Long-range atmospheric transport of volatile monocarboxylic acids with Asian dust over a high mountain snow site, central Japan

摘要

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 (in/i?=?16) were analyzed for normal (Csub1/sub–Csub10/sub), branched chain (iCsub4/sub–iCsub6/sub), aromatic (benzoic and toluic acid isomers), and hydroxyl (glycolic and lactic) monocarboxylic acids, together with inorganic ions and dissolved organic carbon (DOC). Acetic acid (Csub2/sub) was found to be a dominant species (average 125?ng?gsup?1/sup), followed by formic acid (Csub1/sub) (85.7?ng?gsup?1/sup) and isopentanoic acid (iCsub5/sub) (20.0?ng?gsup?1/sup). We found a strong correlation (ir/i?=??0.88) between formic plus acetic acids and non-sea-salt Casup2+/sup 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 (ir/i?=??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–Casup2+/sup (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 (ir/i?=?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.