ARB Research Seminar

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Characterizing MAC Refrigerant Emissions from Heavy-Duty on and Offroad Vehicles in California

Rick Baker and Andrew Burnette, Mobile Sources, Eastern Research Group, Austin, Texas

January 06, 2011
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


In a first of its kind study, data regarding heavy-duty vehicle mobile air conditioning (MAC) system refrigerant (R134a) leak rates were collected by directly measuring leak rates from in-use medium- and heavy-duty on- and off-road equipment, and by analyzing large transit bus refrigerant use records provided by fleet managers. The estimated average annual leak rates for all types of MAC systems and vehicles (except large buses) may be higher for older vehicles (2005 and older model years) Average annual leak rates for all model years combined are estimated at 257 g/yr (0.567 lb/yr). These values represent leaks resulting from typical in-use operation, and do not include emissions from equipment servicing, technician error, sudden discharge events (e.g., as a result of accidents), or other sources. The distribution of the measured leak rates cannot be firmly established, but it appears to resemble a log-normal distribution, with most results being grouped at the low-end and a few "gross emitters" with emission rates several times higher than average. These gross emitters have a disproportionate effect on the overall emission inventory. The annual R134a leak rate from large buses was estimated to be nearly 1,340 g/year (2.9 lb/year) per bus. Unlike the estimates for other vehicle types, this estimate includes all types of emissions from the MAC system.

Leak rates were combined with the off-road and medium/heavy-duty on-road vehicle population data for California to estimate annual R134a emissions. Estimated annual leakage of R134a from heavy-duty vehicles in California is estimated to be 1.35 MMT CO2E per year, assuming different leak rates by age group. Due to small sample sizes and simple assumptions for projecting leak rates to an "annualized" basis, substantial uncertainty remains regarding emission inventory estimates for this population. Results from this study may be combined with future interview and survey results from large fleet maintenance personnel to address the most significant sources of uncertainty and knowledge gaps.

Speaker Biography

Rick Baker is a senior project manager with Eastern Research Group's (ERG) Mobile Sources Group in Austin, Texas. Mr. Baker works closely with the US Environmental Protection Agency (US EPA) as well as state and local agencies in Texas, California and other areas, assisting with the development of State Implementation Plans (SIPs), US EPA reporting requirements (e.g., National Emission Inventory and National Toxics Inventory submittals), among others. Mr. Baker specializes in surveying and evaluating emissions for "hard-to-quantify" sources such as construction, commercial, and industrial non-road equipment.

Andrew Burnette is a mechanical engineer and the owner of infoWedge, an emissions measurement service provider that focuses on engine exhaust emissions, both in the laboratory and out in actual use. Over a 20-year career, primarily in the study of pollution from mobile sources, Mr. Burnette has participated in research projects in the United States, Canada, Mexico, Spain and Thailand. Frequently his work has helped adapt innovative measurement strategies to the development of pollution control policy. For example, he was the lead engineer on a project to investigate the feasibility of adding vehicle remote sensing devices (RSD) to California's mobile source emission reduction strategies and he lead the in-field implementation of an EPA project to use portable emissions measurement systems (PEMS) to record in-use emissions from over 500 vehicles in the Kansas City area. During 2010 he led the development of the emission control system for the winning vehicle in the $5M category of the Progressive Insurance Automotive X-Prize competition. His work has resulted in the co-authorship of two patents, five peer-reviewed journal articles, and over 20 presentations at industry meetings hosted by the Coordinating Research Council, the Air and Waste Management Association, the Society of Automotive Engineers, and other organizations. Mr. Burnette earned a Bachelor of Science degree in mechanical engineering from the University of Texas at Austin in 1988.

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