Atmospheric Pb Deposition since the Industrial Revolution Recorded by Five Swiss Peat Profiles: Enrichment Factors, Fluxes, Isotopic Composition, and Sources

Abstract

Atmospheric Pb deposition since the Industrial Revolution was studied in western, central, and southern Switzerland using five rural peat bogs. Similar temporal patterns were found in western and central Switzerland, with two distinct periods of Pb enrichment relative to the natural background: between 1880 and 1920 with enrichments ranging from 40 to 80 times, and between 1960 and 1980 with enrichments ranging from 80 to 100 times. The fluxes also were generally elevated in those time periods: in western Switzerland between 1.16 and 1.55 μg cm-2 y-1 during the first period, and in western and central Switzerland between 0.85 and 1.55 μg cm-2 y-1 during the second period. Between the Industrial Revolution and 1985, nonradiogenic Pb became increasingly important in all five cores because of the replacement of coal by oil after ca. 1920, the use of Australian Pb in industry, and the extensive combustion of leaded gasoline after 1950. The introduction of unleaded gasoline in 1985 had a pronounced effect on the Pb deposition in all five cores. Enrichments dropped sharply (between 2 and 4 times), and the isotopic ratios reverted back toward (but not achieving) natural values. The cores from western and central Switzerland showed very similar isotopic trends throughout the time period studied, implying that these sites were influenced contemporaneously by similar pollution sources and atmospheric pathways. Southern Switzerland revealed a different record with respect to the Pb pollution: it was dominated by a single massive Pb enrichment dated between 1930 and 1950. During this period the Pb enrichment factor reached ∼200 times background and the Pb flux was ∼27 μg cm-2 y-1, more than an order of magnitude higher that at the western and central sites. This core also had significantly different post-1950 changes in the Pb isotope ratios.