Low molecular weight (C_1-C_(10)) monocarboxylic acids, dissolved organic carbon and major inorganic ions in alpine snow pit sequence from a high mountain site, central Japan

摘要

Snowpack samples were collected from a snow pit sequence (6 m in depth) at the Murodo-Daira site near the summit of Mt. Tateyama, central Japan, an outflow region of Asian dusts. The snow samples were analyzed for a homologous series of low molecular weight normal (C_1- C_(10)) and branched (iG_4-iC_6) monocarboxylic acids as well as aromatic (benzoic) and hydroxy (glycolic and lactic) acids, together with major inorganic ions and dissolved organic carbon (DOC). The molecular distributions of organic acids were characterized by a predominance of acetic (range 7.8-76.4 ng g~(-1)-snow, av. 34.8 ng g~(-1)) or formic acid (2.6-48.1 ng g~(-1), 27.7 ng g~(-1)), followed by propionic acid (0.6-5.2 ng g~(-1) 2.8 ng g~(-1)). Concentrations of normal organic acids generally decreased with an increase in carbon chain length, although nonanoic acid (C9) showed a maximum in the range of C_5-C_(10). Higher concentrations were found in the snowpack samples containing dust layer. Benzoic acid (0.18-4.1 ng g~(-1) 1.4 ng g~(-1)) showed positive correlation with nitrate (r = 0.70), sulfate (0.67), Na~+ (0.78), Ca~(2+) (0.86) and Mg~+ (0.75), suggesting that this aromatic acid is involved with anthropogenic sources and Asian dusts. Higher concentrations of Ca~(2+) and SO_4~(2+) were found in the dusty snow samples. We found a weak positive correlation (r = 0.43) between formic acid and Ca~(2+), suggesting that gaseous formic acid may react with Asian dusts in the atmosphere during long-range transport. However, acetic acid did not show any positive correlations with major inorganic ions. Hydroxyacids (0.03-5.7 ng g~(-1), 1.5 ng g~(-1)) were more abundant in the granular and dusty snow. Total monocarboxylic acids (16-130 ng g~(-1), 74 ng g~(-1)) were found to account for 1-6% of DOC (270-1500 ng g~(-1), 630 ng g~(-1)) in the snow samples.