The purpose of this study was to develop and test a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) method, a fast and non-destructive method without extraction, and compare it with the standard gas chromatography (GC) method currently used. A micro-orifice uniform deposit impactor (MOUDI) was used to sample all the size distributions of the aerosol particles of essential oils to investigate the relation between size distributions and the indoor concentration distributions of ylang essential oils. Correlation coefficients for DRIFTS and GC were 0.9904, 0.9910, 0.9913, and 0.9983 for eugenol, isoeugenol, methyl ether, and eugenyl acetate, respectively. The results showed that the concentrations of the four eugenol derivatives of smoke were approximately three times higher than those of mist. Additionally, the major size distributions of aerosol were 0.19 μm and 1.8 μm for the smoke and mist methods, respectively. Because these two methods produce similar results, DRIFTS is a practical method for assessing these fragrances in aerosols.