Nitrogen isotopes of ammonium (delta N-15-NH4+) in precipitation have been analyzed, to study their monthly from Oct. 2008 to Sep. 2009 at Guiyang, Southwest China. delta N-15-NH4+ values were higher in and lower in summer showing a strong sine curve. In summer (rainy season), raindrop may more light ammonia by washout process, because raindrop incorporated (NH3)-N-15 preferentially left the N-14 in the atmosphere. At the same time, longer sunshine times imply more hv for H2SO4 of SO2 to H2SO4, which accelerates gaseous to particle conversion of NH3 to (NH4)(2)SO4 unidirectional reactions for isotopic enriched N-14. The above two aspects can somewhat cause the variation of nitrogen isotopic composition, but are not the main or direct reasons. The has an opposite trend with seasonal variation of delta N-15 values. The temperature not only seasonal variation of delta N-15 values, but also increases the volatilization rate of NH3 and microbial And there is a robust linear relationship between temperature and delta N-15, showing that the is the main factor to decide the monthly variation of delta N-15-NH4+. (C) 2012 Elsevier Ltd. All rights reserved.
