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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules
3. Non-Point Sources Non-point sources are also called area sources. These sources collectively represent individual sources of emissions that have not been inventoried as specific point or mobile sources. These individual sources treated collectively as non-point sources are typically too small, numerous, or difficult to inventory using the methods for the other classes of sources.
Non-point sources that MDE
evaluated for the 2017 Baltimore BYE
include petroleum distribution losses e.g., tank truck unloading and auto refueling, stationary source solvent application e.g., dry cleaners, auto refinishing, bioprocess emissions sources bakeries, breweries, wineries, distilleries, catastrophic/accidental releases e.g., oil spills, solid waste disposal treatment, and recovery e.g., open burning, small stationary source fossil fuel use e.g., small utility boilers, fugitive sources e.g., construction activity and unpaved roads, fire sources e.g., agricultural burning and vehicle fires, and ammonia sources e.g., agricultural livestock production operations. Appendix A sets out the methodologies MDE used to estimate emissions for each of these non-point source categories. These methods are consistent with the most recent EPA
emission inventory guidance.

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4. Non-Road Mobile Sources Non-road mobile sources are also called off-highway mobile sources.
These are defined as a non-road engine or non-road vehicle. As per 40 CFR
51.50, a non-road engine is an internal combustion engine including the fuel system that is not used in an on-road motor vehicle or a vehicle used solely for competition, or that is not affected by sections 111 or 202 of the CAA. Also defined by 40 CFR 51.50, a non-road vehicle rather than engine is a vehicle that is run by a non-road engine and that is not an on-road motor vehicle or a vehicle used solely for competition.
Examples of non-road mobile sources include airport ground support equipment, agricultural and construction equipment powered by an internal combustion engine, and lawn and garden engines and equipment.
As explained in Appendix A, consistent with EPAs Emission Inventory Guidance for Implementation of Ozone and Particulate Matter NAAQS
and Regional Haze Regulations, MDE
used the most current version of EPAs NONROAD2008a model, which is incorporated into EPAs Motor Vehicle Emission Simulator MOVES model, specifically MOVES2014a, to develop
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the inventory for non-road mobile sources. The NONROAD2008a model includes more than 80 basic and 260
specific types of non-road equipment and further stratifies equipment types by horsepower rating. Fuel types include gasoline, diesel, compressed natural gas CNG, and liquefied petroleum gas LPG.
5. Marine Vessels, Airport, Railroad Locomotives MAR Sources MAR is a non-road sub-category. MDE
states in its Baltimore base year inventory SIP that, for MAR sources, MDE calculated emissions by collecting data directly from surveyed sources, or activity from state and federal reporting agencies. To develop the commercial marine vehicle emissions for the base year, Maryland used EPAs 2016 beta modeling platform. This platform was used because it provided the most recent descriptions and methodologies for calculation of marine vessel emissions. To estimate emissions for aircraft, Maryland used airport activity statistics from the Federal Aviation Administration FAA, landing and takeoff cycle information from the Maryland Aviation Administration, and statewide survey information for landing and takeoffs, engine type, location, and usage data. Railroad emission estimates were developed using activity and fuel consumption estimates collected from the rail companies and proportioned to each county by the amount of track miles each company utilized in a county.
MDE applied EPA emission factors using EPA guidance and methodologies or the best engineering method. These methods of calculating emissions are consistent with the most recent EPA
emission inventory guidance.4 Details of the development of emissions for these sources along with other non-road model sources are provided in Appendix A of Marylands July 30, 2020
submittal.
6. On-Road Mobile Sources On-road mobile sources are also called highway mobile sources. These sources are the motor vehicles e.g., automobiles, buses, trucks traveling on local and highway roads. On-road mobile sources should be estimated by the latest recommended on-road mobile source models. Currently, that means 4 Emission Inventory Guidance for Implementation of Ozone and Particulate Matter National Ambient Air Quality Standards NAAQS
and Regional Haze Regulations, Page 130, included in the docket for this rulemaking available online at https www.regulations.gov, Docket ID: EPA
R03OAR20210017 PG 130.

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EPAs MOVES model for all states but California.
In addition to emissions from vehicles exhaust, the MOVES model estimates evaporative emissions for mobile sources, which must be included in the inventory. Volatile hydrocarbons evaporate from the fuel system while a vehicle is refueling, parked, or driving.
Evaporative processes differ from exhaust emissions because they dont directly involve combustion, which is the main process driving exhaust emissions.
As stated in Appendix A, MDE used EPAs MOVES2014a model to estimate the 2017 annual emissions as well as 2017 daily emissions from on-road vehicles and total energy consumption in Maryland. Emissions were estimated based on emission factors and vehicle activity. Emission factors for vehicles were based on vehicle type such as passenger cars, passenger trucks, vehicle age and the vehicles operating modes.
Operating modes for running, start, and idle emissions are included in MOVES.
The emission factors varied over a range of conditions, such as the ambient air temperature, speed, traffic conditions, road types, road topography, etc. The generated emission factors were then multiplied by the appropriate vehicle miles traveled VMT to estimate emission.
In order to estimate both the rate at which emissions are being generated and to calculate VMT, MDE examined its road network and fleet to estimate vehicle activity. For the annual inventories, this was done for each of the twelve months in 2017 and aggregated for the entire year. MDE used computer models to perform these calculations by simulating the travel of vehicles on the Marylands roadway system.
EPA has reviewed the results, procedures, and methodologies for the SIP base year, as well as comparing the inventory with previously QA/QCd data in EPAs 2017 NEI for any data discrepancies and found none. EPA has therefore determined the base year inventory to be acceptable and developed in accordance with EPAs technical guidance.
7. Biogenic Emissions MDE also inventoried biogenic emissions, which are not included in the anthropogenic total. Biogenic emissions come from natural sources, including vegetation, soils, volcanic emissions, lightning, and sea salt. They need to be accounted for in photochemical grid models, as most types are widespread and ubiquitous contributors to background formation of
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