Water-soluble organic nitrogen in high mountain snow samples from central Japan

We measured water-soluble organic nitrogen (WSON) in snow pit samples, which were collected at the Murodo-Daira snowfield near the summit of Mt. Tateyama, central Japan in 2008, 2009, and 2011. The concentrations of WSON ranged from 12.8 to 96.7 ng g^-1, which were significantly lower than those reported in continental wet deposition samples from the Asian continent. WSON may be largely diluted in the snow samples during snowing processes over the high mountains. We found that WSON significantly correlated with nss-Ca²⁺ and water-soluble organic carbon (WSOC). Concentrations of WSON are likely controlled by the intensity of Asian dust events. Contributions of WSON to water soluble total nitrogen (WSTN) in snow pit sequence was found to be 15 ± 10%, which is lower than those (63-91%) of reference dust materials collected in China. Mass concentration ratio of WSOC/WSON was on average 23.7, which is significantly higher than the C/N weight ratio (5.6) calculated from the Redfield ratio. This result suggests that WSOC is largely produced by secondary photochemical oxidation of anthropogenic volatile organic compounds during the transport from East Asia to the high mountain areas in Japan. On the other hand, WSON may be contributed from Asian dusts from arid areas in China whereas water-soluble inorganic nitrogen may be derived from pollution sources.