ARB Research Seminar

This page updated June 19, 2013

Heavy-Duty Truck Evaporative Emissions Testing for Emissions Inventory

Dennis McClement, Program Manager, Automotive Testing Laboratories, Inc., Mesa, Arizona

August 07, 2002
9500 Telstar Avenue, Annex II, El Monte, California

Research Project


One of the Air Resources Board's (ARB) more important responsibilities is to recommend the specific methods to be used to achieve ambient air quality standards. Data regarding most air pollution sources have been consolidated by the ARB into emissions inventories and models. These models are used to estimate the changes in ambient pollution levels that could be expected to result from changes in inputs to the environment. One of the largest sources of emissions is mobile sources, including motorcycles, cars, and trucks. EMFAC 2001 is the current version of the model used by the ARB to estimate emissions from mobile sources.

Historically, heavier gasoline-powered trucks were not considered major contributors to the overall evaporative emission inventory. Diesel powered vehicles do not contribute significantly to the evaporative emission inventory because of the properties of diesel fuel. The remaining gasoline-powered heavy-duty vehicles were a very small fraction of the remaining fleet. With time, however, very significant improvements have been made to the evaporative emission performance of the light-duty fleet. In addition, the sales penetration of trucks, vans, and SUV's has significantly increased, including those samples that cross the 8,500-pound boundary between light and heavy-duty emission control requirements. As a consequence, the contribution of the heavy-duty fleet has become significantly more important in relation to overall evaporative emissions.

The certification testing protocols used to control evaporative emissions have undergone major changes. These changes were implemented primarily to improve the stringency of the evaporative emission control system. As an added benefit, results of the tests using the new protocols provide a substantially improved measurement of actual in-use evaporative emission performance. This has provided the opportunity to correspondingly improve the emission factors models.

Little data exists regarding the in-use evaporative emissions performance of larger gasoline-powered trucks using the new testing protocols. The purpose of this project was to procure a small sample of in-use vehicles and to perform testing on the vehicles using the new test procedures. Nine vehicles were procured and tested. Baseline tests were performed on each vehicle. Four additional tests were performed to evaluate repeatability, the effect of temperature, and the effect of repairs performed on the vehicles. Running Loss evaporative emissions were measured while test vehicles were operated on a dynamometer in a sealed enclosure. Hot Soak tests followed the Running Loss test. A twenty-four hour variable temperature diurnal test followed the Hot Soak test.

Results were consistent with results of similar light-duty vehicles. Age, and the resulting emission control device failures, had the greatest impact on results. Older technologies, even when well maintained, do not control evaporative emissions as well as newer technologies. Larger fuel tanks tend to result in higher evaporative emission levels than smaller capacity tanks. Higher temperatures result in higher evaporative emissions.

The results of this program are available to EMFAC 2001 modelers to confirm or improve factors being used for the heavy-duty gasoline-powered class of vehicles.

Speaker Biography

Dennis McClement has served as Program Manager in a number of EPA Level of Effort Technical Directive and Work Assignment contracts. He joined ATL in 1976 as a Laboratory Technician. In this capacity he gained hands-on experience in every phase of laboratory operations. He performed vehicle preparation for testing, dynamometer driving, SHED and canister evaporative testing, and instrument operation. He performed daily, weekly, and monthly instrument calibrations and verifications. He reduced raw data to finished form, and performed quality checks on test documentation. He was assigned responsibility for training of new employees. He dealt with on-site clients from introduction to laboratory capabilities, equipment set-up to meet specific testing needs, coordination of the actual testing, and presentation and interpretation of results.

In 1978, Mr. McClement was assigned responsibility to set up and manage ATL's then newest facility in East Liberty, Ohio. The equipment was initially set up in a warehouse type area to service immediate client needs while a new building was completed. The equipment was then transferred to the new building, where Mr. McClement oversaw the installation of a second and third test cell, and a SHED enclosure.

In 1981, Mr. McClement was assigned Engineering and Project Management responsibilities. He began to write proposals for EPA, ARB, API, and CRC programs, and to serve as Program Manager when ATL was awarded the work.

Dennis transferred to a new ATL facility in New Carlisle, Indiana in 1988. He oversaw the installation of laboratory grade CVS equipment in an I/M lane in Hammond, Indiana and managed testing of more than 10,000 vehicles in that lane. In 1991, he assisted in the set up and installation of a laboratory and lane operation in Mesa, Arizona.

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