Isotopic evidence for the origin of sulphate in coastal rain

Stable sulphur and oxygen isotopic analyses were combined with chemistry, air mass back trajectories and factor analysis on 39 rainfall events collected at Shelburne, Nova Scotia, Canada in an attempt to identify the sources of sulphate in precipitation falling in this coastal area. Sulphate in the Shelburne rain samples can be described by two-endmember mixing between continental and oceanic sources. The continental endmember is characterized by δ³⁴S≈4‰ and δ18O≈11‰ and is interpreted as representing the average value for continentally-derived, long range transported sulphate. The marine endmember has δ34S≈21‰ and δ18O ≈ 9.5‰ corresponding to the composition 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.