Ultrahigh-resolution FT-ICR mass spectrometric identification of water-soluble AOM in nonurban organic aerosols

Water-soluble atmospheric organic matter (AOM) is a complex mixture of thousands of organic compounds which may have significant influence on the climate-relevant properties of atmospheric aerosols. To understand the potential influence, the water-soluble fraction of ambient aerosols was analyzed by positive and negative electrospray ionization Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Approximately 4000 negative and 1000 positive chemical formulas were identified. The formulas contained carbon, hydrogen, oxygen, nitrogen, and sulfur atoms over the mass range of 100-800 in both modes. The range of double bond equivalence (DBE) values, the average O/C and H/C ratios of the negative ions were 0-14, 0.53, and 1.48, respectively. The range of DBE values, the average O/C and H/C ratios of the positive ions were 0-17, 0.33, and 1.40, respectively. Despite the range of DBE values, the majority compounds were found in the aliphatic region of the van Krevelen diagram