This Executive Summary provides an overview and introduction to the Coordinating Research Council E-37 Research Program, "The Effect of Air Conditioning on Regulated Emissions from In-Use Vehicles." This program was sponsored by the Coordinating Research Council (CRC), the California Air Resources Board (ARB), and the Texas Commission on Environmental Quality to evaluate the effects of air conditioning (AC) operation on vehicle emissions and fuel economy. The detailed results from this program are presented in two laboratory test reports with associated data files and in 27 separate statistical analysis reports. A technical paper prepared for the Society of Automotive Engineers (SAE) 1 describes the full program and presents detailed results and conclusions of the statistical analyses. The technical paper is available for purchase from SAE. The laboratory reports and associated data files as well as the statistical analyses are available from the CRC. SUMMARY OF RESULTS The program results demonstrated that AC operation had a substantial impact on emissions and fuel consumption. Operation of the vehicle AC system over a range of environmental conditions resulted in consistent increases in vehicle emissions of nitrogen oxides (NO x) and carbon monoxide (CO). NO x increased by 0.1 to 0.6 g/mile, depending on the severity of the test cycle and ambient conditions. CO increased by 0.5 to 12 g/mile. Hydrocarbon emissions were not affected by air conditioning use except in a few, limited cases. The application of solar load to the vehicle increased the impact of AC operation. The application of solar load increased NO x emissions by 0.10 to 0.14 g/mile. Although this experiment was not designed to specifically address fuel economy, operation of the vehicle AC system caused substantial decreases in vehicle fuel economy, ranging from 2.5 to 4.5 miles/gallon. The addition of solar load increased the effect on fuel economy, primarily at less severe ambient conditions. Solar load caused a decrease of 1.3 miles/gallon at 80°F and moderate humidity. The results of the program were intended to aid in the improvement of vehicle emissions inventory models. NO x emission increases due to the use of AC ranged from 15% to 100% of baseline levels. CO increases due to the use of AC varied considerably depending on the test cycle and ambient conditions. The percentage increase in CO emissions from baseline levels ranged from 0% (no statistical effect) to as high as 200%. These effects indicate that AC use can have a significant effect on vehicle emissions and should be accounted for in the inventory models.
During the 1940s, an unusual form of air pollution was experienced in the Los Angeles (LA) area of Southern California. Referred to as LA smog, this pollution differed from previously known air pollution with respect to its temporal patterns (daytime formation and nighttime dissipation), eye irritation, high oxidant levels, and plant damage. Early laboratory and field experimentation discovered the photochemical origins of LA smog. Though mechanistic understanding was incomplete, it was determined that hydrocarbon (HC) compounds in the atmosphere participate in smog formation, enabling build-up of higher ozone concentrations than would otherwise occur. It being a significant source, there was great interest in characterizing and controlling HC emissions from motor vehicles. Considerable work was done in the 1940s and 1950s to understand how emissions varied with vehicle operating conditions and deterioration of engine components. During this time, procedures were developed (and improved) to sample and quantify vehicle emissions. Besides exhaust, HC emissions from crankcase blowby, carburetor evaporation, and fuel tank losses were measured and characterized. Initial versions of both catalytic and non-catalytic exhaust after-treatment systems were developed. The knowledge gained from this pre-1960 work laid the foundation for many advancements that reduced vehicle emissions and improved air quality during subsequent decades.
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