Estimating Emissions from Sources of Air Pollution

6.3 Estimating Emissions from Off-Road Mobile Sources

6.3.6 Determining Activity: Population and Use of Different Sources
There are different techniques to estimate the population and use of various types of off-road sources. For the simplest approach, only the amount of fuel used in a particular activity is needed. This is described in the simple approach in an earlier section. However, for more accurate emissions analysis, more detailed information on the population and use of the off-road sources are needed, including:

* The population by engine size and type

* The hours of use by season or hour

Typical methods use engine manufacturer sales surveys, data from specific industry groups (such as the motorcycle industry council, or the consumer products safety commission), experimentally determined engine life, and surveys of equipment owners. Many times, activity is also estimated using surrogate data, and many times several methodologies are combined. For example, the population of snowblowers may be approximated originally by the sales data, and distributed regionally by tracking the snowfall data. Then, surveys may be sent out to residents asking how often they use their snowblowers.

For some categories, such as locomotives, aircraft, and commercial marine equipment, very detailed and specific information on the population and time and amount of the activity is available. For other categories, such as lawnmowers, a surrogate or survey approach is needed, and there is larger uncertainty in the overall values. Some common data sources for developing population and activity data for different sources are listed in table 6.3.6-1. One of the largest sources of US activity is the 1996 edition of the Power Systems Research (PSR) database.
6.3.6-1 Possible Sources of Population and Activity Data

Another means of collecting information that is being done in California is to require the public and commercial sectors to report and register their equipment with the air board. This is done in California. This can give an accurate method of accounting for the number of equipment, their use and allow for the ability to have the database updated on a regular basis through re-registration at a regular interval. Care must be taken to ensure that the reporting is complete and accurate, either by random sampling, incentives to correctly comply, or penalties for inaccurate reporting, or a combination of these techniques. The reporting methods used in California is considered to be adequately accurate for inventory development. It consists of a notification period, forms and instructions on reporting, and classes and online databases for reference.

Once the activity data is collected, seasonal and daily use factors should be applied to the database, based on weather data or other appropriate factors. Some of the use factors should be obvious, for example railroad and airport activities are consistent throughout the year, where as snowmobile activities would be allocated only to the winter months in most areas. For lawn and garden, there will be some but not complete seasonal variation.