Optimization of phytoncide emission concentration and safety evaluation for indoor applications

This study developed an oil-in-water (O/W) emulsion system for controlling the release of natural volatile organic compounds (phytoncides) and improve indoor air quality. The physicochemical properties of the emulsions were examined using Fourier-transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS). FTIR analysis showed that the characteristic peaks of the oil phase were diminished after emulsification, confirming the formation of a water-dominated structure. DLS measurements indicated that a surfactant-to-oil ratio (SOR) of 2.0 provided the most favorable conditions, producing smaller particle sizes and a lower polydispersity index (PDI) than other formulations. The diffusion behavior of total volatile organic compounds (TVOC) was evaluated in a 9.24 m³ laboratory chamber to investigate the effect of oil concentration. The 0.5% formulation maintained a stable emission profile, and the concentration converted to a typical residential volume (187 m³) remained within domestic and international guideline levels. In contrast, the 1.0% and 3.0% formulations exhibited higher initial peaks and greater variability. Quantitative analysis of major regulatory VOCs (benzene, toluene, ethylbenzene, xylene isomers, and styrene) confirmed that all compounds were detected at levels below their respective reference standards, and styrene was not detected. These results provide fundamental data on the emission characteristics and indoor air implications of phytoncide-based diffusion systems and establish a basis for future formulation optimization and full-scale application studies.