This rescaling eliminates sources of systematic uncertainty such as the optical properties of the soot. Furthermore, it allows the new results to be quantitatively compared to a database that contains measured YSIs for hundreds of organic compounds . The parameters YSIT and YSIH are constants that define the YSI scale; their values-170.9 and 36.0-were taken from the database so that the newly measured YSIs would be on the same scale for a direct comparison. The dopants are added at a small concentration to eliminate indirect effects such as changes in the flame temperature or residence time. Supplemental Information (SI) A lists the sources and purities of each reactant. SI B shows a schematic diagram of the apparatus and describes the experiments in detail. SI C gives details of the burner . The liquid lactones were injected into the gas-phase CH4 fuel mixture with a syringe pump. SI D lists the liquid-phase flowrates corresponding to 1000 μmol/mol in the gas-phase for each test fuel, and the property values that were used to calculate them . The fuel lines were heated to 100 ℃, and the burner was heated to 170 ℃. Each test fuel was injected for 600 s and L was averaged from 300 to 600 s-SI E shows that the initial 300 s is adequate for all the test fuels to equilibrate with the walls of the fuel line and burner. SI F experimentally confirms that the test fuels were not condensing in the fuel delivery system. Isooctane was included in each measurement set as an internal standard-SI G shows that its measured YSIs were consistent over time and agreed with previous measurements .