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12 Figure III-5. Speciated VOC emissions data normalized to the N1 = 25% test result. The data for this aircraft engine is SA012 and can be found in Appendix A. Ethene (circles), formaldehyde (squares), and benzene (triangles) have been plotted and fit as a function of fuel flow. Gaussian profile, depicted in Figure III-6 as the dashed-dot ICAO databank of -544 (s kg-1) as depicted in Figure III-4. line, asserts a central value and Gaussian half width of -5117 The width of this distribution will be revisited after a sum- (s kg-1), assuming the data are described by normal distribution. mary of the error analysis associated with the emission index Whether this is a good assumption may not be known without measurements. measuring a much larger sample; however, it at least provides a metric for gauging the width of the distribution. III.4Systematic Error and The two dominant VOC compounds by mass--ethene Fuel Flow Dependence and formaldehyde--are characterized by average and standard deviation values of -6016 and -4910 (s kg-1). The measured The plume sampling methodology has a known bias of +2% VOC/fuel flow dependence compares favorably with that (see Appendix A). Typically, the precision error in any single determined for the UHC emission indices derived from the determination of an emissions index is much less than 5% Occurrences Figure III-6. Histogram of the measured dependence of VOC emission on fuel flow for all engines and speciated VOCs measured in the study. The dashed-dot line is a Gaussian fit to the distribution.