Sooting tendencies were measured using a yieldbased approach we developed previously . The procedure used in this study is described in . It consisted of three steps: (1) 1000 ppm of MDC, 1MN, and each mixture (mix) were separately doped into the fuel of a methane/air flame; (2) the maximum soot concentration was measured in each flame with lineof-sight spectral radiance (LSSR); and (3) these concentrations were rescaled into a yield sooting index (YSI) defined by: