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Stable isotopes of lead and strontium as tracers of sources of airborne particulate matter in Kyrgyzstan.
Dewan, N., B. Majestic, M. Ketterer, J. Miller-Schulze, M. Shafer, J. Schauer, P. Solomon, M. Artamonova, B. Chen, S. Imashev, AND G. Carmichael. Stable isotopes of lead and strontium as tracers of sources of airborne particulate matter in Kyrgyzstan. 249th ACS National Meeting & Exposition, Denver, CO, March 22 - 26, 2015.
The National Exposure Research Laboratory (NERL) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA mission to protect human health and the environment. HEASD research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools is improved regulatory programs and policies for EPA.
Central Asia is dominated by an arid climate and desert-like conditions, leading to the potential of long-range transport of desert dust. One potential source of dust to Central Asia is the Aral Sea, the surface area of which has receded in size from 68,000 km2 to 14,280 km2, largely as the result of water diversion. As a result, newly exposed sediments are resuspended by the wind and are a new source of PM, which may impact human health and climate. We employed Sr and Pb stable isotope ratios, along with detailed elemental composition, to explore the contribution of long-range transport of Aral Sea sediments, as well as other potential sources of dust to Central Asia. A detailed series of PM10 samples from two sites (Bishkek and LIDAR) in Kyrgyzstan (the “receptor” sites, located ~1,200 and 1,500 km WSW of the Aral Sea), along with resuspended Aral Sea sediments and local soils near the monitoring sites were collected in 2008-2009, both during dust storm events and non-dust events. The average 87Sr/86Sr ratio of the Aral Sea sediments was found to be 0.70992 (0.70951-0.71064). In contrast, the Sr isotope ratio in the local soils in Kyrgyzstan is dominated by the weathering of native rocks, exhibiting an average 87Sr/86Sr ratio of 0.71579 (0.71448-0.71739), which is significantly different than the Aral Sea sediments. The PM collected in Kyrgyzstan have an average 87Sr/86Sr ratio of 0.71177 (0.70946-0.71335), indicating a complex mixture of contributions, which may include long-range transport of Aral Sea sediments, dusts from regional deserts, and local soils. Similar Sr isotope ratios were observed during the dust events and non-dust events at both sites, indicating that the Aral Sea sediments only have a minimal effect to air quality in Kyrgyzstan. Elemental analysis and Pb isotope ratios were helpful in refining the source regions. The K/Pb ratios ranged from 46-112 and for sediments and native soils, and from 775-863 for the ambient PM10, which suggests that the airborne PM contains a significant fraction of anthropogenic Pb. Stable Pb isotope ratios confirm that, although the Aral Sea region may be a minor source of aerosol Pb in Kyrgyzstan, there is at least one other source that was not measured in this study. While the isotope and elemental data both indicate an anthropogenic source, long-range dust transport from Africa or the Middle East cannot be ruled out as sources of PM to Central Asia.