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

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

Kawashima, Hiroto / Kurahashi, Takahiro

Abstract

Abstract 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 (δ ¹⁵N) of NH4 ⁺ and NO3 ⁻. The results showed an average SPM concentration of 15.6μgm⁻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 SO4 ²⁻, NO3 ⁻, Cl⁻. The annual correlation coefficient of ions indicates a very high value with NH4 ⁺ and SO4 ²⁻ (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 δ ¹⁵N–NH4 ⁺ and δ ¹⁵N–NO3 ⁻ were 16.1‰ and −0.69‰, respectively. δ ¹⁵N–NH4 ⁺ increased slightly in summer, and δ ¹⁵N–NO3 ⁻ increased considerably in winter. The trends indicated conversely. The heavy δ ¹⁵N–NH4 ⁺ 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 δ ¹⁵N–NO3 ⁻ in winter could be NOx emitted from fossil fuel combustion at low temperature. Moreover, the average δ ¹⁵N–NO3 ⁻ seemed to be made to baseline (approximately 0%) by vehicle emissions at high temperature. These results are considered to be very reasonable.

Highlights ► We investigated ammonium and nitrate source in aerosol to use nitrogen isotope. ► Stable nitrogen isotope ratio of ammonium and nitrate for long range were analyzed. ► Nitrate in winter seemed to be affected a long-range effect of coal combustion.