B23D-0474
Ageing of black carbon along a temperature gradient
Black carbon (BC) is regarded as a chemically and biologically stable form of carbon and the changes of BC properties in nature are generally assumed to be minute. However, more and more observations have argued the inertness of BC. The objectives of this study were to characterize the changes of BC properties through ageing processes and to identify if these changes associated with the incubation temperature and time. Our results showed that the ageing of BC could be undertaken over a temperature range from -22C to 70C within a short time of 12 months. The major changes of BC properties through ageing were found in elemental composition, surface chemistry, and adsorption properties. The aged BCs were shown to have higher oxygen concentration, surface acidity, and negative surface charge but lower carbon concentration, pH, surface basicity, point of zero net charge, and also a less adsorption capacity to hydroquinone, an allelopathic compound, than the fresh BC. These ageing processes of BC were affected by the temperature and time, in which the higher temperature and longer time were crucial in enhancing BC ageing. Our results from a wide temperature range suggest that the ageing of BC is like to occur in any terrestrial regime and the changes of BC properties through ageing should not be overlooked.
B23D-0475
Climate-Related Variations in Black Carbon Accumulation in Chesapeake Bay Holocene Sediments
A sediment core collected in the mesohaline portion of Chesapeake Bay indicates periods of increased delivery of refractory black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs). Their geochemical signature suggests the enriched BC concentrations were generated by biomass combustion during four centennial-scale dry periods, as indicated by the Palmer Drought Severity Index (PDSI), beginning in the late Medieval Warm Period of 1100 CE. Geochemical evidence also suggests that the BC was produced during drought-induced wildfires that were spatially extensive and the combusted biomass contained relatively greater proportions of C4 vegetation. In contrast, wetter periods were associated with fewer regional fires and increased authochonous non-BC organic matter influx into the Bay, due, perhaps, to increased nutrient delivery from enhanced soil erosion and runoff. An overall increase in both BC and non-BC organic matter deposition over the past millennium was observed and may be caused by enhanced fire/flood cycles resulting from higher amplitude climatic fluctuations during this period. The finding that carbon sequestration in the coastal zone is related to climate fluctuations at both centennial and millennial scales through fire occurrence and nutrient delivery has implications for past and future climate predictions. Drought-induced fires might represent a negative climate feedback.
B23D-0476
Reconstructing Holocene Fire History for Northern Israel: The Role of Climate and Human Activity
We present a late-Holocene record of fire frequency and climate for the Galilee region of Israel using microcharcoal, black carbon and sedimentary geochemical proxies from deep-water sediments of Lake Kinneret (the Sea of Galilee). Long-term fire histories provide valuable insight into the effect of variations in climate, ecology and human influence on past fire regime, which in turn provides a fundamental background for understanding possible implications of future climate change on wildfires. The goal of this study is to compare the fire record from this lake (the first long-term fire record for the region) to records of local and regional climate variability and to historical records of local human activity in order to determine which factors exert the greatest control over changes in fire frequency for this area. Comparison of fire proxies (microcharcoal and black carbon abundance) to climate and productivity proxies from the same core (organic and inorganic matter abundance and their isotopes) shows that periods of low fire frequency often correlate with periods of low sediment calcium carbonate content, low carbonate isotopic values (d13C, d18O), low organic matter content (C and N), and high organic nitrogen isotopic values (d15N). Charcoal and black carbon show significant variability over the 2.8m core, with a prolonged drop in fire frequency at 1.50-1.85 m, which may correspond to the period ~1800-2200 years before present, documented by other local and regional records of climate as one of the wettest periods in the late Holocene, and also the period of greatest human habitation in the region before the present.
B23D-0477
Black carbon in Central California: soil carbon and air quality implications
Black carbon (BC) plays a significant role in the carbon cycle, simultaneously influencing the quality of air from local to regional scales from its point of origin. We are investigating these influences with respect to BC recently produced in the Central Valley and Sierra Nevada Forest area of California. Surface biomass, charred matter and soil (0-5 cm) were collected after prescribed fires in Yosemite National Park (YNP) locations along an elevational gradient ranging from 1148 m to 1992 m. Surface soils and aerosols from a protected (non-burnt) grassland in Merced (central valley) were also collected. Soil organic carbon (SOC) concentrations in burnt sites were analyzed and compared with concentrations in adjacent unburnt soils (controls). The SOC concentrations ranged from 3 to 15% in the control soils and 2 to 12% in post-burn soils. Initial results show a lack of significant change in surface SOC concentration from prescribed fires in the YNP forest sites. The relative contribution of fossil fuel combustion versus biomass combustion on soil deposited aerosol BC (soot) was determined using radiocarbon analysis with accelerator mass spectrometry. Initial findings show an increase in the contribution of fossil fuel combustion to soot BC with decreasing elevation in YNP, with little difference between burnt and recently unburnt sites. The BET surface area of BC from the field samples will also be analyzed and compared with BC produced in the lab from field-collected biomass. Bulk carbon composition and an assessment of the relative percentage BC present in the samples will be conducted with 13-C NMR analysis. This will help in the establishment of a relationship between black carbon and total carbon in central California. In this poster, will be presenting some of our initial findings and their implications for air quality and carbon budget balance in central California. The effects of prescribed fires on soil carbon and black carbon properties will also be discussed.
B23D-0478
Black Carbon Concentrations in Urban and Rural Arid-Land Soils
This study examines black carbon (BC) in soils from central Arizona. Black carbon (BC) is the product of incomplete combustion of biomass and fossil fuel. It has a wide range of physical structures from slightly charred biomass to soot carbon, that vary in size from millimeter-scale to submicrometer-scale, respectively. BC has been shown to make up a large portion (up to 50 %) of the soil organic carbon pool. However, many uncertainties exist in global and regional BC budgets that are directly related to the wide variety of experimental techniques used to measure BC. Although traditionally thought to be quite refractory, it is now known that more BC is produced than is stored in sinks annually. Because of this imbalance, a more dynamic role for BC in the environment must be considered. Very little is currently known about BC reactivity in soil. Examining soils with both fossil fuel derived and biomass derived BC inputs can reveal information about BC functionality and aid in the understanding of it's role in earth's reactive carbon pool. Soil samples were collected as a part of the 200-Point Survey conducted by the Central Arizona - Phoenix Long-Term Ecological Research (CAP-LTER) project. Soil samples from a range of sites around the Phoenix-metro area were classified by land cover and land use. Total carbon, weight % organic carbon, and weight % inorganic carbon were measured at each site. Forty-eight survey points ranging from rural desert soils to urban soils were sub-sampled and analyzed for BC concentration. BC was isolated from the bulk soil carbon using a chemo-thermal oxidation technique commonly known as CTO375. Concentrations of BC were measured using an elemental analyzer coupled to an isotope ratio mass spectrometer. Our results show that BC makes up from 0.01 to 0.78 % of the total weight of soil. An amount that corresponds to between 1.65 and 62.86 % of the organic carbon pool. This indicates that a significant portion of the organic carbon in central Arizona soils can be defined as black carbon. Mapping these BC contents across the Phoenix metropolitan area reveals a general pattern with higher BC contents in soils from urban locations and lower BC contents in soils from the urban fringe and rural areas. The highest BC contents are associated with major freeways and the pattern suggests that within the urban core, fossil fuel burning contributes a significant source of BC.
B23D-0479
Dissolved Black Carbon in the Southern Ocean along CLIVAR section I6S
Thermogenic matter ("black carbon", BC) is abundant in the environment. BC is produced during catagenesis in earth's crust and is also a residue of fossil fuel and biomass burning. Because of its refractory character, BC accumulates in soils and sediments and sequesters carbon from active cycles. Previous studies found indications that BC might be a significant component also in marine dissolved organic matter (DOM). However, the available information on black carbon in DOM is extremely rare up to now. The objective of this study is to quantify BC in marine DOM and identify the source and dynamics of dissolved BC for a major oceanic region. Detailed depth profiles were sampled along 30º E from South Africa to Antarctica at 1º intervals on CLIVAR section I6S. Dissolved BC was isolated from approximately 250 seawater samples via a new solid phase extraction method. Fused aromatic ring systems as a molecular tracer for BC were quantified in these samples. For this purpose, the samples were oxidized with nitric acid and the reaction products of fused ring systems analyzed as benzene-polycarboxylic acids with HPLC. BC concentrations were very stable throughout the water column and along the North-South section, ranging between 500 and 700 nM BC. The molecular composition of benzene-polycarboxylic acids indicates a relatively small number of fused aromatic rings per molecule. Similar structures were observed preciously in riverine and also petroleum-derived DOM. The homogenous distribution of BC in all water masses indicates conservative behavior of BC in the ocean, and turnover rates which are far longer than oceanic turnover rates. The stable character of dissolved BC and its abundance in the ocean has major implications for our understanding of global biogeochemical cycles.
B23D-0480
Understanding the Impact of Charcoal Inputs to Soils and Sediments on Conventional Geochemical Markers
Chars/charcoals are solid combustion residues derived from biomass burning. They represent one of the major classes in the pyrogenic organic residues, the so-called black carbon (BC), and have highly heterogeneous nature due to the highly variable combustion conditions during biomass burning. More and more attention has been given to characterize and quantify the inputs of charcoals to different environmental compartments since they also share the common features of BC, such as recalcitrant nature and strong sorption capacity on hydrophobic organic pollutants. Moreover, such inputs also imply the thermal alteration of terrestrial organic matter, as well as corresponding biomarkers such as lignin. Lignin is considered to be among the best-preserved components of vascular plants after deposition, due to its relative stability on biodegradation. This macropolymer is an important contributor to soil organic matter (SOM) and its presence in aquatic environments helps trace the input of terrigenous organic matter to such systems. The yields and specific ratios of lignin oxidation products (LOP) from alkaline cupric oxide (CuO) oxidation method have been extensively used to identify the structure of plant lignin and estimate inputs of plant carbon to soils and aquatic systems, as well as evaluate the diagenetic status of lignin. Although the fate of lignin under microbiological and photochemical degradation pathways have been thoroughly addressed in the literature, studies assessing the impact of thermal degradation on lignin structure and signature are scarce. In the present study, we used three suites of lab-made chars (honey mesquite, cordgrass, and loblolly pine) to study the impact of combustion on lignin and their commonly used parameters. Our results show that combustion can greatly decrease the yields of the eight major lignin phenols (vanillyl, syringyl, and cinnamyl phenols) with no lignin phenols detected in any synthetic char produced at ≥ 400°C. With increasing combustion temperature, internal phenol ratios (S/V and C/V) show a two-stage change with an initial increase at low temperatures followed by marked and rapid decreases when temperatures reach 200- 250°C. The acid/aldehyde ratios of vanillyl phenols ((Ad/Al)v) and syringyl phenols ((Ad/Al)s) all increase with increasing combustion temperature and duration and reach a maximum values at 300- 350°C, regardless plant species. The highly elevated acid/aldehyde ratios reached in some cases exceed the reported values of humic and fulvic acids extracted from soils and sediments. We applied these empirical data in mixing models to estimate the potential effects of charcoal inputs on the observed lignin signatures in environmental mixtures. The shifts in lignin signatures are strongly influenced both by the characteristics of the charcoal incorporated and the proportion of charcoal in the mixture. We validated our observations with two sets of environmental samples, including soils from control burning sites, and a sediment core from a wetland with evidence of charcoal inputs, showing that the presences of charcoals do alter the observed lignin signals in these samples. Such a thermal "interference" on lignin parameters should thus be considered in environmental mixtures with recognized char input.
B23D-0481
Phytotoxicity and Plant Productivity Analysis of Tar-Enriched Biochars
Biochar is one of the three by-products obtained by the pyrolysis of organic material, the other two being syngas and bio-oil. The pyrolysis of biomass has generated a great amount of interest in recent years as all three by-products can be put toward beneficial uses. As part of a larger project designed to evaluate the hydrologic impact of biochar soil amendment, we generated a biochar through fast pyrolysis (less than 2 minutes) of sorghum stock at 600°C. In the initial biochar production run, the char bin was not purged with nitrogen. This inadvertent change in pyrolysis conditions produced a fast-pyrolysis biochar enriched with tars. We chose not to discard this batch, however, and instead used it to test the impact of tar-enriched biochars on plants. A suite of phytotoxicity tests were run to assess the effects of tar-rich biochar on plant germination and plant productivity. We designed the experiment to test for negative effects, using an organic carbon and nutrient-rich, greenhouse- optimized potting medium instead of soil. We used Black Seeded Simpson lettuce (Lactuca sativa) as the test organism. We found that even when tars are present within biochar, biochar amendment up to 10% by weight caused increased lettuce germination rates and increased biomass productivity. In this presentation, we will report the statistical significance of our germination and biomass data, as well as present preliminary data on how biochar amendment affects soil hydrologic properties.
B23D-0482
Forest Fire Derived Black Carbon in the Adirondack Mountains, NY, ~1745 to 1850 A.D.
Abstract Black carbon (BC), a product of incomplete combustion, is ubiquitously present in our environment. The term BC and BC (elemental carbon) are often synonymously used. It absorbs solar radiation and causes heating of the atmosphere. Its presence in the atmosphere as fine particles has been linked to cardiac and pulmonary disease. It constitutes a significant portion of the organic matter. Long-term BC data, either in atmosphere or sediments is sparse. The sources of BC are forest fires, biomass burning, coal-, gasoline-, and diesel-combustion. Contributions from these sources have drastically changed over the last three centuries. Before ~1880, little fossil fuel was used in the United States. Hence BC was produced almost entirely from the biomass burning, either as a source of heat or forest fires. Contribution from forest fires must have dominated in the United States before human population reached a significant level. Lake sediments can be used to quantify BC emissions backward in time. Husain et al [JGR 113, D13102, doi:10.1029/2007JD009398, 2008] developed a new technique to calibrate the deposition of BC in to lake sediments, and used the BC measurements in individual sediment samples to determine atmospheric BC concentrations from ~1850 to 2005. In this work we have attempted to extend the measurements back to ~1745. Bottom sediment cores were collected from West Pine Pond (44°20'N, 74°25'W) using gravity coring, sliced into 1.25 or 2.5 cm sections, and freeze dried. The ages or the time of deposition of each section was determined using 210Pb dating technique. The 55- cm long core represented about 260 years or the 1745 to 2005 period. BC was separated from the sediments using a technique described by Husain et al [2008], and concentrations determined using the thermal optical method. The BC concentrations ranged from 0.2 to 3 mg g-1 dry weight of the sediment. The BC concentrations increased sharply around 1890 to 1902, reaching a level of 1.27 mg g-1, or about five times higher than that observed in 1854- 1865. Preliminary data shows only a small variation in the concentration from ~1745 to ~1845. So the level observed during the later period could be used to deduce an upper limit for BC concentrations resulting from forest fires in the United States. It should be recognized that these are long term averages and hence subject to large year to year variations. The appearance of anthropogenic BC component as a major source appears consistent with the population growth in the Eastern US. For example, the population of New York City in 1700, 1790, 1839, 1850, 1870, 1910 was 4937, 33131, 197112, 515547, 942292, 4766883, respectively. It is likely that population growth in the Eastern US followed similar or slower growth. We believe that a more detailed analysis of the lake sediment cores and our technique to determine atmospheric concentrations from sediment measurements can delineate contributions from various sources of BC over the last ~260 years.
B23D-0483
Abiotic and Biotic Remineralization Rates of a Variety of Laboratory-Produced Black Carbons (Biochars)
Black carbon (BC) has generally been regarded as biologically and chemically inert due to its chemical structure and longevity in the geosphere. However, considering its estimated production rate, it must turnover at significant rates. While recent studies have recorded measurable degradation rates in short-term microbial incubations, little is known as to the range of degradation rates that occur with different BC forms, or the chemical and physical variables that control rates of microbial utilization. We present the results of microbial and abiotic incubations of a variety of biochars produced from a range of biomass types (woods and grasses) and under a range of controlled (temperature and atmosphere) conditions. Over six months, specific remineralization rates stabilized at 10-30 ug C/g char-day for abiotic and 20-65 ug C/g char-day for microbial incubations. Assuming first-order exponential decay and steady state conditions, these rates would represent BC half-lives ranging from 600 to 4000 y. In general, biochar produced in the presence of oxygen had the greatest remineralization rates and was lowest for those produced without oxygen and at the highest temperatures. Overall, biochar derived from grasses were remineralized at greater rates than those from wood biomass and there was no dependence upon particle size. The influence of labile organic matter additions on BC degradation (priming) will also be discussed.
B23D-0484
Implication of Coal Tar and Asphalt on Black Carbon Quantification in Urban Watersheds
Sorption to black carbon (BC) is an important process that controls the transport and fate of persistent organic pollutants in aquatic environments. Efforts have been made to measure BC in different environmental matrices including aerosols, soils, and sediments; however, few studies have attempted to evaluate BC in dust from urban streets or parking lots, which can be an important BC source in urban lake sediments. Methods to quantify BC in soils and sediments usually involve the removal of non-BC carbonaceous materials with chemical and/or thermal oxidation followed by elemental analysis. The presence of coal tar pitch and asphalt in urban pavement dust is hypothesized to potentially result in an overestimate of BC. The primary objectives of this research are to identify the distribution of BC in a small urban watershed and to investigate the potential interference from coal tar and asphalt on BC quantification by method intercomparison. Samples were collected from the Lake Como watershed in Fort Worth, Texas. They include dust from coal-tar-sealed and unsealed parking lots and residential streets, soils from residential and commercial areas, stream bed sediments, and lake sediment cores. After density separation, samples were subjected to sequential chemical treatments and thermal treatment. Commercial coal tar pitch and asphalt products were subjected to these same treatments for comparison. BC contents quantified with chemical treatment and chemo-thermal oxidation at 375°C (CTO-375) were compared with those characterized using organic petrography. The chemical treatment predicted greater BC contents than organic petrography in all samples, and the greatest difference is in the sealed parking lot dust. CTO-375 method also predicted greater BC content in this sample than organic petrography. Commercial coal tar pitch was resistant to thermal oxidation and both coal tar pitch and asphalt were resistant to the chemical treatment. These results indicate that chemical and thermal treatments can overestimate BC contents due to the chemical and thermal resistance of these materials. We recommend that interference from coal tar pitch and asphalt be considered when chemical or thermal oxidation methods are applied to quantify BC in urban environments, where urban runoff from parking lots and paved streets plays an important source role.
B23D-0485
Radiocarbon values of black carbon using the benzene polycarboxylic acid method
Black carbon (BC) has been studied extensively, yet many questions remain about its degradation in the environment. Analytical techniques that quantify and characterize BC cannot provide estimates of the turn over time. We have modified the benzene polycarboxylic acid (BPCA) method for BC quantification and radiocarbon (14C) analysis. The BPCA method chemically oxidizes BC into BPCAs. The structure of BC determines the relative distribution of BPCA formed, with chars forming less substituted BPCAs than soots. Radiocarbon analysis of BPCAs may shed light on BC cycling and transformation. We will discuss our progress and radiocarbon values of BC materials used in the recent BC ring trial (Hammes et al, Global Biogeochemical Cycles, 2007).
B23D-0486
Using Sediment Records to Reconstruct Historical Inputs Combustion-Derived Contaminants to Urban Airsheds/Watersheds: A Case Study From the Puget Sound
Urban centers are major sources of combustion-derived particulate matter (e.g. black carbon (BC), polycyclic aromatic hydrocarbons (PAH), anhydrosugars) and volatile organic compounds to the atmosphere. Evidence is mounting that atmospheric emissions from combustion sources remain major contributors to air pollution of urban systems. For example, recent historical reconstructions of depositional fluxes for pyrogenic PAHs close to urban systems have shown an unanticipated reversal in the trends of decreasing emissions initiated during the mid-20th Century. Here we compare a series of historical reconstructions of combustion emission in urban and rural airsheds over the last century using sedimentary records. A complex suite of combustion proxies (BC, PAHs, anhydrosugars, stable lead concentrations and isotope signatures) assisted in elucidating major changes in the type of atmospheric aerosols originating from specific processes (i.e. biomass burning vs. fossil fuel combustion) or fuel sources (wood vs. coal vs. oil). In all studied locations, coal continues to be a major source of combustion-derived aerosols since the early 20th Century. Recently, however, oil and biomass combustion have become substantial additional sources of atmospheric contamination. In the Puget Sound basin, along the Pacific Northwest region of the U.S., rural locations not impacted by direct point sources of contamination have helped assess the influence of catalytic converters on concentrations of oil-derived PAH and lead inputs since the early 1970s. Although atmospheric deposition of lead has continued to drop since the introduction of catalytic converters and ban on leaded gasoline, PAH inputs have "rebounded" in the last decade. A similar steady and recent rise in PAH accumulations in urban systems has been ascribed to continued urban sprawl and increasing vehicular traffic. In the U.S., automotive emissions, whether from gasoline or diesel combustion, are becoming a major source of combustion-derived PM and BC to the atmosphere and have started to replace coal as the major source in some surficial reservoirs. This increased urban influence of gasoline and diesel combustion on BC emissions was also observed in Europe both from model estimates as well as from measured fluxes in recent lake sediments.