Intercomparison of 14C Analysis of Carbonaceous Aerosols: Exercise 2009

Abstract

ABSTRACT. Radiocarbon analysis of the carbonaceous aerosol allows an apportionment of fossil and non-fossil sources of airborne particulate matter (PM). A chemical separation of total carbon (TC) into its subfractions organic carbon (OC) and elemental carbon (EC) refines this powerful technique, as OC and EC originate from different sources and undergo different processes in the atmosphere. Although 14 C analysis of TC, EC, and OC has recently gained increasing attention, interlaboratory quality assurance measures have largely been missing, especially for the isolation of EC and OC. In this work, we present results from an intercomparison of 9 laboratories for 14 C analysis of carbonaceous aerosol samples on quartz fiber filters. Two ambient PM samples and 1 reference material (RM 8785) were provided with representative filter blanks. All laboratories performed 14 C determinations of TC and a subset of isolated EC and OC for isotopic measurement. In general, 14 C measurements of TC and OC agreed acceptably well between the laboratories, i.e. for TC within 0.015-0.025 F 14 C for the ambient filters and within 0.041 F 14 C for RM 8785. Due to inhomogeneous filter loading, RM 8785 demonstrated only limited applicability as a reference material for 14 C analysis of carbonaceous aerosols. 14 C analysis of EC revealed a large deviation between the laboratories of 28-79% as a consequence of different separation techniques. This result indicates a need for further discussion on optimal methods of EC isolation for 14 C analysis and a second stage of this intercomparison.

Evaluation and Inter-Comparison of Oxygen-Based OC-EC Separation Methods for Radiocarbon Analysis of Ambient Aerosol Particle Samples

“…The results presented in Figure 6 did not show a clear connection between the WIOC concentration of the filters or the EC recovery and the fraction modern of EC, but already a small amount of remaining OC can increase F 14 C(EC) significantly. [27], show a standard deviation for the uncorrected F 14 C(EC) data of 0.065 (Milan) and 0.117 (Ispra) for two ambient filter samples. F 14 C(EC) of ambient aerosol particle samples have been reported by previous studies [11,12,14,43] across Europe in a range from 0.1, mostly for filter samples from cities, to up to 0.8, measured during winter-time smog episodes related to wood burning in Switzerland [44].…”

“…The most recent and comprehensive inter-comparison exercise of 14 C in carbonaceous aerosols [27] found that results of 14 C measurements in OC and TC generally agree well between the different laboratories, but results for EC showed large differences ranging from 28-79%. These values represent the inter-laboratory standard deviation of 14 C in EC for three different samples.…”

Radiocarbon-based source apportionment of elemental carbon aerosols at two South Asian receptor observatories over a full annual cycle

“…A recent community inter-comparison of 14 C measurements on aerosol samples demonstrated comparable results for aerosol total carbon (Szidat et al 2013). There is a need for future such comparisons of different techniques and operational definitions for isolating the EC fraction for 14 C measurements.…”

Diurnal cycle of fossil and nonfossil carbon using radiocarbon analyses during CalNex

“…Radiocarbon analysis ( 14 C) is a quantitative tool for unambiguously distinguishing fossil and nonfossil sources of EC and OC. 14 C is completely depleted in fossil fuel emissions ( 14 C half-life = 5730 years), which can therefore be separated from nonfossil carbon sources (e.g., biomass burning, cooking, or biogenic emissions) which have a similar amount of 14 C as atmospheric carbon dioxide (CO 2 ) [Szidat, 2009;Currie, 2000]. The 14 C measurement on the EC fraction is still challenging.…”