Inorganic ion and nitrogen isotopic compositions of atmospheric aerosols at Yurihonjo, Japan: Implications for nitrogen sources

We studied the suspended particulate matter (SPM) collected in Akita Prefecture, Japan from April 2008 to January 2009 for inorganic ion composition and nitrogen isotopic ratio (delta N-15) of NH4+ and NO3-. The results showed an average SPM concentration of 15.6 mu g m(-3). The seasonal trend for SPM was higher values in the spring, lower in the winter. The major cations were Na+, NH4+, Ca2+ and major anions were SO42-, NO3-, Cl-. The annual correlation coefficient of ions indicates a very high value with NH4+ and SO42- (R = 0.93), NO3- and K+ (R = 0.65), NO3- and Ca2+ (R = 0.62). The high springtime values are the apparent result of the dust stream from Asia. Average delta N-15-NH4+ and delta N-15-NO3- were 16.1 parts per thousand and -0.69 parts per thousand, respectively. delta N-15-NH4+ increased slightly in summer, and delta N-15-NH4+ increased considerably in winter. The trends indicated conversely. The heavy delta N-15-NO3- in summer appears to be from agricultural sources such as animal waste and fertilizer. In addition, according to the difference in isotopes of NOx sources as the precursor of NO3-, the dominant origin of heavy delta N-15-NO3- in winter could be NOx emitted from fossil fuel combustion at low temperature. Moreover, the average delta N-15-NO3- seemed to be made to baseline (approximately 0%) by vehicle emissions at high temperature. These results are considered to be very reasonable. (C) 2011 Elsevier Ltd. All rights reserved.