Abstract
Abstract. To understand the long-range transport of monocarboxylic acids from the Asian continent to the Japanese islands, we collected snowpack samples from a pit sequence (depth ca. 6 m) at the Murodo-Daira snowfield near the summit of Mt. Tateyama, central Japan, in 2009 and 2011. Snow samples (n = 16) were analyzed for normal (C1–C10), branched chain (iC4–iC6), aromatic (benzoic and toluic acid isomers), and hydroxyl (glycolic and lactic) monocarboxylic acids, together with inorganic ions and dissolved organic carbon (DOC). Acetic acid (C2) was found to be a dominant species (average 125 ng g−1), followed by formic acid (C1) (85.7 ng g−1) and isopentanoic acid (iC5) (20.0 ng g−1). We found a strong correlation (r = 0.88) between formic plus acetic acids and non-sea-salt Ca2+ that is a proxy of Asian dust. Contributions of total monocarboxylic acids to DOC in 2009 (21.2 ± 11.6 %) were higher than that in 2011 (3.75 ± 2.62 %), being consistent with higher intensity of Asian dust in 2009 than in 2011. Formic plus acetic acids also showed a positive correlation (r = 0.90) with benzoic acid that is a tracer of automobile exhaust, indicating that monocarboxylic acids and their precursors are largely emitted from anthropogenic sources in China and/or secondarily produced in the atmosphere by photochemical processing. In addition, the ratio of formic plus acetic acids to nss–Ca2+ (0.27) was significantly higher than those (0.00036–0.0018) obtained for reference dust materials of Chinese loess deposits from the Tengger and Gobi deserts. This result suggests that volatile and semi-volatile organic acids are adsorbed on the alkaline dust particles during long-range atmospheric transport. Entrainment of organic acids by dusts is supported by a good correlation (r = 0.87) between formic plus acetic acids and pH of melt snow samples. Our study suggests that Asian alkaline dusts may be a carrier of volatile monocarboxylic acids.
Highlights
Low molecular weight (LMW) monocarboxylic acids such as formic (HCOOH) and acetic (CH3COOH) acids are present in the atmosphere as major gaseous and particulate organic components (e.g., Kawamura and Kaplan, 1984; Kawamura et al, 2000; Paulot et al, 2011)
Homologous series of low molecular weight normal aliphatic (C1–C10), branched chain, hydroxy, and aromatic monocarboxylic acids were detected in the snow pit samples (Table 2)
Low molecular weight normal (C1–C10), branched chain, hydroxyl, and aromatic monocarboxylic acids were detected in the snow pit samples collected from MurodoDaira snowfield near the summit of Mt
Summary
Low molecular weight (LMW) monocarboxylic acids such as formic (HCOOH) and acetic (CH3COOH) acids are present in the atmosphere as major gaseous and particulate organic components (e.g., Kawamura and Kaplan, 1984; Kawamura et al, 2000; Paulot et al, 2011). Gaseous and particulate formic and acetic acids have been reported in urban (Kawamura et al, 2000), forest (Andreae et al, 1988), high mountain (Preunkert et al, 2007), marine (Miyazaki et al, 2014), and Arctic samples (Legrand et al, 2004). LMW monocarboxylic acids have been detected in wet deposition such as rain, cloud and fog water, and snow samples (Maupetit and Delmas, 1994; Keene et al, 1995; Kawamura et al, 1996, 2012). It is important to note that organic acids largely contribute to total acidity of rainwaters (Kawamura et al, 1996; Keene et al, 1983)
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