Distributions of flame temperature in silica generating coflow diffusion flames have been measured using coherent anti-Stokes Raman spectroscopy (CARS) and qualitative measurements of OH radical concentrations have been made utilizing planar laser-induced fluorescence (PLIF). Silica particles have been visualized through the plane images of light scattering from particles. The results show that aerosol generation due to chemical reactions can significantly affect thermal and chemical characteristics of hydrogen-oxygen diffusion flames. When SiCl4 is added to a flame, the temperature in non-reacting zone decreases due to the increases in both specific heat and density of the gas mixture while the flame temperature increases in the particle formation zone due to exothermal chemical reactions of hydrolysis and oxidation of SiCl4. It has also been Found that OH concentration decreases dramatically in the particle formation zone, which can be attributed to both the generation of HCl and the consumption of O-2 and H2O during silica formation.