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Acknowledgments US Department of Transportation - BTS

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TABLES 4-45, 4-46, 4-47, 4-48, 4-49, 4-50. Estimates <strong>of</strong> National Emissions <strong>of</strong> Carbon Monoxide, NitrogenOxides, Volatile Organic Compounds, Particular Matter, Sulfur DioxideEmissions by sector and source are estimated using various models and calculation techniques and are based on anumber <strong>of</strong> assumptions and on data that vary in precision and reliability. The methods used are theoretically sound,the assumptions are reasonable, but the data vary in quality, and no formal analysis <strong>of</strong> the accuracy <strong>of</strong> theseestimates has been performed.Carbon Monoxide (CO), Nitrogen Oxides (NOx), and Volatile Organic Compounds (VOCs)Highway vehicle emissions <strong>of</strong> CO, NOx, and VOC are generated by the U.S. Environmental Protection Agency's(EPA's) Mobile Source Emissions Factor Model (MOBILE), which uses per-mile vehicle emissions factors and vehicletravel (vehicle-miles) to calculate county-level emissions. Emissions rates are then adjusted based on fuelcharacteristics, vehicle fleet composition, emissions control measures, average vehicle speed, and other factors thatcan affect emissions. (Emissions rates used in MOBILE are based on vehicle certification tests, emissions standards,and in-use vehicle tests and are updated approximately every three years.) The U.S. <strong>Department</strong> <strong>of</strong> <strong>Transportation</strong>,Federal Highway Administration's Highway Performance Monitoring System is the source <strong>of</strong> vehicle travel estimatesused in the model. Although the methodology for this survey data is sound and well documented, analyses haveshown that individual states vary in how rigorously they follow the established sampling guidelines.The non-highway vehicle emissions are calculated annually by running EPA's NONROAD model for all categoriesexcept aircraft, commercial marine vessels, and railroads, which are calculated via emission factors and relevantactivity data. Inputs to the NONROAD model include average temperatures, Reid vapor pressure, fuel usageprograms and controls.Particulate Matter Under 10 Microns (PM-10) and 2.5 Microns (PM-2.5) in SizeHighway vehicle emissions are estimated using the U.S. Environments Protection Agency's PART model, whichestimates emissions factors for exhaust emissions and brake and tire wear by vehicle type. Exhaust emissionsfactors are based on certification tests, while brake wear (per vehicle) and tire wear (per tire) are assumed values,which are constant over all years. Per-mile emissions factors are multiplied by vehicle travel (vehicle-miles) andadjusted to account for other factors that effect exhaust emissions (e.g., fuel composition, weather, etc.). The U.S.<strong>Department</strong> <strong>of</strong> <strong>Transportation</strong>, Federal Highway Administration's Highway Performance Monitoring System is thesource <strong>of</strong> vehicle-miles <strong>of</strong> travel (VMT) estimates used in the model. While the methodology for this survey data issound and well documented, analyses have shown that individual states vary in how rigorously they follow theestablished sampling guidelines.Fugitive dust estimates for paved and unpaved roads are calculated by multiplying VMT on each type <strong>of</strong> road byemissions factors for each vehicle type and road type.The non-highway vehicle emissions are calculated annually by running EPA's NONROAD model for all categoriesexcept aircraft, commercial marine vessels, and railroads, which are calculated via emission factors and relevantactivity data. Inputs to the NONROAD model include average temperatures, Reid vapor pressure, fuel usageprograms and controls.Sulfur Dioxide (SO2)Highway vehicle SO2 emissions are estimated by multiplying vehicle travel (for each vehicle type and highway type)by an emissions factor reflecting each vehicle type and highway type. Highway SO2 emissions factors are based onvehicle type and model year, sulfur content <strong>of</strong> fuel by type and year, fuel density by fuel type, and vehicle fuelefficiency by type and model year.In general, estimates for non-highway vehicles are calculated based on fuel consumption and sulfur content <strong>of</strong> fuel,though other factors may be considered.Lead

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