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

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 (C-1-C-10), branched chain (iC(4)-iC(6)), 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 (iC(5))(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 atmo-spheric 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.