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PRO*^ 2020 National Emissions Inventory Technical Support Document: Solvents - Consumer and Commercial: Asphalt Paving ------- ------- EP A-454/R-23 -001 ee March 2023 2020 National Emissions Inventory Technical Support Document: Solvents - Consumer and Commercial: Asphalt Paving U.S. Environmental Protection Agency Office of Air Quality Planning and Standards Air Quality Assessment Division Research Triangle Park, NC ------- Contents List of Tables i 31 Solvents - Consumer and Commercial: Asphalt Paving 31-1 31.1 Sector Descriptions and Overview 31-1 31.2 EPA-developed estimates 31-2 31.2.1.1 Activity Data 31-2 31.2.1.2 Allocation Procedure 31-4 31.2.1.3 Emission Factors 31-5 31.2.1.4 Controls 31-6 31.2.1.5 Emissions 31-6 31.2.1.6 Sample Calculations 31-6 31.2.2 Improvements/Changes in the 2020 NEI 31-7 31.2.2.1 Puerto Rico and U.S. Virgin Islands 31-7 31.3 References 31-7 List of Tables Table 31-1: Asphalt Paving SCCs in the 2020 NEI 31-2 Table 31-2: Sample calculations for emulsified asphalt usage 31-6 l ------- 31 Solvents - Consumer and Commercial: Asphalt Paving 31.1 Sector Descriptions and Overview Liquid asphalt is a petroleum-derived substance used in paving applications, such as the construction of roads, parking lots, driveways, and airport runways, as well as non-paving applications, such as the manufacturing of roofing shingles. While liquid asphalt can be found in natural deposits, most is produced from crude oil. Vacuum distillation separates components of crude oil based on boiling point. Products generated from this process include naptha, gasoline, diesel, and liquid asphalt, the last of which has a boiling point greater than 500 °C. As a result, most volatile, light fractions of organics are separated from liquid asphalt during distillation and prior to use. In paving applications, liquid asphalt can be applied cold or heated. If applied cold, additional components must be added to lower the viscosity of the material, which allows it to be spread upon a surface (e.g., roadway surface). Cutback asphalt (SCC: 2461021000) is a cold application process that involves mixing the liquid asphalt with petroleum solvents (e.g., naphtha, kerosene, fuel oil, diesel, etc.). Following application, these higher volatility solvents evaporate, leaving the asphalt in place. Due to this increased organic emissions potential, cutback asphalts have grown less common overtime and this process now constitutes ~1% of liquid asphalt is use [ref 1], Emulsified asphalt (SCC: 2461022000) is a separate cold application process that utilizes water-based solvents and an emulsifying agent. The result is a stable liquid suspension with asphalt globules. Following application, the additives evaporate and leave the asphalt in place. In contrast to cutback asphalts, emulsified asphalts have become more common in recent years and ~10% of liquid asphalt is now used in these applications. Liquid asphalt can also be applied heated, which both lowers the viscosity of the material and minimizes the need for added solvents. Hot-mix asphalt application (SCC: 2461025100), which is the traditional method for asphalt pavement production, involves combining the liquid asphalt with aggregate at a hot- mix plant and heating the mixture to +150 °C. The mixture is then hauled to the usage site heated, where it is placed, compacted, and ambiently cooled. This process does not require any solvent additions. Warm-mix asphalt application (SCC: 2461025200) is a more recent technology that enables asphalt pavement production to occur at 20 - 40 °C cooler temperatures than hot-mix asphalt application. Warm-mix asphalt applications at reduced temperatures now constitute ~18% of asphalt paving applications [ref 2], These lower production temperatures promote energy savings through reductions in fuel use and lower emissions at the hot-mix plant. To reduce the viscosity of the liquid asphalt in warm- mix applications, water, water-bearing minerals, chemicals, waxes, organic additives, or a combination of technologies must be added [ref 3], While heated applications processes represent most liquid asphalt paving applications, it has historically been assumed that emissions were sparse due to the removal of the more volatile organics during distillation. Recent research has demonstrated that less volatile organic vapors from liquid asphalt do evaporate at temperatures associated with hot-mix application (~140 °C), warm-mix application (120 °C), and post-application, or "in-use" temperatures [ref 4], Emission during the "in-use" period diffuse from the pavement over time following application. Starting with the 2020 NEI, EPA will estimate emissions from cutback, emulsified, hot-mix and warm-mix asphalt use. 31-1 ------- The table below notes all SCCs covered in this source category and the SCCs for which the EPA generates default emissions. Table 31-1: Asphalt Paving SCCs in the 2020 NEI see see Level 1 SCC Level 2 SCC Level 3 SCC Level 4 EPA 2461021000 Solvent Utilization Misc Non- industrial: Commercial Cutback Asphalt Total: All Solvent Types X 2461022000 Solvent Utilization Misc Non- industrial: Commercial Emulsified Asphalt Total: All Solvent Types X 2461025000 Solvent Utilization Miscellaneous Non-industrial: Commercial Asphalt Paving: Hot and Warm- mix Hot and Warm- mix Total: All Solvent Types 2461025100 Solvent Utilization Miscellaneous Non-industrial: Commercial Asphalt Paving: Hot and Warm- mix Hot-mix Total: All Solvent Types X 2461025200 Solvent Utilization Miscellaneous Non-industrial: Commercial Asphalt Paving: Hot and Warm- mix Warm-mix Total: All Solvent Types X 2461026000 Solvent Utilization Miscellaneous Non-industrial: Commercial Asphalt Paving: Road Oil Total: All Solvent Types 31.2 EPA-developed estimates Usage of liquid asphalt at the state-level for each process is calculated and subsequently allocated to the county-level using estimated vehicle miles traveled on paved roads. Emission factors consider both application and in-use processes. Net county-level emissions are quantified by multiplying the SCC- specific liquid asphalt usage by SCC-specific emission factors. The sources of data, calculation of state- level, SCC-specific usage results, allocation of state-level usage to the county-level, emission factors, and emission estimates are all discussed in subsequent sections. 31.2.1 Activity Data Activity data for these sources are the amount of liquid asphalt used in each process. Each year, the Asphalt Institute releases an asphalt usage survey for the Unites States and Canada that reflects usage among their membership [ref 1], The Asphalt Institute estimates that their membership captures 90% of the United States market and the total asphalt usage they report (~22.5 million tons) for 2020 is consistent with the asphalt and road oil usage for 2020 reported by the United States Energy Information Administration (~22.8 million tons) [ref 5], This survey reports paving usage by paving process (i.e., for cutback, emulsified, and a summation of heated application processes) at the Petroleum Administration for Defense Districts (PADD) and sub-PADD level. PADDs are geographic aggregations of the 50 states and the District of Columbia that were generated during World War II for 31-2 ------- purposes of administering oil allocation. At the sub-PADD level, usage resolution is provided in aggregations that include up to six states. State-level 2020 data on the production of asphalt pavement for heated applications and the proportions used in warm-mix processes at reduced temperatures are available from a National Asphalt Pavement Association (NAPA) report [ref 2], The state-level heated application usage and reduced temperature (i.e., warm-mix usage) proportions are used to allocate cutback, emulsified, hot-mix, and warm-mix usage from the Asphalt Institute survey, which is at the sub-PADD and application type-level. Therefore, it is assumed that the state-level proportions of liquid asphalt used in heated applications within a sub-PADD match the state-level proportions of liquid asphalt used in cold application (i.e., cutback and emulsified) within a sub-PADD. The derivation of state-level, per-application usage is as follows: Usages a SPUSp a ^ (1) sp Where: Usages,a SPUsp,a HAS HAsp a sp Liquid asphalt usage in state s for application a, in short tons. sub-PADD usage of liquid asphalt in sub-PADD sp associated with state s for application a from the Asphalt Institute survey, in short tons. Heated application usage in state s from the NAPA survey, in short tons. Heated application usage in sub-PADD sp associated with state s from the NAPA survey, in short tons. Application types include hot-mix, warm-mix, cutback, and emulsified. sub-PADD associated with state s. sub-PADDs include the 11 districts included in the Asphalt Institute survey [ref 1], An additional transformation must be done to split the state-level, heated application usage into hot- mix and warm-mix application, respectively. Usages a = WMAS (1 — WMAS) Usages x "" ""'sIha Usages /HA if a is warm — mix application if a is hot — mix application (2) Where: Usages,a = Liquid asphalt usage in state s for application a, in short tons. Usages = Liquid asphalt usage in state s for heated application, as derived in Eqn. 1, in short tons. WMAS = Warm-mix application usage at reduced temperatures in state s from the NAPA survey, in short tons. HAs = Heated application usage in state s from the NAPA survey, in short tons. a = Application types include hot-mix and warm-mix. State-level summation across application types in Eqn. 2 yield the state-level application usage for heated application from Eqn. 1. 31-3 ------- 31.2.2 Allocation Procedure State-level asphalt usage at the county-level is estimated using county-level vehicular miles traveled on paved roads as a proxy. Therefore, it is assumed that county-level paving activity is proportional to the estimated vehicular miles traveled on paved roads within each county in a state. The U.S. EPA's Motor Vehicle Emissions Simulator (MOVES) model incorporates county-level estimates of vehicle miles traveled for various road types when estimating emissions. These road types include (1) urban interstates, freeways, and expressways, (2) urban other principal arterial, minor arterial, major collector, minor collector, and local roads, (3) rural interstates, freeways, and expressways, and (4) rural other principal arterial, minor arterial, major collector, minor collector, and local roads. The vehicle miles traveled by road type input data that will be used in the 2020 NEI MOVES simulations will be used here. In addition, the functional systems length of these road types on a per-state basis is annually provided by the U.S. Department of Transportation's Federal Highway Administration (FHWA) [ref 6], These two datasets are combined to estimate the county-level paved vehicular miles traveled by paved road type as follows: PFSL PVMTcr = VMTcr X - c,r c,r TFSL s,r (3) s,r Where: PVMTc,r = Estimated paved vehicular miles traveled in county c on road type r, in miles. VMTc,r = Estimated vehicular miles traveled from MOVES in county c on road type r, in miles. PFSLs,r = Paved functional system length in state s associated with county c on road type r from the FHWA, in miles. TFSLs,r = Total functional system length in states associated with county c on road type rfrom the FHWA, in miles. r = Road types include (1) urban interstates, freeways, and expressways, (2) urban other principal arterial, minor arterial, major collector, minor collector, and local roads, (3) rural interstates, freeways, and expressways, and (4) rural other principal arterial, minor arterial, major collector, minor collector, and local roads. County-level paved vehicular miles traveled estimates are summed across all road types and proportioned using the results for all counties within a state. These proportions, paired with the usage estimates from Equations 1-2, yield county-level asphalt usage for each process (hot-mix, warm-mix, cutback, and emulsified) as follows: YrPVMTrr / Usageca — Usagesa x //] PVMT (4) s,r Where: Usagec,a = Liquid asphalt usage in county c for application a, in short tons. Usages,a = Liquid asphalt usage in state s associated with county c for application a, in short tons (from Eqn. 1-2). PVMTCtr = Estimated paved vehicular miles traveled in county c on road type r, in miles (from Eqn. 3). PVMTs,r = Estimated paved vehicular miles traveled in state s associated with county c on road type r, in miles (from Eqn. 3). 31-4 ------- a = Application types include hot-mix, warm-mix, cutback, and emulsified. r = Road types include (1) urban interstates, freeways, and expressways, (2) urban other principal arterial, minor arterial, major collector, minor collector, and local roads, (3) rural interstates, freeways, and expressways, and (4) rural other principal arterial, minor arterial, major collector, minor collector, and local roads. 31.2.3 Emission Factors Emission factors for all paving processes (hot-mix, warm-mix, cutback, and emulsified) captures emissions that occur during application and in-use. Both application and in-use emission factors for hot-mix and warm-mix asphalt, as well as the in-use emission factors for cutback and emulsified asphalt, were retrieved from Khare et al., 2020 [ref 4], Emission factors associated with application for cutback and emulsified asphalt paving were not updated. During the hot-mix application process, the asphalt pavement (i.e., mixture of liquid asphalt and aggregate) is heated and applied at elevated temperatures (~150 °C). Emissions are highest when sustained heating is initiated and exponentially decline thereafter. Measurements indicate that the exponential function below (Eqn. 5) fits the dynamic change in emissions over a prolonged experiment (> 6 days). However, hot-mix asphalt is not heated for prolonged periods. Here, it is assumed that the application process takes 5 hours and is meant to capture the time between transport, paving, and ambient cooling. EF = 7.7 x exp~0016xt + 16 xexp~05xt ^ Where: EF = Emission factor of gas-phase organics, in mg min1 kg 1 asphalt t = Time, in hours Integrating Equation 5 over a period of 5 hours yields an emission factor of 4 g/kg asphalt, or 8.04 lb/short ton asphalt (i.e., 0.4% emissions by weight), and represents the emissions from hot-mix asphalt during the application process. The warm-mix asphalt application process generally occurs at 20 - 40 °C cooler temperatures than hot-mix asphalt application. Reducing the asphalt temperature from 140 °C to 120 °C reduced the initial pulse of emissions by ~46% (Fig. S5 of Khare et al., 2020). As such, a warm-mix application emission factor of 2 g/kg asphalt, or 4.32 lb/short ton asphalt (i.e., 0.2% emissions by weight), is adopted. Cutback and emulsified application emission factors are developed using compositional information from material safety and data sheets (MSDS) for cutback [ref 7] and emulsified [ref 8] asphalt. Assuming a volatilization fraction of 95% for all components yields an emission factor of 813.96 lb/short ton asphalt (407 g/kg asphalt) for cutback applications and 195.51 lb/short ton asphalt (98 g/kg asphalt) for emulsified applications. In-use emissions follow application and occur under ambient temperatures. Since emissions are strongly influenced by temperature, climatological variation can impact the speed in which emissions occur. Measurements associated with a sustained heating experiment at 60 °C feature an exponential decline and fit the function below (Eqn. 6). While 60 °C is above ambient conditions for all locations within the 31-5 ------- United States, measurements show that emissions flatten within a day and remain near-constant for more than 2 additional days. Here, it is assumed that emissions within 72-hours under 60 °C will occur within 1-year under ambient conditions at all locations within the United States. Integrating Equation 6 over a period of 72 hours yields an emission factor of 1 g/kg asphalt, or 2.01 lb/short ton asphalt (i.e., 0.1% emissions by weight), and represents the emissions from all in-use asphalt paving process. EF = 0.1 + 3.3 x exp-°35xt (l Where: EF = Emission factor of gas-phase organics, in mg min1 kg 1 asphalt t = Time, in hours Taken together, the VOC emission factors for all asphalt paving process are the summation of emissions associated with application and in-use. Emissions factors are provided in the "Wagon Wheel Emission Factor Compendium" on the 2020 NEI Supporting Data and Summaries site. 31.2.4 Controls There are no controls assumed for this category. 31.2.5 Emissions Emissions are quantified using county-level liquid asphalt usage, per application, and the emissions factors provided above as follows: Where: 77 USCLQ6c,a ^ EFa I tc,a ~ /2000 (7) Ec,a = Annual emissions in county c for application a, in short tons Usagec,a = Liquid asphalt usage in county c for application a, in short tons EFa = Emission factor for application a, in lb/ton asphalt a = Application types include hot-mix, warm-mix, cutback, and emulsified 31.2.6 Sample Calculations The table below includes sample calculations for VOC emissions from emulsified asphalt (SCC: 2461022000). The values in these equations are demonstrating program logic and are not representative of any specific NEI year or county. Table 31-2: Sample calculations for emulsified asphalt usage Eq. # Equation Values Result 1 Usages a = SPUsrA x HA'/HAip 172 x 6.5^^ ^ 56 short tons of liquid asphalt usage for emulsified applications. 31-6 ------- Eq. # Equation Values Result 2 n/a; only applicable for hot- and warm-mix asphalt - - 3 PVMTcr PFSLs r = VMTcr X c'r TFSLsr 27845 1767595240 X 29637 1.66E+9 vehicular miles traveled on paved urban other roads. 3 - Repeat Eqn. 3 for other road types. 2.38E+9 vehicular miles traveled on paved roads. 4 Usageca = Usagesa x YjrPVMTcr / /lrPVMTS:r 56 short tons v 2.38E9 VMT/ x /5.16E10 VMT 2.58 short tons of liquid asphalt usage for emulsified applications 5 Ec,ci Usageca x EFa / '2000 2.58 short tons x 197.52/ / 2000 0.26 short tons of VOC emissions from emulsified asphalt 31.2.7 Improvements/Changes in the 2020 NEI Methodological updates for the 2020 NEI include methodological updates, as well as changes to activity data and emission factors. Methodological updates include emission estimates from heated paving applications (i.e., hot-mix and warm-mix asphalt application). Updated activity data for previously considered processes (i.e., cutback and emulsified asphalt application) and activity data for new processes are both generated from usage data reported by the Asphalt Institute [ref 1] and allocated by process and state using data from the National Asphalt Pavement Association [ref 2], Further allocation to the county-level is performed using estimates of vehicle miles traveled on paved surfaces, which is generated using data from the U.S. EPA's MOVES model and data from the Federal Highway Administration [ref 6], Emission factors for each asphalt process now span both application and post- application time periods [ref 4], 31.2.8 Puerto Rico and U.S. Virgin Islands Insufficient data exists to calculate emissions for the counties in Puerto Rico and the US Virgin Islands. As such, emissions are based on two proxy counties in Florida: 12011 (Broward County) for Puerto Rico and 12087 (Monroe County) for the U.S. Virgin Islands. Per-capita emission factors from Broward County and Monroe County are applied to Puerto Rico and the U.S. Virgin Islands, respectively. 31.3 References 1. 2020 Asphalt Usage Survey for the United States and Canada. The Asphalt Institute, Lexington, KY. 2. Williams, B.A., J.R. Willis, & Shacat, J. (2021). Annual Asphalt Pavement Industry Survey on Recycled Materials and Warm-Mix Asphalt Usage: 2020, 11th Annual Survey (IS 138). National Asphalt Pavement Association, Greenbelt, Maryland. doi:10.13140/RG.2.2.14846.46409. 3. U.S. Department of Transportation, Federal Highway Administration, Center for Accelerating Innovation. Warm Mix Asphalt FAQs. 4. Khare, P., Machesky, J., Soto, R., He, M., Presto, A.A., Gentner, D.R., Asphalt-related emissions 31-7 ------- are a major missing nontraditional source of secondary organic aerosol precursors. Science Advances, 6, 35, doi:10.1126/sciadv.abb9785. 5. U.S. Energy Information Administration, Petroleum & Other Liquids, Product Supplied: https://www.eia.gov/dnav/pet/PET CONS PSUP A EPPA VPP MBBL M.htm. 6. U.S. Department of Transportation, Federal Highway Administration, Functional System Length, Table HM-51 - Highways Statistics 2020. 7. Cutback Asphalt MSDS Product Supplier MSDS/SDS ID Valero 2013V04 Asphalt Emulsion Industries CUT-S DS-1 Martin Asphalt Company Jan 2007 Mohawk Asphalt Emulsions UN1999 Asphalt & Fuel Supply 211 Valero 211 Valero 210 Pollutant Avg. % by Weight Emission Factor [lb/ton]* Naphtha 40 760 Naphthalene & pah*** 0.58 11.02 Toluene*** 0.59 11.21 Xylene*** 0.99 18.81 Benzene*** 0.19 3.61 Ethylbenzene*** 0.49 9.31 Hydrogen Sulfide*** 0.09 1.71 Total VOC** - 813.96 *Assumes 95% volatilization **Excludes hydrogen sulfide (not organic) ***ls a Hazardous Air Pollutant 8. Emulsified Asphalt MSDS Product Supplier MSDS/SDS ID Marathon 0137MAR019 Marathon 0138MAR019 Asphalt Emulsion Industries EMU-SDS-1 U.S. Oil & Refining Co. 951 Pollutant Avg. % by Weight Emission Factor [lb/ton]* Naphtha 10 190 Naphthalene & PAH*** 0.29 5.51 Hydrogen Sulfide*** 0.09 1.71 Total VOC** -- 195.51 * Assumes 95% volatilization **Excludes hydrogen sulfide (not organic) ***ls a Hazardous Air Pollutant 31-8 ------- United States Office of Air Quality Planning and Standards Publication No. EPA-454/R-23-001ee Environmental Protection Air Quality Assessment Division March 2023 Agency Research Triangle Park, NC ------- |