Evaluation of a protocol for the quantification of black carbon in sediments

Abstract

Abstract. Formation of highly condensed black carbon (BC) from vegetation fires and wood fuel combustion presumably transfers otherwise rapidly cycling carbon from the atmosphere-biosphere cycle into a much slower cycling geological form. Recently reported BC fractions of total organic carbon (TOC) in surficial marine sediments span a wide range (2-90%), leaving it presently unclear whether this variation reflects natural processes or is largely due to method differences. In order to elucidate the importance of BC to carbon burial the specificity of applied methods needs to be constrained. Here the operating range and applicability of a commonly used chemothermal oxidation (CTO) method is evaluated using putative BC standards, potentially interfering substances, and natural matrix standards. Test results confirm the applicability of the method to marine sediments. Integrity tests with model substrates suggest applicability to low-carbon soils but only with a lower specificity to seawater particulate matter. The BC content of marine sediment samples in a set of studies employing the CTO method proved to be consistent with associated geochemical information. The radiocarbon content of the BC isolate in an environmental matrix standard was shown to be similar to the radiocarbon signature of pyrogenic polycyclic aromatic hydrocarbons (PAHs), here serving as molecular markers of combustion (fraction modemfM of BC was 0.065 + 0.014 and of PAHs 0.056 + 0.020), while being clearly distinct from the radiocarbon content of the bulk TOC (fM= 0.61 + 0.08). Urgent questions such as the global accumulation rate of black carbon in soils and sediments may prove approachable with the chemothermal oxidation technique of BC quantification.

Visualizing the mobility of silver during catalytic soot oxidation

“…The identity of the silver sample was verified by X-Ray diffraction ( Figure S1 in the Supplementary Information). The soot used in the experiments was a reference material from NIST: "SRM 2975 Diesel Particulate Matter" (91 m 2 /g, 86-87 wt% C, 1-2 wt% H, ~1 wt% S, 2.7 wt% extractable organics [19,[34][35][36]). …”

Stability and carbon isotope changes of soot and char materials during thermal oxidation: Implication for quantification and source appointment

“…The contents of BC in seven soot and char samples and their thermal stability were quantified with a CTO operated at different temperature conditions (Gustafsson et al, 1997(Gustafsson et al, , 2001Accardi-Dey, 2003;Elmquist et al, 2006). In brief, about 5-10 mg of each sample (duplicates, dried and ground to ≤100 μm) were weighed and placed in silver capsules (4.5 × 6.0 mm, Xinda Analytical, Taiyuan, China).…”

“…BC materials are broadly categorized into two groups: soot-BC and char-BC. Soot-BC consists of sub-micron particles formed at high combustion temperatures via condensation of hydrocarbons, followed by the growth and stacking of aromatic layers (Ishiguro et al, 1997;Schmidt and Noack, 2000;Gustafsson et al, 2001). Char-BC consists of larger particles formed at relative lower temperatures from incomplete combustion of wood or other organic materials (Goldberg, 1985;Schmidt and Noack, 2000;Fernandes et al, 2003;Nguyen et al, 2004).…”

“…It is ubiquitous in the atmosphere, soil, sediment, and water, and is increasingly recognized for its important roles in the atmospheric chemistry, global carbon cycle, and fate of organic pollutants (Goldberg, 1985;Kuhlbusch, 1998;Gustafsson and Gschwend, 1998;Schmidt and Noack, 2000;Gustafsson et al, 2001;Jacobson, 2001;Song et al, 2002;Accardi-Dey and Gschwend, 2002;Accardi-Dey, 2003;Masiello, 2004;Xiao et al, 2004;Cornelissen et al, 2005;Hammes et al, 2007). BC materials are broadly categorized into two groups: soot-BC and char-BC.…”

“…Several laboratory procedures including light microscopy, scanning and transmission electron microscopy, thermooptical transmission, and chemical and/or thermal oxidation followed by quantification with FTIR, molecular tracer proxies, or elemental analyses were used in the literature for quantifying BC in environmental samples (Lim and Cachier, 1996;Gustafsson et al, 1997Gustafsson et al, , 2001Song et al, 2002;Brodowski et al, 2005;Hammes et al, 2007). Among these tested methods, the chemothermal oxidation (CTO) method has gained much attention as operatively simple and reasonably accurate measurements for soot-BC in soils and sediments (Gustafsson et al, 1997(Gustafsson et al, , 2001Gélinas et al, 2001;Elmquist et al, 2004Elmquist et al, , 2006 and later also soot-BC in aerosols (Zencak et al, 2007;Gustafsson et al, 2009). For instance, the large-scale distribution of combustion-derived and sorptive PAHs in marine sediments have repeatedly been shown to be much better explained by CTO375-based BC than by bulk OC or any other parameter (e.g., Gustafsson and Gschwend, 1998;Persson et al, 2002;Oen et al, 2006;Sanchez-Garcia et al, 2010).…”