Hydrogen Carbonate in precipitation derived from Asian Dust

In an attempt to identify the ionic imbalance, hydrogen carbonate, HCO3- (bicarbonate), was determined together with the commonly determined nine major ions because the imbalance was frequently encountered in the chemical analysis of samples with high pHs. Titration method was applied for the determination to the samples with pH higher than 5.6. These samples amounted to 102 of the 1, 536 samples collected in Hokkaido, Northern Japan, from April 1998 to December 2002. Of the 102 samples, 74 (Group A) showed an acceptable ion balance without including HCO3-. In the other 28 (Group B), however, inclusion of HCO3- successfully improved the ion balance. These results suggested that HCO3- was a potential candidate for explaining the imbalance. The hydrogen carbonate concentrations showed a strong correlation with the corresponding non-sea salt calcium (nss-Ca2+) concentrations, which implied that HCO3- was derived from calcium carbonate particles incorporated into falling raindrops or cloud droplets. For Group A, the relationship between HCO3- and the nss-Ca2+ concentration was very similar to that for commonly suspended particles in Hokkaido. On the other hand, Group B exhibited a stronger but significantly different correlation. To the samples of Group B, a back trajectory analysis was applied to demonstrate that the samples were associated with aerosol travelling from Northern China or Mongolia