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| Titel |
Accuracy and precision of 14C-based source apportionment of organic and elemental carbon in aerosols using the Swiss_4S protocol |
| VerfasserIn |
G. O. Mouteva, S. M. Fahrni, G. M. Santos, J. T. Randerson, Y.-L. Zhang, S. Szidat, C. I. Czimczik |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 9 ; Nr. 8, no. 9 (2015-09-16), S.3729-3743 |
| Datensatznummer |
250116576
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| Publikation (Nr.) |
 copernicus.org/amt-8-3729-2015.pdf |
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| Zusammenfassung |
| Aerosol source apportionment remains a critical challenge for understanding
the transport and aging of aerosols, as well as for developing successful
air pollution mitigation strategies. The contributions of fossil and
non-fossil sources to organic carbon (OC) and elemental carbon (EC) in
carbonaceous aerosols can be quantified by measuring the radiocarbon
(14C) content of each carbon fraction. However, the use of 14C in
studying OC and EC has been limited by technical challenges related to the
physical separation of the two fractions and small sample sizes. There is no
common procedure for OC/EC 14C analysis, and uncertainty studies have
largely focused on the precision of yields. Here, we quantified the
uncertainty in 14C measurement of aerosols associated with the
isolation and analysis of each carbon fraction with the Swiss_4S thermal–optical analysis (TOA) protocol. We used an OC/EC analyzer
(Sunset Laboratory Inc., OR, USA) coupled to a vacuum line to separate the
two components. Each fraction was thermally desorbed and converted to carbon
dioxide (CO2) in pure oxygen (O2). On average, 91 % of the
evolving CO2 was then cryogenically trapped on the vacuum line, reduced
to filamentous graphite, and measured for its 14C content via
accelerator mass spectrometry (AMS). To test the accuracy of our setup, we
quantified the total amount of extraneous carbon introduced during the TOA
sample processing and graphitization as the sum of modern and fossil
(14C-depleted) carbon introduced during the analysis of fossil
reference materials (adipic acid for OC and coal for EC) and contemporary
standards (oxalic acid for OC and rice char for EC) as a function of sample
size. We further tested our methodology by analyzing five ambient airborne
particulate matter (PM2.5) samples with a range of OC and EC
concentrations and 14C contents in an interlaboratory comparison. The
total modern and fossil carbon blanks of our setup were 0.8 ± 0.4 and 0.67 ± 0.34 μg C, respectively, based on
multiple measurements of ultra-small samples. The extraction procedure
(Swiss_4S protocol and cryo-trapping only) contributed 0.37 ± 0.18 μg of modern carbon and 0.13 ± 0.07 μg of
fossil carbon to the total blank of our system, with consistent estimates
obtained for the two laboratories. There was no difference in the background
correction between the OC and EC fractions. Our setup allowed us to
efficiently isolate and trap each carbon fraction with the
Swiss_4S protocol and to perform 14C analysis of
ultra-small OC and EC samples with high accuracy and low 14C blanks. |
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