SULFUR ISOTOPE TESTS OF SEASALT CORRECTION FACTORS IN PRECIPITATION -NOVA-SCOTIA, CANADA

Sulphate in precipitation is an index of atmospheric pollution but nat ural sources also contribute to its concentration. One of the dominant natural sources of sulphate is seasalt and researchers have routinely calculated its proportion using reference species such as Cl-, Na+ an d Mg2+. Such a method of estimation assumes conservatism of, and a pur ely marine origin for, the reference species. The stable isotopes of s ulphur were utilized to assess the validity of these assumptions for a coastal area in Canada by taking advantage of the sulphur isotopic si gnature of seasalt sulphate (+20parts per thousand). The seaspray comp onent (PSS) was calculated for 39 coastal rain events using Cl-, Na+ a nd Mg2+ as reference species and these parameters were plotted against the sulphur isotopic composition of sulphate in the sample. All three regression lines yielded a value of almost-equal-to +4part per thousa nd for a sample containing no seasalt. The regression lines extrapolat ed to deltaS-34almost-equal-to+20, +17 and +16part per thousand using Cl-, Na+ and Mg2+ respectively for a theoretical sample whose sulphate was derived totally from seasalt. This observation confirms that for this locality, the marine component of precipitation sulphate utilizin g Cl- is isotopically equivalent to sea spray sulphate, suggesting tha t Cl- is a suitable reference species. It also supports the use of del taS-34(SO4) as a constraint on the selection of the correct reference species for estimation of the seasalt component in a particular study area.