“…Nevertheless, the availability of this data has led to widespread use of these laboratory results to predict real-world pollutant levels using emission factor models such as EMFAC (California Air Resources Board) and MOBILE (U.S. EPA). Recent ®eld studies of actual emissions via tunnel studies (Pierson et al, 1990;McLaren et al, 1996), roadside point sampling, across-the-road remote sensing (Lawson et al, 1990;Bishop et al, 1993;Stephens, 1994;Stedman, 1996;Woods, 1996;Zhang et al, 1996), and instrumented vehicles (Schurmann and Staab, 1990;Kelly and Groblicki, 1993;Guenther et al, 1996) have noted the inadequacies of using laboratory data to estimate real-world pollutant levels. These inadequacies are generally attributed to factors such as the limitations of the test driving cycle, vehicle tampering, poor vehicle maintenance, and the high frequency of`o -cycle' driving events under actual driving conditions (Black, 1991;Ross, 1994).…”