13.2.1-5 equally or more plausible in light of local emissions data and/or ambient concentration or compositional data. To retain the quality rating for the emission factor equation when it is applied to a specific paved road, it is necessary that reliable correction parameter values for the specific road in question be determined. With the exception of limited access roadways, which are difficult to sample, the collection and use of site-specific silt loading (sL) data for public paved road emission inventories are strongly recommended. The field and laboratory procedures for determining surface material silt content and surface dust loading are summarized in Appendices C.1 and C.2. In the event that site-specific values cannot be obtained, an appropriate value for a paved public road may be selected from the values in Table 13.2.1-3, but the quality rating of the equation should be reduced by 2 levels. Also, recall that Equation 1 refers to emissions due to freely flowing (not stop-and-go) traffic at constant speed on level roads. Equation 1 may be extrapolated to average uncontrolled conditions (but including natural mitigation) under the simplifying assumption that annual (or other long-term) average emissions are inversely proportional to the frequency of measurable (> 0.254 mm [ 0.01 inch]) precipitation by application of a precipitation correction term. The precipitation correction term can be applied on a daily or an hourly basis 26. For the daily basis, Equation 1 becomes: where k, sL, W, and C are as defined in Equation 1 and Eext = annual or other long-term average emission factor in the same units as k, P = number of "wet" days with at least 0.254 mm (0.01 in) of precipitation during the averaging period, and N = number of days in the averaging period (e.g., 365 for annual, 91 for seasonal, 30 for monthly). Note that the assumption leading to Equation 2 is based on analogy with the approach used to develop long-term average unpaved road emission factors in Section 13.2.2. However, Equation 2 above incorporates an additional factor of "4" in the denominator to account for the fact that paved roads dry more quickly than unpaved roads and that the precipitation may not occur over the complete 24-hour day. For the hourly basis, equation 1 becomes: 1.2 P C 1- N (3) where k, sL, and W, and C are as defined in Equation 1 and 13.2.1-6 EMISSION FACTORS 12/03 Eext = annual or other long-term average emission factor in the same units as k, P = number of hours with at least 0.254 mm (0.01 in) of precipitation during the averaging period, and N = number of hours in the averaging period (e.g., 8760 for annual, 2124 for season 720 for monthly). Note: In the hourly moisture correction term (1-1.2P/N) for equation 3, the 1.2 multiplier is applied to account for the residual mitigative effect of moisture. For most applications, this equation will produce satisfactory results. However, if the time interval for which the equation is applied is short, e.g., for one hour or one day, the application of this multiplier makes it possible for the moisture correction term to become negative. This will result in calculated negative emissions which is not realistic. Users should expand the time interval to include sufficient "dry" hours such that negative emissions are not calculated. For the special case where this equation is used to calculate emissions on an hour by hour basis, such as would be done in some emissions modeling situations, the moisture correction term should be modified so that the moisture correction "credit" is applied to the first hours following cessation of precipitation. In this special case, it is suggested that this 20% "credit" be applied on a basis of one hour credit for each hour of precipitation up to a maximum of 12 hours. Note that the assumption leading to Equation 3 is based on analogy with the approach used to develop long-term average unpaved road emission factors in Section 13.2.2. Figure 13.2.1-2 presents the geographical distribution of "wet" days on an annual basis for the United States. Maps showing this information on a monthly basis are available in the Climatic Atlas ofthe United States23 . Alternative sources include other Department of Commerce publications (such as local climatological data summaries). The National Climatic Data Center (NCDC) offers several products that provide hourly precipitation data. In particular, NCDC offers Solar and Meteorological Surface Observation Network 1961-1990 (SAMSON) CD-ROM, which contains 30 years worth of hourly meteorological data for first-order National Weather Service locations. Whatever meteorological data are used, the source of that data and the averaging period should be clearly specified. It is emphasized that the simple assumption underlying Equations 2 and 3 has not been verified in any rigorous manner. For that reason, the quality ratings for Equations 2 and 3 should be downgraded one letter from the rating that would be applied to Equation 1. 12/03 Miscellaneous Sources 13.2.1-7 13.2.1-8 EMISSION FACTORS 12/03 Figure 13.2.1-2. Mean number of days with 0.01 inch or more of precipitation in the United States. Table 13.2.1-3 presents recommended default silt loadings for normal baseline conditions and for wintertime baseline conditions in areas that experience frozen precipitation with periodic application of antiskid material24. The winter baseline is represented as a multiple of the non winter baseline, depending on the ADT value for the road in question. As shown, a multiplier of 4 is applied for low volume roads (< 500 ADT) to obtain a wintertime baseline silt loading of 4 X 0.6 = 2.4 g/m2. Table 13.2.1-3. Ubitiguous Silt Loading Default Values with Hot Spot Contributions rom Anti-Skid Abrasives (g/m2) ADT Category < 500 500-5,000 5,000-10,000 > 10,000 Ubiquitous Baseline g/m2 0.6 0.2 0.06 0.03 0.015 limited access Ubitiguous Winter Baseline Multiplier during months with frozen precipitation X4 X3 X2 X1 Initial peak additive contribution from application of antiskid abrasive (g/m2) 2 2 2 2 Days to return to baseline conditions 7 (assume linear decay) 3 1 0.5 It is suggested that an additional (but temporary) silt loading contribution of 2 g/m2 occurs with each application of antiskid abrasive for snow/ice control. This was determined based on a typical application rate of 500 lb per lane mile and an initial silt content of 1 % silt content. Ordinary rock salt and other chemical deicers add little to the silt loading, because most of the chemical dissolves during the snow/ice melting process. To adjust the baseline silt loadings for mud/dirt trackout, the number of trackout points is required. It is recommended that in calculating PM-10 emissions, six additional miles of road be added for each active trackout point from an active construction site, to the paved road mileage of the specified category within the county. In calculating PM-2.5 emissions, it is recommended that three additional miles of road be added for each trackout point from an active construction site. It is suggested the number of trackout points for activities other than road and building construction areas be related to land use. For example, in rural farming areas, each mile of paved road would have a specified number of trackout points at intersections with unpaved roads. This value could be estimated from the unpaved road density (mi/sq. mi.). The use of a default value from Table 13.2.1-3 should be expected to yield only an orderof-magnitude estimate of the emission factor. Public paved road silt loadings are dependent 12/03 Miscellaneous Sources 13.2.1-9 upon: traffic characteristics (speed, ADT, and fraction of heavy vehicles); road characteristics (curbs, number of lanes, parking lanes); local land use (agriculture, new residential construction) and regional/seasonal factors (snow/ice controls, wind blown dust). As a result, the collection and use of site-specific silt loading data is highly recommended. In the event that default silt loading values are used, the quality ratings for the equation should be downgraded 2 levels. Limited access roadways pose severe logistical difficulties in terms of surface sampling, and few silt loading data are available for such roads. Nevertheless, the available data do not suggest great variation in silt loading for limited access roadways from one part of the country to another. For annual conditions, a default value of 0.015 g/m2 is recommended for limited access roadways.9,22 Even fewer of the available data correspond to worst-case situations, and elevated loadings are observed to be quickly depleted because of high traffic speeds and high ADT rates. A default value of 0.2 g/m2 is recommended for short periods of time following application of snow/ice controls to limited access roads.22 The limited data on silt loading values for industrial roads have shown as much variability as public roads. Because of the variations of traffic conditions and the use of preventive mitigative controls, the data probably do not reflect the full extent of the potential variation in silt loading on industrial roads. However, the collection of site specific silt loading data from industrial roads is easier and safer than for public roads. Therefore, the collection and use of site-specific silt loading data is preferred and is highly recommended. In the event that site-specific values cannot be obtained, an appropriate value for an industrial road may be selected from the mean values given in Table 13.2.1-4, but the quality rating of the equation should be reduced by 2 levels. 13.2.1-10 EMISSION FACTORS 12/03 12/03 Table 13.2.1-4 (Metric And English Units). TYPICAL SILT CONTENT AND LOADING VALUES FOR PAVED ROADS AT INDUSTRIAL FACILITIES a Miscellaneous Sources Industry No. Of Sites No. Of Sample s Silt Content (%) Range Mean No. Of Travel Lanes Total Loading x 1 0!3 Silt Loading (g/m2) Range Mean Unitsb Range Mean Copper smelting 1 3 15.4-21.7 19.0 2 12.9-19.5 15.9 kg/km 188-400 292 45.8-69.2 55.4 lb/mi Iron and steel production 9 48 1.1-35.7 12.5 2 0.006-4.77 0.495 kg/km 0.09-79 9.7 0.020-16.9 1.75 lb/mi Asphalt batching 1 3 2.6-4.6 3.3 1 12.1-18.0 14.9 kg/km 76-193 120 43.0-64.0 52.8 lb/mi Concrete batching 1 3 5.2-6.0 5.5 2 1.4-1.8 1.7 kg/km 11-12 12 5.0-6.4 5.9 lb/mi Sand and gravel processing 1 3 6.4-7.9 7.1 1 2.8-5.5 3.8 kg/km 53-95 70 9.9-19.4 13.3 lb/mi Municipal solid waste landfill 2 7 ---- 2 ---- -- 1.1-32.0 7.4 Quarry 1 6 ---- 2 ---- -- 2.4-14 8.2 a References 1-2,5-6,11-13. Values represent samples collected from industrial roads. Public road silt loading values are presented in Table-13.2.1-2. Dashes indicate information not available. b Multiply entries by 1000 to obtain stated units; kilograms per kilometer (kg/km) and pounds per mile (lb/mi). 13.2.1-11 13.2.1.4 Controls6,25 Because of the importance of the silt loading, control techniques for paved roads attempt either to prevent material from being deposited onto the surface (preventive controls) or to remove from the travel lanes any material that has been deposited (mitigative controls). Covering of loads in trucks, and the paving of access areas to unpaved lots or construction sites, are examples of preventive measures. Examples of mitigative controls include vacuum sweeping, water flushing, and broom sweeping and flushing. Actual control efficiencies for any of these techniques can be highly variable. Locally measured silt loadings before and after the application of controls is the preferred method to evaluate controls. It is particularly important to note that street sweeping of gutters and curb areas may actually increase the silt loading on the traveled portion of the road. Redistribution of loose material onto the travel lanes will actually produce a short-term increase in the emissions. In general, preventive controls are usually more cost effective than mitigative controls. The cost-effectiveness of mitigative controls falls off dramatically as the size of an area to be treated increases. The cost-effectiveness of mitigative measures is also unfavorable if only a short period of time is required for the road to return to equilibrium silt loading condition. That is to say, the number and length of public roads within most areas of interest preclude any widespread and routine use of mitigative controls. On the other hand, because of the more limited scope of roads at an industrial site, mitigative measures may be used quite successfully (especially in situations where truck spillage occurs). Note, however, that public agencies could make effective use of mitigative controls to remove sand/salt from roads after the winter ends. Because available controls will affect the silt loading, controlled emission factors may be obtained by substituting controlled silt loading values into the equation. (Emission factors from controlled industrial roads were used in the development of the equation.) The collection of surface loading samples from treated, as well as baseline (untreated), roads provides a means to track effectiveness of the controls over time. 13.2.1.5 Changes since Fifth Edition The following changes were made since the publication of the Fifth Edition of AP-42: 1) The particle size multiplier was reduced by approximately 55% as a result of emission testing specifically to evaluate the PM-2.5 component of the emissions. 2) Default silt loading values were included in Table 13.2.1-2 replacing the Tables and Figures containing silt loading statistical information. 3) Editorial changes within the text were made indicating the possible causes of variations in the silt loading between roads within and among different locations. The uncertainty of using the default silt loading value was discussed. 13.2.1-12 EMISSION FACTORS 12/03 4) Section 13.2.1.1 was revised to clarify the role of dust loading in resuspension. Additional minor text changes were made. 5) Equations 2 and 3, Figure 13.2.1-2, and text were added to incorporate natural mitigation into annual or other long-term average emission factors. 6) The emission factor equation was adjusted to remove the component of particulate emissions from exhaust, brake wear, and tire wear. The parameter C in the new equation varies with aerodynamic size range of the particulate matter. Table 13.2.1-2 was added to present the new coefficients. 7) The default silt loading values in Table 13.2.1-3 were revised to incorporate the results from a recent analysis of silt loading data. 8) References were rearranged and renumbered. References For Section 13.2.1 1. D. R. Dunbar, Resuspension OfParticulate Matter, EPA-450/2-76-031, U. S. Environmental Protection Agency, Research Triangle Park, NC, March 1976. 2. R. Bohn, et al., Fugitive Emissions From Integrated Iron And Steel Plants, EPA-600/2-78-050, U. S. Environmental Protection Agency, Cincinnati, OH, March 1978. 3. C. Cowherd, Jr., et al., Iron And Steel Plant Open Dust Source Fugitive Emission Evaluation, EPA-600/2-79-103, U. S. Environmental Protection Agency, Cincinnati, OH, May 1979. 4. C. Cowherd, Jr., et al., Quantification OfDust Entrainment From Paved Roadways, EPA-450/3-77-027, U. S. Environmental Protection Agency, Research Triangle Park, NC, July 1977. 5. Size Specific Particulate Emission Factors For Uncontrolled Industrial And Rural Roads, EPA Contract No. 68-02-3158, Midwest Research Institute, Kansas City, MO, September 1983. 6. T. Cuscino, Jr., et al., Iron And Steel Plant Open Source Fugitive Emission Control Evaluation, EPA-600/2-83-110, U. S. Environmental Protection Agency, Cincinnati, OH, October 1983. 7. J. P. Reider, Size-specific Particulate Emission Factors For Uncontrolled Industrial And Rural Roads, EPA Contract 68-02-3158, Midwest Research Institute, Kansas City, MO, September 1983. 12/03 Miscellaneous Sources 13.2.1-13 8. C. Cowherd, Jr., and P. J. Englehart, Paved Road Particulate Emissions, EPA-600/7-84-077, U. S. Environmental Protection Agency, Cincinnati, OH, July 1984. 9. C. Cowherd, Jr., and P. J. Englehart, Size Specific Particulate Emission Factors For Industrial And Rural Roads, EPA-600/7-85-038, U. S. Environmental Protection Agency, Cincinnati, OH, September 1985. 10. Emission Factor Documentation For AP-42, Sections 11.2.5 and 11.2.6 -- Paved Roads, EPA Contract No. 68-D0-0123, Midwest Research Institute, Kansas City, MO, March 1993. 11. Evaluation Of Open Dust Sources In The Vicinity OfBuffalo, New York, EPA Contract No. 68-02-2545, Midwest Research Institute, Kansas City, MO, March 1979. 12. PM-10 Emission Inventory OfLandfills In The Lake Calumet Area, EPA Contract No. 68-02-3891, Midwest Research Institute, Kansas City, MO, September 1987. 13. Chicago Area Particulate Matter Emission Inventory -- Sampling And Analysis, Contract No. 68-02-4395, Midwest Research Institute, Kansas City, MO, May 1988. 14. Montana Street Sampling Data, Montana Department Of Health And Environmental Sciences, Helena, MT, July 1992. 15. Street Sanding Emissions And Control Study, PEI Associates, Inc., Cincinnati, OH, October 1989. 16. Evaluation OfPM-10 Emission Factors For Paved Streets, Harding Lawson Associates, Denver, CO, October 1991. 17. Street Sanding Emissions And Control Study, RTP Environmental Associates, Inc., Denver, CO, July 1990. 18. Post-storm Measurement Results -- Salt Lake County Road Dust Silt Loading Winter 1991/92 Measurement Program, Aerovironment, Inc., Monrovia, CA, June 1992. 19. Written communication from Harold Glasser, Department of Health, Clark County (NV). 20. PM-10 Emissions Inventory Data For The Maricopa And Pima Planning Areas, EPA Contract No. 68-02-3888, Engineering-Science, Pasadena, CA, January 1987. 21. Characterization OfPM-10 Emissions From Antiskid Materials Applied To Ice- And SnowCovered Roadways, EPA Contract No. 68-D0-0137, Midwest Research Institute, Kansas City, MO, October 1992. 22. Fugitive Particulate Matter Emissions, EPA Contract No. 68-D2-0159, Work Assignment No. 4-06, Midwest Research Institute, Kansas City, MO, April 1997. 13.2.1-14 EMISSION FACTORS 12/03 23. Climatic Atlas Of The United States, U.S. Department of Commerce, Washington, D.C., June 1968. 24. C. Cowherd, Jr., et al., Improved Activity Levels for National Emission Inventories of Fugitive Dust from Paved and Unpaved Roads, Presented at the 11th International Emission Inventory Conference, Atlanta, Georgia, April 2002. 25. C. Cowherd, Jr., et al., Control Of Open Fugitive Dust Sources, EPA-450/3-88-008, U. S. Environmental Protection Agency, Research Triangle Park, NC, September 1988. 26. Written communication (Technical Memorandum) from G. Muleski, Midwest Research Institute, Kansas City, MO, to B. Kuykendal, U. S. Environmental Protection Agency, Research Triangle Park, NC, September 27, 2001. 27. EPA, 2002b. MOBILE6 User Guide, United States Environmental Protection Agency, Office of Transportation and Air Quality. EPA420-R-02-028, October 2002. 28. Written communication (Technical Memorandum) from P. Hemmer, E.H. Pechan & Associates, Inc., Durham, NC to B. Kuykendal, U. S. Environmental Protection Agency, Research Triangle Park, NC, August, 21, 2003. 12/03 Miscellaneous Sources 13.2.1-15