Preprints
https://doi.org/10.5194/amt-2020-201
https://doi.org/10.5194/amt-2020-201

  04 Aug 2020

04 Aug 2020

Review status: a revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Application of the ECT9 protocol for radiocarbon-based source apportionment of carbonaceous aerosols

Lin Huang1, Wendy Zhang1, Guaciara M. Santos2, Blanca T. Rodríguez2, Sandra R. Holden2, Vincent Vetro1, and Claudia I. Czimczik2 Lin Huang et al.
  • 1Climate Research Division, Atmospheric Science & Technology Directorate, Environment and Climate Change Canada, Toronto, ON M3H 5T4, Canada
  • 2Department of Earth System Science, University of California, Irvine, CA 92697-3100, USA

Abstract. Carbonaceous aerosol is mainly composed of organic carbon (OC) and elemental carbon (EC). Both OC and EC originate from a variety of emission sources. Radiocarbon (14C) analysis can be used to apportion bulk aerosol, OC, and EC into their sources. However, such analyses require the physical separation of OC and EC.

Here, we apply of ECT9 protocol to physically isolate OC and EC for 14C analysis and evaluate its effectiveness. Several reference materials are selected, including: two pure OC (fossil adipic acid, contemporary sucrose), two pure EC (fossil regal black and C1150), and three complex materials containing contemporary and/or fossil OC and EC (rice char and NIST urban dust standards SRM1649a, i.e., bulk dust and SRM8785, i.e., fine fraction of re-suspended SRM1649a on filter). The pure materials were measured for their OC, EC and total carbon (TC) mass fractions and corresponding carbon isotopes to evaluate the uncertainty of the procedure. The average accuracy of TC mass, determined via volumetric injection of a sucrose solution, was approximately 5 %. Ratios of EC/TC and OC/TC were highly reproducible, with analytical precisions better than 2 % for all reference materials, ranging in size from 20 to 100 µg C. Consensus values were reached for all pure reference materials for both δ13C and FM14C with an uncertainty of < 0.3 ‰ and approximately 5&thnsp;%, respectively. The procedure introduced 1.3 ± 0.6 µg of extraneous carbon, an amount compatible to that of the Swiss_4S protocol.

14C values were reached for all OC (~ 5–30 µg) and EC (~ 10–60 µg) fractions with an uncertainty of < 5 %. We found that the ECT9 protocol efficiently isolates OC or EC from complex mixtures. Based on %delta;13C measurements, the average contribution of charred OC to EC is likely less than 3 % when the OC loading amount is less than 30 µg C.

Charring was further assessed by evaluating thermograms of various materials, including aerosol samples collected in the Arctic and from tailpipes of gasoline or diesel engines. These data demonstrate that the ECT9 method effectively removes pyrolyzed OC. Thus, the ECT9 protocol, initially developed for concentration and stable isotope measurements of OC and EC, is suitable for 14C-based apportionment studies for environment samples, including µg C-sized samples from Arctic environments.

Lin Huang et al.

 
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Lin Huang et al.

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Short summary
Radiocarbon (14C) -based source apportionment of aerosol carbon fractions requires the physical separation of OC from EC and minimizing the incorporation of extraneous carbon. Using pure and mixed reference materials ranging in age from modern to fossil, we show that the ECT9 protocol effectively isolates OC and EC. This work expands existing opportunities for characterizing and monitoring sources of carbonaceous aerosols, including µg C-sized samples from the Arctic.