Hydroxy fatty acids in snow pit samples from Mount Tateyama in central Japan: Implications for atmospheric transport of microorganisms and plant waxes associated with Asian dust

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.

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

10.5194/acp-2016-623 ◽

2016 ◽

Author(s):

Tomoki Mochizuki ◽

Kimitaka Kawamura ◽

Kazuma Aoki ◽

Nobuo Sugimoto

Keyword(s):

Organic Acids ◽

Long Range ◽

Atmospheric Transport ◽

Asian Dust ◽

Long Range Transport ◽

Central Japan ◽

Monocarboxylic Acids ◽

Range Transport ◽

Snow Samples ◽

Acetic Acids

Abstract. To understand the long-range transport of monocarboxylic acids from the Asian Continent to 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 as 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 (r2 = 0.73) 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 2011. Formic plus acetic acids also showed a positive correlation (r2 = 0.81) 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 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 (r2=0.76) between formic plus acetic acids and pH of melt snow samples. Our study demonstrates that Asian alkaline dusts can uptake volatile monocarboxylic acids during long-range transport and the dusts coated with organic acids may act as effective ice nuclei to cause a heavy snowfall.

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