Lead isotope tracking of atmospheric response to post-industrial conditions in Yerevan, Armenia

Temporal gradients in environmental lead concentrations and isotopic compositions trace the rapidly shifting transition from high to low industrial emissions in Yerevan, Armenia following the dissolution of the Soviet Union in the early 1990s. Shortly after the breakup, in 1995 and 1996, atmospheric lead concentrations averaged 0.4 μg m−3 and the combustion of leaded gasoline was the primary source of industrial lead emissions in Yerevan. But by 1998, unleaded gasoline was predominant and atmospheric lead concentrations had decreased by two orders of magnitude to 0.003 μg m−3 because industrial lead emissions from stationary sources had also been radically curtailed. The increased proportion of unleaded gasoline use is clearly seen in comparisons of the isotopic compositions of lead in air and gasoline. In 1998 and 1999, the isotopic composition of atmospheric lead (1.1605 206Pb/207Pb 1.1641) was comparable to that in soil (1.1357 206Pb/207Pb 1.1649); and it was markedly different from the average isotopic value of gasoline (206Pb/207Pb=1.1407 in 1998 and 1.1555 in 1999). Binary mixing calculations suggest that 75% of the atmospheric lead in 1998 was derived from re-suspended soil that retains lead from past emissions and 25% was derived from a mixture of present industrial emissions and uncontaminated soil. Anthropogenic lead persists in urban air, albeit at relatively low levels, despite leaded gasoline phase out and stationary emissions curtailment.