ISOTOPIC EVIDENCE FOR THE ORIGIN OF SULFATE IN COASTAL RAIN

Stable sulphur and oxygen isotopic analyses were combined with chemist ry, air mass back trajectories and factor analysis on 39 rainfall even ts collected at Shelburne, Nova Scotia, Canada in an attempt to identi fy the sources of sulphate in precipitation falling in this coastal ar ea. Sulphate in the Shelburne rain samples can be described by two-end member mixing between continental and oceanic sources. The continental endmember is characterized by delta(34)S approximate to 4 degrees/(oo ) and delta(18)O similar to 11 degrees/(oo) and is interpreted as repr esenting the average value for continentally-derived, long range trans ported sulphate. The marine endmember has 634S, 21 degrees/(oo) and de lta(18)O approximate to 9.5 degrees/(oo) corresponding to the composit ion of oceanic dissolved sulphate which entered the rain as sea spray. Significant components of putative marine, DMS-derived sulphate were not observed in any of the rain samples.