Estimating Emissions from Sources of Air Pollution

6.3 Estimating Emissions from Off-Road Mobile Sources

6.3.10 General Considerations Introduction

There are a number of considerations that need to be given to each class of off-road equipment that is considered. These are discussed in the following paragraphs relative to each source category. Construction Equipment

The number of pieces of construction equipment that exists at a site can vary from a single piece of equipment to many pieces of equipment. The emissions associated with each piece of equipment can be calculated as described in the previous sub-sections and allocated to a specific part of a region to establish emissions by sector of the city. The other approach is to estimate the distribution of each type of construction equipment used in a region and to calculate the overall emissions. This overall emissions can be used as a total or allocated back to the region based on measured or estimated construction activity in the various parts of the region or some other allocation modifier. The unique situation relative to construction equipment is that it is often moved from location to location in a region and may only be at a single location for a week or less. Of course, it can exist at a location for a year or more. In some cases, equipment maintained at a location for more than a year is treated as a stationary source even though for emission calculation purposes it is off-road equipment. In general it is best to determine the overall emissions from construction equipment and to allocate it to various subsections of the region of interest. Rail-Yards

Rail-Yards are confined to a few locations. Except in the case of very large urban areas there are seldom more than two to five rail-yards in a region. These rail-yards can contain a variety of off-road equipment and can include heating and cooling equipment and trucks and passenger vehicles. Since the number of rail-yards in a region are typically very limited, it is more useful if the equipment type and use by rail-yard is determined and emissions are established by rail-yard. This supports better air quality modeling as well as the determination of control cost and other regulatory considerations. The emissions from all sources that are confined to the rail-yard should be treated as part of the rail-yard emissions for air quality and policy analysis purposes. Shipping Ports

Shipping ports, like rail-yards, are confined to a few locations. A region will seldom have more than one to three shipping ports. A shipping port can contain a variety of emission sources including ships, tugboats, off-loading equipment, trains, heating and cooling equipment, packaging equipment, and trucks. The heating and cooling equipment, packaging equipment, and trucks are often treated as stationary and on-road mobile sources respectively, but it is possible to have trucks that never leave the port area. In this case, the equipment that is confined to the shipping port should be calculated as part of the shipping port emissions for modeling and generally for regulatory purposes. It is possible that the laws that exist in a location might result in emissions from different types of sources being treated independently from the port, but this is not the recommended approach. Types of equipment can be tracked by providing links in the database to equipment type categories. Airports

Airports are also confined to a few locations. A region can have from one to more than ten active airports as Los Angeles does. These airports will use a wide range of off-road equipment used to tow airplanes, to refuel airplanes, to deice airplane wings, to load and unload passengers, and to load and unload baggage. The airport may also contain heating equipment and cooling equipment. Emissions from off-road equipment used at an airport should be calculated and treated as airport emissions. Activity information on the various types of equipment at the airport will have to be determined and emission estimates made. This information will normally be combined with other airport emissions (heating and cooling) to establish total emissions by airport. This information along with airplane takeoffs can be used to establish the air quality impacts of the airports in the region and to better understand the environmental impacts compared to economic impacts.