INTRODUCTION The chemical species responsible for the characteristic diesel exhaust odor have been identified in the previous effort on this program(1-4) The effort during the most recent of these studles(4) was to obtain quantitative means of collecting and analyzing the odorous species in order that an Instrumental method could eventually be developed. Our research program continually emphasizes the interrelationship between the sensory measurement by experienced odor chemists and the analytical chemical measurements while developing the measurement schemes. Some details of the previous work which are especially relevant to the work reported here are included in Appendices A-C@ The basic odor measurment techniques and new dose esponse odor measurement method are described in Appendix A@ The chemical composition and odor assignments of the two major exhaust odor groups@ smoky-burnt and oily-kerosene@ are summarized in Appendix B@ Appendix C describes the details of the diesel exhaust odor collection methods used in these studies@ The details of our studies of typical diesel exhaust odors may be summarized by describing diesel exhaust as consisting of two principal groups@ oily-kerosene and smoky-burnt@ each of which contributes significantly to diesel exhaust odor. The smoky-burnt odor is normally the most Intense of the two odor groups and most characteristic of odors associated with the combustion process. A new procedure@ which calculates the exhaust odor intensity at a 1000/1 dilution from the dose esponse data@ is used in place of the earlier procedures of reporting TIA values at a single dilution. Methods for the quantitative collection of the diesel exhaust odors using Chromosorb 102 are detailed in Appendix C. The total organic extract (TOE)@ isolated from the sample traps by solvent elution@ may be resolved into three functionally distinct chemical groups using liquid chromatography (LC) methods. Species with volatility equal to or greater than pentane would not be detected by these procedures@ but they have much less odor than the higher molecular weight species. This approach separates the TOE sample into 1) an odorless paraffin fraction (LCP)@ 2) an aromatic fraction (LCA) containing the oilykerosene odor group@ and 3) an oxygenate fraction (LCO) containing the smoky-burnt odor group. The overall relationship of these samples and fractions is shown In Figure 1@ The previous work(^) had shown that the smoky-burnt LCO exhaust fraction was the most significant odor group and indicated that it was possible to measure the total diesel exhaust odor Intensity (TIA@ see Appendix A) by measurement of the abundance of the total LCO group. The LCO measurement was made using an analytical liquid chromatography (ALC) method utilizing an ultraviolet absorption detector. The preliminary studies Indicated that the exhaust odor intensity could be measured by a relationship of the form TIA = a + b log LCO where the odor Intensity is the value computed at a diluted exhaust concentration of 1 ? exhaust/m'^ of dilution air (1 ?/m3)@ and the LCO concentration is reported in vg/i (or mg/m3 ) of exhaust. The purpose of the research described in this report was@ first@ to verify our preliminary observations of the TIA-LCO correlation by studying exhaust generated over a wide range of conditions@ and@ second@ to develop a final (automated) instrument which could be used in any diesel odor research laboratory.