Sr-Nd-Hf isotopic analysis of reference materials and natural and anthropogenic particulate matter sources: Implications for accurately tracing North African dust in complex urban atmospheres

Coupling Sr–Nd–Hf Isotope Ratios and Elemental Analysis to Accurately Quantify North African Dust Contributions to PM2.5 in a Complex Urban Atmosphere by Reducing Mineral Dust Collinearity

“…Forty-nine elements (Li, Be, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Zr, Mo, Cd, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Pb, Th, and U) were analyzed by quadrupole ICP–MS equipped with a collision cell pressurized with ammonia gas (NH 3 ) (PerkinElmer NexION 300) after solubilization by two-stage microwave digestion . Sr, Nd, and Hf isotopes were analyzed by Multi-Collector ICP–MS (MC-ICP-MS) after column separation chemistry . For ease of comparison and as is the convention, Nd and Hf isotopic ratios were expressed as deviation from the chondritic uniform reservoir (CHUR, 176 Hf/ 177 Hf = 0.282785 and 143 Nd/ 144 Nd = 0.512630).…”

“…Applicable elemental source profiles included soil/road dust, concrete dust, , motor vehicles, , fluidized-bed cracking catalysts (FCCs) representing primary petroleum refinery emissions, , oil and coal combustion, , biomass burning, , and sea salt, based on previous reports in Houston. ,,,,, The trans-Atlantic North African dust profile was established during this work (Table S15). The IRCMB method balances both elements (eq ; conventional CMB) and isotopes (this study; eq )­ where C i is the ambient concentration of the i th element, F ij is the abundance of the i th element in the j th source, S j is the source contribution j th source to ambient PM 2.5 , is the isotope ratio of the j th source corresponding to isotope i (Sr, Nd, and Hf in our case), and R̂ i is the isotope ratio corresponding to element i .…”

“…Inclusion of isotope ratios (eq ) in the dataset reduced the CI from 27 to 21. Here, Na, Mg, Al, Si, K, Ca, Ti, V, Fe, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, La, Ce, Nd, Hf, and Pb were used as fitting species because of their importance in tracing PM sources in Houston. ,,,,,, The dataset was reprocessed to reduce collinearity even further.…”

“…Significant uncertainties are introduced during source apportionment of primary PM when potential tracers are coemitted by multiple sources or there is overlap in the composition of potential sources, especially when allocating low mass contributions. , For example, it is difficult to separate North African dust and non-African local soil at receptor sites since they both represent crustal material consequently possessing similar elemental composition. ,, Another concern is dust emanating from construction activities, which is composed largely of mineral materials lacking unique markers, , thereby leading to unreliable results when using receptor-based source apportionment models.…”

“…Of relevance to this article, only limited information is available on using 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios to trace the geological origins of dust in remote − and urban , regions of the world. Coupling Hf isotopes to Sr and/or Nd enhances the accuracy of isolating long-range transported natural dust sources − based on differing isotope ratios due to variations in source bedrock (Sr–Nd) and zircon depletion (Hf–Nd) during transport, ,,,, which has been studied solely in remote locations until now.…”