Online detection of halogen atoms in atmospheric VOCs by the LIBS-SPAMS technique

Volatile organic compounds (VOCs) are one of the major pollutants in the atmospheric and indoor environment. The direct detection of halogen atoms in VOCs via laser induced breakdown spectroscopy (LIBS) is highly challenging work because of the high ionization energy of these halogen elements. In this paper, the LIBS system combined with a self-designed single particle aerosol mass spectrometry (SPAMS) system were applied to the direct online detection of VOCs in the atmosphere. The experimental parameters of LIBS experiment were optimized in the measurement of ambient air. Under the best experimental conditions, the characteristic peaks of nitrogen, hydrogen, oxygen, as well as argon, were observed in the LIBS spectra of air. Then, LIBS and SPAMS measurements were performed on Halon 2402, Freon R11 and iodomethane samples under the atmospheric pressure. The characteristic spectral lines of fluorine, chlorine, bromine and iodine were observed and recorded in LIBS spectra. The SPAMS measurements also provide the elemental compositional information of individual VOCs aerosol particles in real time, which is an effective supplement to LIBS analysis. In addition, the different isotopes of bromine and chlorine can be clearly distinguished at the same time. Finally, the home-built portable Raman spectrometer was utilized to analyze the vibrational modes and get the "spectral fingerprint" of VOCs. All the results indicate that the direct online detection performed by the LIBS and SPAMS techniques could provide elemental and isotopic information of halogen atoms in atmospheric VOCs.