Comparisons of GC-Measured Carboxylic Acids and AMS m/z 44 Signals: Contributions of Organic Acids to m/z 44 Signals in Remote Aerosols from Okinawa Island

An intercomparison study was conducted to evaluate the contributions of carboxylic acids to m/z 44 (COO+) signals obtained by an on-line aerosol mass spectrometer (AMS) during a field campaign at Cape Hedo, Okinawa, in the western North Pacific Rim. We report for the first time that carboxylic acids (diacids, oxoacids, benzoic acid, and fatty acids) significantly contribute to m/z 44 signals with a strong correlation (R = 0.93); oxalic acid accounts for 16 ± 3% of the m/z 44 signals and 3.7 ± 0.9% of organic mass measured by AMS. We also found that about half of AMS m/z 44 signals can be explained by diacids and related compounds, suggesting that the remaining signals may be derived from other organic acids including monocarboxylic acids (e.g., formate and acetate) in aerosol phase. This study confirms that AMS-derived m/z 44 can be used as a surrogate tracer of carboxylic acids, although the signals cannot specify the types of carboxylic acids and their molecular compositions.