Tracing sources of precipitation sulfate in eastern Canada using stable isotopes and trace metals

Stable isotopic and chemical evidence has been used to trace sources of sul fate in precipitation in eastern Canada and to apportion this sulfate betwe en natural and anthropogenic origins. A site in Nepean, Ontario was chosen to characterize continental inputs from long-range transport, while two coa stal sites in Newfoundland (St. John's and Seal Cove) were chosen to repres ent the boundary between the marine and continental environments. Precipita tion sulfate at the coastal sites should reflect mixing of these two source areas, modified by contributions from local anthropogenic sources. The res ults of this study show that a three end-member isotopic mixing model using delta(18)O and delta(34)S describes the composition of sulfate at the Newf oundland sites. The three end-members are (1) sea spray (delta(34)S=+21 par ts per thousand; delta(18)O=+9.5 parts per thousand), (2) long-range transp orted secondary (anthropogenic) sulfate (delta(34)S similar to+4 parts per thousand; delta(18)O similar to 15 parts per thousand), and (3) local prima ry (anthropogenic) sulfate (delta(34)S delta similar to+49 parts per thousa nd; delta(18)O=+42 parts per thousand). Mass balance calculations show that as much as 63% of the sulfate deposited at the St. John's site and 18% at Seal Cove is primary sulfate emitted from local pollution sources. Up to 30 % of the sulfur deposited in rain at the Newfoundland sites is of continent al origin.