抄録
During the monsoon season in 2011 (July to August), 33 rainwater samples were collected at Gongabu, Kathmandu Valley, Nepal. The major ions and stable isotopic compositions of nitrogen and oxygen of NO3- were measured to identify the NO3- sources in rainwater. Temporal variation in the major ions in rainfall shows that higher concentration corresponds to low rainfall, but a high volume of rainfall also shows the same pattern, indicating an atmosphere polluted with dust. Rainwater chemistry was analyzed using correlation and principal component analysis to identify the possible sources of the measured ions. Two components were identified, which accounted for 85.5% of total variance: (1) soil and secondary particles (73.6%) that were possibly from fertilizers and incomplete combustion of fuel (K+, Cl-, NH4+, NO3-, SO42- and Mg2+); and (2) soil (11.9%) of natural origin (Ca2+ and HCO3-). The concentration of NH4+ was generally high when compared to NO3-. However, NO3- concentration was high in some rainfall events, making it difficult to identify the origin as either agricultural or industrial activities. The δ15N value was within the range -5.9‰ to +3.3‰ for NO3-. Moreover, a relatively low and unique value of δ18O of NO3- (+12.2‰ to +44.5 ‰) was found, compared with most values reported from around the world (› +60 ‰). This suggests the deposition of soil containing nitrate fertilizers and its mixture of atmospheric nitrate that had low δ18O values.
