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 Asiancontinent to the Japanese islands, we collected snowpack samples from a pitsequence (depth ca. 6 m) at the Murodo-Daira snowfield near the summit ofMt. Tateyama, central Japan, in 2009 and 2011. Snow samples ( = 16) wereanalyzed for normal (C–C), branched chain (iC–iC),aromatic (benzoic and toluic acid isomers), and hydroxyl (glycolic andlactic) monocarboxylic acids, together with inorganic ions and dissolvedorganic carbon (DOC). Acetic acid (C) was found to be a dominantspecies (average 125 ng g), followed by formic acid (C)(85.7 ng g) and isopentanoic acid (iC) (20.0 ng g).We found a strong correlation ( =  0.88) between formic plus acetic acidsand non-sea-salt Ca that is a proxy of Asian dust. Contributions oftotal monocarboxylic acids to DOC in 2009 (21.2 ± 11.6 %) were higherthan that in 2011 (3.75 ± 2.62 %), being consistent with higherintensity of Asian dust in 2009 than in 2011. Formic plus acetic acids alsoshowed a positive correlation ( =  0.90) with benzoic acid that is atracer of automobile exhaust, indicating that monocarboxylic acids and theirprecursors are largely emitted from anthropogenic sources in China and/orsecondarily produced in the atmosphere by photochemical processing. Inaddition, the ratio of formic plus acetic acids to nss–Ca (0.27) wassignificantly higher than those (0.00036–0.0018) obtained for reference dustmaterials of Chinese loess deposits from the Tengger and Gobi deserts. Thisresult suggests that volatile and semi-volatile organic acids are adsorbed onthe alkaline dust particles during long-range atmospheric transport.Entrainment of organic acids by dusts is supported by a good correlation ( = 0.87) between formic plus acetic acids and pH of melt snow samples. Ourstudy suggests that Asian alkaline dusts may be a carrier of volatilemonocarboxylic acids.