Experiments were conducted on a laminar premixed ethylene-air flame at equivalence ratios of 2.34 and 2.64. An addition of 5% NO2 by volume was added to the flame as part of the fuel and was observed to significantly reduce (15-30%) the soot volume fraction. Soot properties were measured using light extinction, scattering and fluorescence. The flame temperatures were measured using a spectral line reversal technique in the non-sooting region, while two-color pyrometry was used in the sooting region. Chemical kinetics modeling using the PREMIX 1-D laminar flame code was used to understand the chemical role of the NO2 gas in the soot formation process. The modeling used kinetic mechanisms available in the literature. Experimental results indicated a delay in the onset of soot in the flame with NO2 added with an overall reduction in the soot volume fraction. In addition, fluorescence signals - often argued to be an indicator of polycyclic aromatic hydrocarbons (PAH) - were weaker near the burner surface for the flame with NO2 added as compared to the baseline flame. A chemical kinetics model, which included reactions for the formation of PAH species, was used to simulate these ethylene-air flames. The reduction in soot volume fraction is attributed to a decrease in the H-atom concentration due to reaction with NO2 and a subsequent reduction in acetylene in the pre-soot inception region.