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Air Quality Analysis Guidance Handbook

Off-road Mobile Source Emission Factors

The A9-8 tables of the 1993 Handbook provide a methodology and emission factors for calculating off-road mobile source emissions from equipment such as loaders, tractors, dozers, graders, etc.  Using this methodology requires relatively detailed knowledge of the types of equipment that may be used as part of a proposed project.  The CEQA practitioner may use the 1993 Handbook methodology to calculate off-road mobile source emissions.  Alternatively, to simplify calculating off-road mobile source emissions the CEQA practitioner may use the composite off-road emission factors from CARB's Off-Road Model.  The composite off road emission factors were derived based on the equipment category (tractor, dozer, scraper, etc.), average fleet make-up for each year through 2020, vehicle population (number) in each equipment category by horsepower rating and load factor.  Two types of composite emission factors have been developed - composite and horsepower-based composite factors.  Composite emission factors have horsepower rating and load factors already built into the emission factors, so the CEQA practitioner does not necessarily need to know these two parameters when calculating off-road mobile source emissions.  Horsepower-based composite factors have load factor ratings built into the emission factors. The CEQA practitioner can choose the appropriate equipment by horsepower rating, if this is known, to tailor the analysis of the proposed project to more accurately estimate emissions.  Daily emissions are calculated as follows.

E = n x H x EF  :where:
E = emission in pounds per day
n = number of pieces of equipment in a specified equipment category
H = hours per day of equipment operation
EF = the off-road mobile source emission factor by equipment category or horsepower-based equipment category in pounds per hour (to access the composite off-road emission factors, click on the "Off-road Mobile Source Emission Factors (Scenario Years 2006 – 2020)" hypertext link below)

Please note, the following off-road emission factors include CO2 and CH4 emission factors.