Polarity Dependent Chemical Characteristics of Water-Soluble Organic Matter from Laboratory-Generated Biomass Burning Revealed by 1-Octanol-Water Partitioning.

Abstract

Polarity distribution of water-soluble organic matter (WSOM) is an important factor in determining hygroscopic and cloud nucleation abilities of organic aerosol particles. We applied a novel framework to quantitatively classify WSOM based on 1-octanol-water partition coefficient ( KOW), which often serves as a proxy of polarity. In this study, WSOM was generated by laboratory biomass burning experiment with smoldering of Indonesian peat and vegetation samples. The fractionated WSOM was analyzed using the UV-Visible spectrophotometer, spectrofluorometer, and time-of-flight aerosol chemical speciation monitor (ToF-ACSM). Several deconvolution methods, including positive matrix factorization, parallel factor analysis, and least-squares analysis, were applied to the measured spectra, resulting in three classes of WSOM. The highly-polar fraction of WSOM, which predominantly exists in the range of log KOW < 0, is highly oxygenated and exhibits similar optical properties to those of light-absorbing humic-like substances (HULIS, termed after the humic substances due to the similarity in chemical characteristics). WSOM in the least-polar fraction, which mainly distributes in log KOW > 1, mainly consists of hydrocarbon-like and high molecular weight species. In between the highly- and least-polar fraction, WSOM in the marginally-polar fraction likely contains aromatic compounds. The analyses have also suggested the existence of HULIS with different polarities. Comparison with previous studies indicates that only WSOM in the highly-polar fraction (log KOW < 0) likely contributes to water uptake.