10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Strontium and Lead Stable Isotopes as Tracers of PM2.5 in Northern India
RACHEL YORK-MARINI, Swati Sharma, Gazala Habib, Brian Majestic, University of Denver
Abstract Number: 1038 Working Group: Source Apportionment
Abstract The World Health Organization’s 2006 Air Quality Standards recommend a 24 hour mean concentration of 25 µg/m3 for PM2.5. On January 1, 2018, Delhi, India surpassed these guidelines with PM levels of 431 µg/m3. While vehicular emissions are one of the leading sources of pollution in Delhi, smaller dust particles may be transported from the nearby Thar Desert and contribute to PM2.5 concentrations in Delhi. Strontium and lead stable isotopes, which are highly specific to unique geographical areas, along with trace element composition, are ideal metrics to source dust in atmospheric PM. Here, we use these isotope systems to understand whether the nearby Thar Desert is an important dust source for Delhi and Jaipur. We collected PM2.5 from two cities in the northern Indian plains: Delhi and Jaipur, India between June and December 2015. This included both the monsoon and non-monsoon seasons. Additionally, soil samples were collected from both cities and from the Thar Desert, and were resuspended to PM2.5. All PM and soil samples were acid digested and analyzed for 35 trace elements via ICP-MS. The remainder of the digests were used to measure strontium and lead isotopic composition via MC-ICP-MS, for the purposes of dust tracing.
Elemental composition varied between Delhi and Jaipur, with many trace elements in Jaipur having lower concentrations than Delhi. Trace elements Sn, Zn, Cr, Ni, Sb, and As had concentrations of 0.143, 0.172, 0.010, 0.006, 0.0034, and 0.0015 µg/m3, respectively, in Delhi and 0.0017, 0.336, 0.0018, 0.0025, 0.0011, and 0.001 µg/m3, respectively in Jaipur. The dominant elemental components of the PM in Delhi were crustal elements Al, K, Ca, and Fe with average concentrations of 0.788, 0.445, 0.431, and 0.541 µg/m3, respectively. In Jaipur, crustal elements Al, K, Ca, and Na with average concentrations of 0.593, 0.326, 7.691, and 0.446 µg/m3, respectively, were the dominant sources of PM. The Delhi PM2.5 samples had an 87Sr/86Sr average ratio of 0.7165 ± 0.0012 (uncertainties = +/- 1 standard deviation of all data). Delhi and Thar soil samples had an average 87Sr/86Sr ratio of 0.7155 ± 0.0015. The Jaipur aerosol samples had an average 87Sr/86Sr ratio of 0.720 ± 0.012, while the Jaipur soil samples had an average of 0.7195 ± 0.0006. The results of 87Sr/86Sr ratios and 1/Sr µg/g indicate that strontium in Delhi is coming from multiple sources. Delhi and Jaipur aerosol samples had an average 207Pb/206Pb ratio of 0.893 ± 0.005 and 0.8888 ± 0.0025 respectively, whereas the Delhi and Thar Desert soils had an average 207Pb/206Pb ratio of 0.833 ± 0.009 and Jaipur soils had an average 207Pb/206Pb ratio of 0.8379 ± 0.0018. This, along with no linear correlation between thallium and lead, indicates the source of lead is anthropogenic.