The Effect of Latitude on Carbon, Nitrogen and Oxygen Stable Isotope Ratios in Foliage and in Nitric- oxide ions of Aerosols

Cosmic rays in the upper troposphere (9000 meters to 15000 meters) initiate the following nuclear chemical reaction: 1n + 14N = > 14C + 1H. Previous research has shown a strong effect of latitude on the abundance of neutrons from cosmic rays. However, to date, there has been little exploration of the relationship between the latitude effect for cosmic-ray neutrons and latitudinal variations of stable isotope ratios in aerosols and foliage. In this study, aerosol samples (PM 4.5) and foliage samples were collected in Singapore in November 2009, February and July 2010 and in Fairbanks, Alaska, U.S.A. in January, April and September 2010. The average value of delta 15/14N in foliage in Fairbanks was -1.84 [per mil], whereas the average value in Singapore was -1.3 [per mil]. These results show a clear latitude effect on delta 15/14N in foliage. Furthermore, the average value of delta 15/14N in the nitric-oxide substances in the aerosol samples in Fairbanks was -2.70 [per mil], whereas the average value in Singapore was +7.61 [per mil], demonstrating that delta 15/14N in nitric-oxide substances from aerosol samples also experiences a latitude effect. In both Singapore and Fairbanks, it was observed that values of delta 15/14N in nitric-oxide substances from aerosols were correlated with declination. The value of delta 15/14N in nitric-oxide substances from aerosols in Fairbanks increased with increasing declination due to more active conversions from 14N to 14C by neutron bombardment.