Black Carbon Continuum Research Articles

From Bulk to Nano: Formation, Features, and Functions of Nano-Black Carbon in Biogeochemical Processes.

Globally increasing wildfires and widespread applications of biochar have led to a growing amount of black carbon (BC) entering terrestrial ecosystems. The significance of BC in carbon sequestration, environmental remediation, and the agricultural industry has long been recognized. However, the formation, features, and environmental functions of nanosized BC, which is one of the most active fractions in the BC continuum during global climate change, are poorly understood. This review highlights the formation, surface reactivity (sorption, redox, and heteroaggregation), biotic, and abiotic transformations of nano-BC, and its major differences compared to other fractions of BC and engineered carbon nanomaterials. Potential applications of nano-BC including suspending agent, soil amendment, and nanofertilizer are elucidated based on its unique properties and functions. Future studies are suggested to develop more reliable detection techniques to provide multidimensional information on nano-BC in environmental samples, explore the critical role of nano-BC in promoting soil and planetary health from a one health perspective, and extend the multifield applications of nano-BC with a lower environmental footprint but higher efficiency.

Opening the black box: Soil microcosm experiments reveal soot black carbon short-term oxidation and influence on soil organic carbon mineralisation

Soils hold three quarters of the total organic carbon (OC) stock in terrestrial ecosystems and yet we fundamentally lack detailed mechanistic understanding of the turnover of major soil OC pools. Black carbon (BC), the product of the incomplete combustion of fossil fuels and biomass, is ubiquitous in soils globally. Although BC is a major soil carbon pool, its effects on the global carbon cycle have not yet been resolved. Soil BC represents a large stable carbon pool turning over on geological timescales, but research suggests it can alter soil biogeochemical cycling including that of soil OC. Here, we established two soil microcosm experiments: experiment one added 13C OC to soil with and without added BC (soot or biochar) to investigate whether it suppresses OC mineralisation; experiment two added 13C BC (soot) to soil to establish whether it is mineralised in soil over a short timescale. Gases were sampled over six-months and analysed using isotope ratio mass spectrometry. In experiment one we found that the efflux of 13C OC from soil decreased over time, but the addition of soot to soil significantly reduced the mineralisation of OC from 32% of the total supplied without soot to 14% of the total supplied with soot. In contrast, there was not a significant difference after the addition of biochar in the flux of 13C from the OC added to the soil. In experiment two, we found that the efflux 13C from soil with added 13C soot significantly differed from the control, but this efflux declined over time. There was a cumulative loss of 0.17% 13C from soot over the experiment. These experimental results represent a step-change in understanding the influence of BC continuum on carbon dynamics, which has major consequences for the way we monitor and manage soils for carbon sequestration in future.

Rapid and economical quantification of black carbon in soils using a modified benzene polycarboxylic acids (BPCA) method

Black carbon, the ubiquitous stable product of incomplete combustion, is a potential sink for atmospheric CO2 and, therefore, a contributor to the Earth’s radiative heat balance. Accurate information about the distribution of black carbon in soils is important for climate change projections, given that the black carbon content of soils varies widely across the globe. In response to this issue, an accurate, rapid and cost-effective method to assess BC is needed. The use of benzene polycarboxylic acids (BPCA) as molecular markers of black carbon has the advantage of specifically tracking the polyaromatic backbone of the black carbon continuum. However, this method has three major disadvantages: (a) it is expensive; (b) it is very time-consuming; and (c) some of the literature states that care has to be taken when applying the BPCA method to organic-rich matrices. In response to these disadvantages, the aims of the present study were: (a) to check the validity of a new shorter and economical method for black carbon quantification based on BPCA as molecular markers; and (b) to study the correlation between BPCA formation during the analysis and the soil sample’s OC content. The proposed method for black carbon quantification is based on the BPCA method developed by Glaser et al. (1998), but uses a simple direct elemental analysis (EA) of C content in the residue obtained after a strong digestion instead of the molecular determination by gas chromatography with flame ionisation detector (GC-FID). This simplification of the method represents a great cost reduction (in time and expense) providing a rapid and accurate method for large soil sample sets.

Mineral-associated organic carbon and black carbon in restored wetlands

Stable soil organic carbon (SSOC) has a vital influence on soil's capacity for resisting disturbance and sequestering carbon. However, studies of the SSOC in restored wetlands are incomplete. We studied mineral-associated organic carbon (MOC) and black carbon (BC), two representatives of SSOC, in a wetland restoration chronosequence in Caizi Lake, East China. MOC was analyzed by both a physical method, involving dividing soil into size-fractions POM (>53 μm) and MOM (0.45–53 μm) and detecting OC in MOM (MOCP), and a chemical method, acidifying soil with hydrofluoric acid (HF) and detecting OC loss (MOCC). BC was analyzed by methods using dichromate (BCCr) and chemothermal oxidation (BCCTO). MOCC, BCCr, and BCCTO were further determined in MOM for comparing results from different fractions and methods. We found an elevation of soil ecological function in wetlands restored from farmlands in Caizi Lake, which was supported by a general increase of MOC and BC with time after restoration at surface soil (0–6 cm). Comparison of methods showed that size fractionation method overestimated MOC by identifying all OC in MOM as MOC, since HF-soluble OC accounted for no more than 23.5% of the whole OC in MOM. As it may separate more components, e.g. charcoal, from BC continuum, the dichromate method was recommended as more meaningful in the study of BC recovery in restored wetlands with biomass-burning history. We presented the possible use of ratio (BCCr–BCCTO):BCCTO for BC source identification which produced a reasonable result similar to that of a commonly used method. The combination of physical and chemical fractionation methods revealed that the proportion of BC to TOC in POM was considerable, which indicated that POM was not invariably labile as was commonly understood. Finally, a detailed list of soil organic carbon components including MOC, BC and labile OC in each size fraction was represented by using sequential analysis and combination of fractionation methods.

Validation and application of a thermal–optical reflectance (TOR) method for measuring black carbon in loess sediments

Three techniques were used to measure black carbon (BC) in samples from Chinese loess-paleosol sequences. The results obtained by (1) chemo-thermal oxidation (CTO, performed two ways), (2) acid dichromate oxidation (Cr2O7), and (3) thermal–optical reflectance (TOR) were intercompared because prior studies have shown that the methods can yield disparate results. BC concentrations did vary among the methods, most likely because they measured different components of the BC continuum, but the high-temperature BC (soot) determined by CTO was correlated with the BC and soot obtained by TOR. The CTO and TOR methods both yielded statistically significant linear relationships for loess and lake sediments that had incremental additions of a standard (SRM-1649a). The results also showed that charred material was more abundant in these test sediments than soot carbon. Data for BC in Luochuan loess generated using TOR showed a trend similar to that of magnetic susceptibility, that is, high BC and large susceptibilities during the last interglacial and low values for both variables in the last glacial. The results thus indicate that the TOR method is well suited for studies of sedimentary materials and that more biomass burned during the last interglacial than in the last glacial.

Direct evidence from hydropyrolysis for the retention of long alkyl moieties in black carbon fractions isolated by acidified dichromate oxidation

Chemical oxidation with acidified potassium dichromate is one of the more commonly used of a range of available methods for the quantification of black carbon (BC) in soils and sediments. There are potential uncertainties with this method however, with indications that not all non-BC material is susceptible to oxidation. An emerging approach to BC quantification is hydropyrolysis (hypy), in which pyrolysis assisted by high hydrogen pressure facilitates the reductive removal of labile organic matter, so isolating a highly stable portion of the BC continuum that is predominantly composed of >7 ring aromatic domains.Here, results from the hypy of the BC fraction isolated by dichromate oxidation (BCdox) from a BC-rich soil are presented, which demonstrated that 88% of the total carbon initially defined as BC was stable under hypy conditions (defined as BChypy). More notably, hypy allowed the non-BChypy fraction to be characterised. In addition to a number of PAHs, the non-BChypy fraction was also found to contain a significant abundance of n-alkanes, with a marked predominance of even-numbered homologues. These compounds are probably derived from lipids, hydrogenated during hypy, which survived dichromate oxidation due to their hydrophobic nature. Hypy of the dichromate oxidation residue from a sample of Green River shale, known to contain no BC of pyrogenic origin revealed that the significant apparent BCdox content (BC/OC=5.7%) was also largely due to the presence of n-alkanes within the oxidation residues. The distribution of these compounds, biased towards longer chain homologues with no significant even/odd preference, indicated that they were largely derived from long n-alkyl chains within this highly aliphatic matrix.Hypy therefore provides compelling direct evidence for the incomplete removal of non-BC material by dichromate oxidation from both a BC-rich soil and a BC-free oil shale, with the molecular characterisation of the non-BChypy fraction allowing the potential sources of this material to be deduced.

Assessment of hydropyrolysis as a method for the quantification of black carbon using standard reference materials

A wide selection of thermal, chemical and optical methods have been proposed for the quantification of black carbon (BC) in environmental matrices, and the results to date differ markedly depending upon the method used. A new approach is hydropyrolysis (hypy), where pyrolysis assisted by high hydrogen pressures (150bar) facilitates the complete reductive removal of labile organic matter, so isolating a highly stable portion of the BC continuum (defined as BChypy). Here, the potential of hypy for the isolation and quantification of BC is evaluated using the 12 reference materials from the International BC Ring Trial, comprising BC-rich samples, BC-containing environmental matrices and BC-free potentially interfering materials. By varying the hypy operating conditions, it is demonstrated that lignocellulosic, humic and other labile organic carbon material (defined as non-BChypy) is fully removed by 550°C, with hydrogasification of the remaining BChypy not commencing until over 575°C. The resulting plateau in sample mass and carbon loss is apparent in all of the environmental samples, facilitating BC quantification in a wide range of materials. The BChypy contents for all 12 ring trial samples fall within the range reported in the BC inter-comparison study, and systematic differences with other methods are rationalised.All methods for BC isolation, including hypy are limited by the fact that BC cannot be distinguished from extremely thermally mature organic matter; for example in high rank coals. However, the data reported here indicates that BChypy has an atomic H/C ratio of less than 0.5 and therefore comprises a chemically well-defined polyaromatic structure in terms of the average size of peri-condensed aromatic clusters of >7 rings (24 carbon atoms), that is consistent across different sample matrices. This, together with the sound underlying rationale for the reductive removal of labile organic matter, makes hypy an ideal approach for matrix independent BC quantification. The hypy results are extremely reproducible, with BChypy determinations from triplicate analyses typically within ±2% across all samples, limited mainly by the precision of the elemental analyser.

Biochar: A Synthesis of Its Agronomic Impact beyond Carbon Sequestration

Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalties may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.

Comparison of gas with liquid chromatography for the determination of benzenepolycarboxylic acids as molecular tracers of black carbon

Existing methods for black carbon (BC) quantification measure different parts of the BC continuum, which complicates the calculation of a global BC budget. Benzenepolycarboxylic acids (BPCA) are used as molecular markers to quantify and characterize BC in soils and sediments using gas chromatography for BPCA separation (GC-BPCA). Recently, this method was refined for BC analysis in seawater using high performance liquid chromatography (LC-BPCA), which omits the cleaning steps and derivatization necessary in GC analysis. As yet it is not clear whether the two analytical methods yield similar results. Here we apply both methods to a suite of laboratory produced charcoals derived from wood and grass. We found systematically lower total BPCA-C contents and larger analytical variability for all tested charcoals when using GC-BPCA compared to LC-BPCA, the latter giving 1.5 ± 0.3 times higher yields for the charcoal samples formed at 275–700 °C. At lower and higher pyrolysis temperatures the differences between the two analytical methods were larger. The main reason for the differences between the two methods is the loss of BPCA during sample preparation for GC analysis. We propose a correction factor of 1.5 to account for at least part of these losses. No qualitative biases, i.e. towards more or less functionalized BPCAs, were observed between the two methods. The relative contribution of mellitic acid C to total BPCA-C, a measure for the degree of condensation of BC, was the same in the two analytical techniques. Qualitative differences between wood and grass charcoals as detected by both methods were small.

Impact of Biochar on Earthworm Populations: A Review

Despite the overwhelming importance of earthworm activity in the soil system, there are a limited number of studies that have examined the impact resulting from biochar addition to soil. Biochar is part of the black carbon continuum of chemo-thermal converted biomass. This review summarizes existing data pertaining to earthworms where biochar and other black carbon substances, including slash-and-burn charcoals and wood ash, have been applied. After analyzing existing studies on black carbon, we identified that these additions have a range from short-term negative impacts to long-term null effects on earthworm population density and total biomass. Documented cases of mortality were found with certain biochar-soil combinations; the cause is not fully understood, but hypothesized to be related to pH, whether the black carbon is premoistened, affects feeding behaviors, or other unknown factors. With wood ashes, negative impacts were overcome with addition of other carbon substrates. Given that field data is limited, soils amended with biochar did not appear to cause significant long-term impacts. However, this may indicate that the magnitude of short-term negative impacts on earthworm populations can be reduced with time.

14C-Based source assessment of soot aerosols in Stockholm and the Swedish EMEP-Aspvreten regional background site

Combustion-derived soot or black carbon (BC) in the atmosphere has a strong influence on both climate and human health. In order to propose effective mitigation strategies for BC emissions it is of importance to investigate geographical distributions and seasonal variations of BC emission sources. Here, a radiocarbon methodology is used to distinguish between fossil fuel and biomass burning sources of soot carbon (SC). SC is isolated for subsequent off-line 14 C quantification with the chemothermal oxidation method at 375 °C (CTO-375 method), which reflects a recalcitrant portion of the BC continuum known to minimize inadvertent inclusion of any non-pyrogenic organic matter. Monitored wind directions largely excluded impact from the Stockholm metropolitan region at the EMEP-Aspvreten rural station 70 km to the south-west. Nevertheless, the Stockholm city and the rural stations yielded similar relative source contributions with fraction biomass ( f biomass ) for fall and winter periods in the range of one-third to half. Large temporal variations in 14 C-based source apportionment was noted for both the 6 week fall and the 4 month winter observations. The f biomass appeared to be related to the SC concentration suggesting that periods of elevated BC levels may be caused by increased wood fuel combustion . These results for the largest metropolitan area in Scandinavia combine with other recent 14 C-based studies of combustion-derived aerosol fractions to suggest that biofuel combustion is contributing a large portion of the BC load to the northern European atmosphere.

Inferring Black Carbon Concentrations in Particulate Organic Matter by Observing Pyrene Fluorescence Losses

Black carbon (BC), the soot and char formed during incomplete combustion of fossil and biomass fuels, is ubiquitous, participates in diverse environmental processes, and has adverse effects on human health. However, uncertainty persists regarding how accurately the present measurement methods quantify total BC or even defined subportions of the BC continuum. Hence, we sought to improve this situation by developing a new, low-sample manipulation methodology that does not require any oxidative or pyrolytic treatments but rather differentiates BC from other non-BC organic carbon (OC) using its sorbent properties. The procedure, referred to as the pyrene fluorescence loss (PFL) method, infers BC concentrations in particulate organic matter (POM) by observing the decrease in fluorescence from pyrene spiked into aqueous POM suspensions. The method was first tested using diverse materials previously utilized in an international BC method intercomparison study, and then its effectiveness (e.g., sensitivity and geochemical reasonableness) was tested by applying itto sediment and seawater POM samples collected from a coastal area downwind of important BC sources. Parallel evaluation of BC, using the PFL method and CTO-375 procedure, suggested we can characterize the predominant BC in a given sample as (i) thermally recalcitrant and highly sorptive per mass (e.g., soot), (ii) thermally labile and highly sorptive per mass (e.g., char), or (iii) thermally recalcitrant but not highly sorptive (e.g., lignite coal).

Density separation of combustion-derived soot and petrogenic graphitic black carbon: Quantification and isotopic characterization

The black carbon continuum is composed of a series of carbon-rich components derived from combustion or metamorphism and characterized by contrasting environmental behavior and susceptibility to oxidation. In this work, we present a micro-scale density fractionation method that allows isolating the small quantities of soot-like and graphitic material usually found in natural samples. Organic carbon and δ13C mass balance calculations were used to quantify the relative contributions of the two fractions to thermally-stable organic matter from a series of aquatic sediments. Varying proportions of soot-like and graphitic material were found in these samples, with large variations in δ13C signatures suggesting important differences in their origin and/or dynamics in the environment.

A simplified method for the quantification of pyrogenic organic matter in grassland soils via chemical oxidation

The elucidation of the impact of pyrogenic organic carbon (PyOC) on soil ecological functions and its role within geobiochemical cycles requires a quantification that is not restricted to a certain window of the Black Carbon continuum. In the present study the method of chemical oxidation with acid dichromate was modified to allow for the determination of the whole range of PyOC in soil systems frequently subjected to prescribed fires with a fairly homogenous intensity distribution. After confirming the reproducibility of the technique, top and subsoils of Leptosols and Umbrisols from a grassland ( Campo) landscape in the Planalto region, Southern Brazil were demineralized with hydrofluoric acid and subsequently the residues were chemically oxidized. Solid-state 13C NMR spectroscopy was applied to distinguish between chemical oxidation resistant elemental C (COREC) of pyrogenic organic carbon (PyOC) and lipid components surviving the harsh treatment because of their hydrophobic properties. Correlation of the aromatic COREC content of the samples with their aromatic C content resulted in a positive correlation with R 2 = 0.74 for the topsoils and R 2 = 0.53 for the subsoils. The correlation functions allowed the development of an equation that yields in a correction factor f, which is necessary to account for the C-losses of PyOC caused by the chemical oxidation and thus for the estimation of its original contribution to the soil. For the topsoils this correction factor was comparable to that determined for a model char derived from the Campo vegetation after charring for 4 min at 350 °C. Applying this factor to Campo plant-char/soil mixtures resulted in recoveries between 93 and 125%, indicating that it should be possible to elucidate the PyOC content of soils by the determination of COREC arom and subsequent multiplication with f. In soil systems with char input of fairly consistent chemical composition, as they occur in prescribed grassland fires, f may be directly obtained from model chars produced from the respective vegetation cover.

Analysis of black carbon in sediments and soils using multi-element scanning thermal analysis (MESTA)

Analysis of black carbon (BC) is still a critical issue in carbon cycle research due to the lack of standardized methodology. This study was initiated to investigate the feasibility of quantifying BC in solid samples using a multi-element scanning thermal analysis (MESTA) method. The method determines the C and N contents of a sample, with respect to their thermal stability, over the entire organic carbon (OC)/BC continuum. There is a good separation of BC and non-BC materials in the MESTA thermograms. The tentative BC criterion is the carbonaceous material with peak carbon decomposition temperature ⩾550 °C. Charring seemed not to be a problem in the determination of BC using MESTA because the char products were not thermally stable enough to be classified as BC. Comparison of the MESTA method with the International BC Ring Trial methods ( http://www.geo.unizh.ch/phys/bc/) shows that the BC content of a Chernozem, Vertisol and the SRM 1649a urban dust are in the mid-range, while those of wood char and grass char are at the lower end of the ring trial methods. The study also reveals a significant amount of N structurally associated with the thermally stable carbonaceous material.

Can levoglucosan be used to characterize and quantify char/charcoal black carbon in environmental media?

The heterogeneous nature of pyrogenic carbon, also known as black carbon (BC), still stands in the way of comprehensive determination of the total proportion of combustion derived carbon in environmental mixtures. Char and charcoal occur mostly in the low temperature region of the BC continuum and as such are characterized using specific chemical and physical properties that set them apart from the more condensed forms of high temperature BC species (i.e., soot). This study aimed to assess the feasibility of using the molecular marker levoglucosan, exclusively produced from hemicellulose/cellulose combustion, to characterize and quantify char BC in the environment. A second objective was to compare the results from the molecular analysis with those from acid dichromate oxidation in terms of char BC characterization. First, we examined levoglucosan levels in a suite of BC materials derived from biomass burning and fossil fuel combustion, as well as non-BC materials (coal and melanoidin). The results confirm that levoglucosan is exclusively in the char BC materials, derived from biomass combustion. However, a large variability in levoglucosan yield was observed among the different char BC materials. To understand the causes of such variability, we analyzed levoglucosan in three series of laboratory-produced char samples ( n = 23) made from honey mesquite ( Prosopis glandulosa Torr.), cordgrass ( Spartina spartinae) and loblolly pine ( Pinus taeda) under controlled combustion conditions (150–1050 °C, 0.5–5 h). The results show that temperature is the most influential factor affecting levoglucosan yield in char. Combustion duration, on the other hand, had no influence on yield. Notably, levoglucosan was only detectable in low temperature char samples (150–350 °C), with maximum yield obtained from samples produced at 250 °C, regardless of plant species. Large differences in levoglucosan yield were also observed across species. This taxonomic difference could not be corrected simply on the basis of hemicellulose and cellulose content, indicating that the relationship between combustion and levoglucosan formation is a complex function of many factors. Our observations also demonstrate that levoglucosan can hardly be used quantitatively for the determination of char BC in environmental samples since such samples often represent mixtures of different chars characterized by variable levoglucosan yield. Acid dichromate oxidation, as opposed to the levoglucosan method, detected mid- to high temperature char BC (⩾350 °C) but not low temperature char (⩽ 250 °C). Our results indicate that the overlap in the analytical windows of the two methods is limited to the upper limit of the latter. The study demonstrates that levoglucosan can serve as a good qualitative indicator for the presence of char produced under low temperature conditions in soil, sediments, and ultrafine aerosols. Although levoglucosan is not a proper quantitative proxy for char BC content in the environment, this molecular marker has a unique role in the current BC methods continuum because it traces combustion material often missed with most oxidation-based methods.

Comparison of quantification methods to measure fire‐derived (black/elemental) carbon in soils and sediments using reference materials from soil, water, sediment and the atmosphere

Black carbon (BC), the product of incomplete combustion of fossil fuels and biomass (called elemental carbon (EC) in atmospheric sciences), was quantified in 12 different materials by 17 laboratories from different disciplines, using seven different methods. The materials were divided into three classes: (1) potentially interfering materials, (2) laboratory‐produced BC‐rich materials, and (3) BC‐containing environmental matrices (from soil, water, sediment, and atmosphere). This is the first comprehensive intercomparison of this type (multimethod, multilab, and multisample), focusing mainly on methods used for soil and sediment BC studies. Results for the potentially interfering materials (which by definition contained no fire‐derived organic carbon) highlighted situations where individual methods may overestimate BC concentrations. Results for the BC‐rich materials (one soot and two chars) showed that some of the methods identified most of the carbon in all three materials as BC, whereas other methods identified only soot carbon as BC. The different methods also gave widely different BC contents for the environmental matrices. However, these variations could be understood in the light of the findings for the other two groups of materials, i.e., that some methods incorrectly identify non‐BC carbon as BC, and that the detection efficiency of each technique varies across the BC continuum. We found that atmospheric BC quantification methods are not ideal for soil and sediment studies as in their methodology these incorporate the definition of BC as light‐absorbing material irrespective of its origin, leading to biases when applied to terrestrial and sedimentary materials. This study shows that any attempt to merge data generated via different methods must consider the different, operationally defined analytical windows of the BC continuum detected by each technique, as well as the limitations and potential biases of each technique. A major goal of this ring trial was to provide a basis on which to choose between the different BC quantification methods in soil and sediment studies. In this paper we summarize the advantages and disadvantages of each method. In future studies, we strongly recommend the evaluation of all methods analyzing for BC in soils and sediments against the set of BC reference materials analyzed here.

Quantification and radiocarbon source apportionment of black carbon in atmospheric aerosols using the CTO-375 method

To make progress towards linking the atmosphere and biogeosphere parts of the black carbon (BC) cycle, a chemothermal oxidation method (CTO-375), commonly applied for isolating BC from complex geomatrices such as soils, sediments and aquatic particles, was applied to investigate the BC also in atmospheric particles. Concentrations and 14C-based source apportionment of CTO-375 based BC was established for a reference aerosol (NIST RM-8785) and for wintertime aerosols collected in Stockholm and in a Swedish background area. The results were compared with thermal–optical (OC/EC) measurements. For NIST RM-8785, a good agreement was found between the BC CTO-375 concentration and the reported elemental carbon (EC) concentration measured by the “Speciation Trends Network—National Institute of Occupational Safety and Health” method (EC NIOSH) with BC CTO-375 of 0.054±0.002 g g −1 and EC NIOSH of 0.067±0.008 g g −1. In contrast, there was an average factor of ca. 20 difference between BC CTO-375 and EC NIOSH for the ambient Scandinavian wintertime aerosols, presumably reflecting a combination of BC CTO-375 isolating only the recalcitrant soot-BC portion of the BC continuum and the EC NIOSH metric inadvertently including some intrinsically non-pyrogenic organic matter. Isolation of BC CTO-375 with subsequent off-line radiocarbon analysis yielded fraction modern values (fM) for total organic carbon (TOC) of 0.93 (aerosols from a Swedish background area), and 0.58 (aerosols collected in Stockholm); whereas the fM for BC CTO-375 isolates were 1.08 (aerosols from a Swedish background area), and 0.87 (aerosols collected in Stockholm). This radiocarbon-based source apportionment suggests that contribution from biomass combustion to cold-season atmospheric BC CTO-375 in Stockholm was 70% and in the background area 88%.

Sedimentary Record of Polycyclic Aromatic Hydrocarbons in the Gulf of Trieste (Northern Adriatic Sea)

To reconstruct a history of polycyclic aromatic hydrocarbon (PAH) pollution in the Gulf of Trieste, one of the largest urbanized areas in the Adriatic Sea, we analyzed three long sediment cores collected between 1996 and 1997. Concentrations of total PAHs, the sum of 16 PAH compounds and six of their methylated analogues, in all three cores show a decrease from 600–800 ng g−1, at the surface, to levels below 250 ng g−1 in deepest layers (down to 3 m). The same trend was shown with separate representative pyrogenic PAHs (pyrene, benzofluoranthene and phenanthrene). Using Hg as a recent geochronological tracer, we observe an increasing input of PAHs since the beginning of the 20th Century and, especially, after the Second World War coinciding with increasing industrialization and urbanization of the region. This correlation is supported by PAH ratios that are indication of combustion processes and represent a marker for anthropogenic inputs. No correlation exists between PAHs and black carbon within the core profiles, indicating two different fractions of the ‘black carbon continuum’.

03/02485 Modeling for pyrolysis of solid particle: kinetics and heat transfer effects: Babu, B. V. and Chaurasia, A. S. Energy Conversion and Management, 2003, 44, (14), 2251–2275

A wide selection of thermal, chemical and optical methods have been proposed for the quantification of black carbon (BC) in environmental matrices, and the results to date differ markedly depending upon the method used. A new approach is hydropyrolysis (hypy), where pyrolysis assisted by high hydrogen pressures (150 bar) facilitates the complete reductive removal of labile organic matter, so isolating a highly stable portion of the BC continuum (defined as BChypy). Here, the potential of hypy for the isolation and quantification of BC is evaluated using the 12 reference materials from the International BC Ring Trial, comprising BC-rich samples, BC-containing environmental matrices and BC-free potentially interfering materials. By varying the hypy operating conditions, it is demonstrated that lignocellulosic, humic and other labile organic carbon material (defined as non-BChypy) is fully removed by 550 °C, with hydrogasification of the remaining BChypy not commencing until over 575 °C. The resulting plateau in sample mass and carbon loss is apparent in all of the environmental samples, facilitating BC quantification in a wide range of materials. The BChypy contents for all 12 ring trial samples fall within the range reported in the BC inter-comparison study, and systematic differences with other methods are rationalised.All methods for BC isolation, including hypy are limited by the fact that BC cannot be distinguished from extremely thermally mature organic matter; for example in high rank coals. However, the data reported here indicates that BChypy has an atomic H/C ratio of less than 0.5 and therefore comprises a chemically well-defined polyaromatic structure in terms of the average size of peri-condensed aromatic clusters of >7 rings (24 carbon atoms), that is consistent across different sample matrices. This, together with the sound underlying rationale for the reductive removal of labile organic matter, makes hypy an ideal approach for matrix independent BC quantification. The hypy results are extremely reproducible, with BChypy determinations from triplicate analyses typically within ±2% across all samples, limited mainly by the precision of the elemental analyser.