Isotopic source signatures for atmospheric lead: the Northern Hemisphere

Aerosols collected between 1994 and 1999 at more than 70 different sites affecting the Southern Hemisphere have been measured for their 206Pb/207Pb, 208Pb/207Pb and 206Pb/204Pb ratios and Pb concentrations. Lower ratios are found at the southern tips of Africa, Australia and South America probably due to the supply of alkyllead from a common supplier such as Associated Octel. The ratios increase in a northerly direction probably due to a changing market share in alkyllead or an increasing industrial Pb contribution. The geographical variations in isotopic signatures made it possible to broadly characterize the different regions that influence the Southern Hemisphere. Brazil and Argentina exhibited 206Pb/207Pb, 208Pb/207Pb and 206Pb/204Pb ratios in aerosols of 1.141–1.184, 2.416–2.442 and 17.77–18.57, respectively. Mexican aerosols had values of 1.188–1.197, 2.452–2.463 and 18.46–18.73. Aerosols sampled in Chile had low ratios in the South of 1.063–1.094, 2.337–2.373 and 16.46–17.13 which increased in a northerly direction. Emissions from South Africa were characterized by ratios 1.067–1.090, 2.340–2.358 and 16.53–16.99. In 1994–1995 Australia and New Zealand had ratios of 1.060–1.193, 2.324–2.445 and 16.08–18.54. In 1997 however, the range was narrower: 1.072–1.112, 2.342–2.398 and 16.55–17.36, respectively. These isotopic signatures are potentially useful for tracing sources of pollution and the movement of air-masses on a global scale.