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Central Asia is dominated by an arid climate and desert-like conditions, leading to the potential for long-range transport of desert dust within and out of the region. Of particular interest is the Aral Sea, which has receded in size largely due to water diversion. As a result, newly exposed sediments are resuspended by wind and thus, may be a potential new source of particulate matter within the region. Here, strontium and lead stable isotope ratios are employed 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, within Central Asia. Ambient PM 10 samples were collected during dust and non-dust events from mid-2008 to mid-2009 at two sites in Kyrgyzstan located ∼1200 and 1500 km ESE of the Aral Sea. Aral Sea sediments and local Kyrgyzstan soils were resuspended and sized to PM 10 . The Aral Sea sediments have an average 87 Sr/ 86 Sr ratio of 0.70992. In contrast, the Sr isotope ratio in local soils exhibits an average ratio of 0.71579. Ambient PM 10 collected in Kyrgyzstan has an average 87 Sr/ 86 Sr ratio of 0.71177, falling between the values of these two potential sources and indicating a complex mixture of contributing sources. At both sites, airborne Sr isotope ratios measured during dust events were similar, suggesting that Aral Sea sediments only minimally affect air quality in Kyrgyzstan. Elemental analysis and Pb isotope ratios supported this finding. While the Pb isotopes and elemental data both indicate an anthropogenic source, long-range dust transport from other deserts inside and outside the region cannot be ruled out as sources of PM 10 in Central Asia. [ABSTRACT FROM AUTHOR]

Abstract: Central Asia is a relatively understudied region of the world in terms of characterizing ambient particulate matter (PM) and quantifying source impacts of PM at receptor locations, although it is speculated to have an important role as a source region for long-range transport of PM to Eastern Asia, the Pacific Ocean, and the Western United States. PM is of significant interest not only because of its adverse effect on public health but also due to its more recently realized role in climate change. To investigate the sources and characteristics of PM in the region, a series of PM2.5 and PM10 samples were collected on an every-other-day basis at two sites (termed “Bishkek” and “Teploklyuchenka”) in the Central Asian nation of the Kyrgyz Republic (also known as Kyrgyzstan) for a full year from July 2008 to July 2009. These samples were analyzed using standard methods for mass, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), water-insoluble organic carbon by difference (OC minus WSOC) and a variety of molecular marker chemical species to be used in a chemical mass balance (CMB) model to apportion the sources of OC. These analyses indicate that approximately 19 ± 6.4% of the PM2.5 mass at both sites throughout the year consists of OC. The carbonaceous component of PM2.5 is dominated by OC, with OC/Total Carbon (TC) ratios being around 0.8 in the winter to almost 0.95 in the summer months. The CMB analysis indicated that mobile sources, i.e., gasoline and diesel engine exhaust, biomass combustion, and biogenic secondary organic aerosol (SOA) formation from isoprene and α-pinene precursors in the summer months were the dominant sources of OC. A strong positive correlation was observed between non-biomass burning WSOC and the un-apportioned OC from the CMB analysis, indicating that some of this un-apportioned OC is WSOC and likely the result of SOA-forming atmospheric processes that were not estimated by the CMB analysis performed. In addition, a comparison of the predominant contributors to OC between the two sites indicates that biomass combustion is a stronger relative source of OC at the Teploklyuchenka site, particularly in the winter, while contributions of isoprene- and α-pinene-derived SOA to the measured OC was relatively similar between the sites. [Copyright &y& Elsevier]