Molecular Characterization of Water-Soluble Humic like Substances in Smoke Particles Emitted from Combustion of Biomass Materials and Coal Using Ultrahigh-Resolution Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Water-soluble humic like substances (HULIS) in smoke particles emitted from combustion of biomass materials and coal were characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry. The formulas identified were classified into four main groups: CHO, CHON, CHOS, and CHONS. The average H/C and O/C ratios are 1.13–1.33, 1.01–1.13, 1.26–1.48, 1.09–1.24 and 0.21–0.41, 0.27–0.45, 0.41–0.46, 0.44–0.61 for the CHO, CHON, CHOS, and CHONS groups, respectively. The CHO compound was the predominant component (43%–72%) of the smoke HULIS from biomass burning (BB) and coal combustion, followed by the CHON group for BB-smoke HULIS and the S-containing groups (i.e., CHOS and CHONS) for coal-smoke HULIS. These results indicate that the primary HULIS emitted from biomass burning contain a high abundance of CHON species, which appear to be made up mainly of oxidized nitrogen functional groups such as nitro compounds and/or organonitrates. The coal-smoke HULIS contained more compounds with relatively low molecular weight and high aromaticity index (AI_mod). They were significantly enriched in S-containing compounds with high double bond equivalent (≥4), and O/S ratios suggest that they are most likely made up of aromatic organo­sulfates and nitrooxy organo­sulfates that are usually found in polluted atmospheres. These findings imply that the primary emissions from combustion of biomass and coal fuels are potential sources of water-soluble HULIS in an atmospheric matrix and that coal combustion is an especially important source of sulfate compounds.