A stable isotopic study of natural and anthropogenic sulphur in precipitation in eastern Canada

Jamieson, Robyn Elizabeth (1995) A stable isotopic study of natural and anthropogenic sulphur in precipitation in eastern Canada. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (65MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Event rain samples were collected at three sites in eastern Canada in an attempt to characterize the sources of sulphate in precipitation utilizing the isotopic signatures of sulphur and oxygen. Both continental and marine sites were chosen providing an opportunity to compare these different environments. Sulphur isotopes are useful tools for source tracing because they undergo little fractionation subsequent to emission to the atmosphere. Oxygen isotopes are useful for examining processes of oxidation which occur during transport and deposition of sulphur. A unique feature of this study is the incorporation of trace metal and meteorological data along with isotopic evidence to further aid source identification. -- Three sites were chosen for this study representing marine/urban (St. John's, NF), marine/rural (Seal Cove, NF), and continental/rural (Nepean, ON) environments. The sulphur isotopic results at both marine sites are best described by two end-member mixing between a seaspray end-member (+21%o) and a low δ³⁴S end-member (≈ +5%o). The low δ³⁴S end-member likely represents a mixture of long-range transported continental and local anthropogenic sources. Oxygen values also reflect a seaspray end-member (+9.5%o) and a continental end-member (+10 to +12%o), however the St. John's data contain a significant ¹⁸O-enriched pollution input. Despite its proximity to a thermal generating station, the Seal Cove site is apparently free from a strong local pollution source, but some locally oxidized secondary sulphate is evident from the correlation between δ¹⁸Oso₄ and δ¹⁸OH₂o. The Nepean site has a very different character because of its continental nature. It exhibits a constant isotopic signature with an average δ³⁴S value of +4.4%o and an average δ¹⁸Oso₄ value of +14.7%o. Local oxidation is not important at this site. Since the region is relatively unpolluted, primary sulphates must have been transported from other areas. The average δ³⁴S value for Nepean is the same as the low δ³⁴S end-members of St. John's and Seal Cove, suggesting that eastern North America may be the source of the continental/anthropogenic signal seen at the coastal sites. -- A significant contribution of this study has been the measurement of extremely high δ¹⁸Oso₄ values (+42%o) at St. John's, much higher than those measured in other studies. These ¹⁸O-enriched sulphates are in samples with elevated metal concentrations (Ni, V, Mo, Co, Cu, Mn) and represent primary sulphates formed by the high temperature processes associated with combustion in the power plant located near the site. Previous researchers predicted that primary sulphates would exhibit extremely high oxygen isotopic compositions, and this work is the first to confirm this in natural rain samples. -- This investigation has provided insight on how interaction between long-range transported continental, marine and local sulphur sources defines the character of individual sites. It has also demonstrated how isotopic and chemical data can be successfully combined to give a complete picture of the sources of sulphur affecting a particular.

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