Black carbon (BC) is a distinct type of carbonaceous aerosol that has a significant impact on the environment, human health, and climate. A non-BC material coating on BC can alter the mixing state of ...the BC particles, which considerably enhances the mass absorption efficiency of BC by directing more energy toward the BC cores (lensing effect). A lot of methods have been reported for quantifying the enhancement factor (Eabs), with diverse results. However, to the best of our knowledge, a comprehensive review specific to the quantification methods for Eabs has not been systematically performed, which is unfavorable for the evaluation of obtained results and subsequent radiative forcing. In this review, quantification methods are divided into two broad categories, direct and indirect, depending on whether experimental removal of the coating layer from an aged carbonaceous particle is required. The direct methods described include thermal peeling, solvent dissolution, and optical virtual exfoliation, while the indirect methods include intercept-linear regression fitting, minimum R squared, numerical simulation, and empirical value. We summarized the principles, procedures, virtues, and limitations of the major Eabs quantification methods and analyzed the current problems in the determination of Eabs. We pointed out what breakthroughs are needed to improve or innovate Eabs quantification methods, particularly regarding the need to avoid the influence of brown carbon, develop a broadband Eabs quantification scheme, quantify the Eabs values for the emissions of low-efficiency combustions, measure the Eabs of particles in a high-humidity environment, design a real-time monitor of Eabs by a proper combination of mature techniques, and make more use of artificial intelligence for better Eabs quantification. This review deepens the understanding of Eabs quantification methods and benefits the estimation of the contribution of BC to radiative forcing using climate models.
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•Quantification methods for light absorption enhancement of BC reviewed•Methods are classified and described, with virtues and limitations recognized•A few breakthroughs wanted for quantification methods of BC absorption enhancement
The transport of black carbon (BC) to polar regions is studied using the University of Michigan IMPACT aerosol model driven by two sets of meteorological fields from the NCAR CAM5 and GFDL AM3 ...models. The sensitivity of the transport of BC to wet deposition processes is tested by varying the wet deposition in large‐scale precipitation. BC concentrations and deposition in polar regions are shown to be sensitive to both the meteorological fields and the wet deposition treatment. Using the default wet deposition, both IMPACT‐CAM5 and IMPACT‐AM3 simulate an appropriate amount of BC deposition in polar regions as compared to ice core observations. Although the seasonal cycle of BC surface air concentrations is reasonable, the concentrations are about 1∼2 orders of magnitude smaller than observations. With reduced wet deposition efficiency, the total deposition of BC increases by a factor of ∼2 to ∼3 due to more transport to the poles. The near surface BC concentrations increase even more (by a factor of ∼3 to ∼10) but are still largely underestimated especially in the north polar region. The radiative forcing from the BC deposited on snow and sea ice is also sensitive to the wet deposition treatment and the different meteorological fields. The global (Arctic) annual mean forcing is about +0.020 W m−2 (+0.11 W m−2) for IMPACT‐CAM5 and +0.022 W m−2 (+0.13W m−2) for IMPACT‐AM3.
Key Points
BC in polar regions are sensitive to meteorological fields and wet depositions
Black carbon snow forcing is estimated to be +0.020 ‐+0.022 W m‐2
Discrepancy of BC concentration and deposition may be related to BC lifetime
The conversion of food waste and sludge into biogas via anaerobic digestion technology is gaining attention in recent years, which plays a significant role in waste valorization into bioenergy and ...promotes environmental sustainability. Biochar is a carbonaceous material produced via thermochemical conversion of biomass waste, and tailoring biochar for diverse environmental applications adheres to the principle of circular economy. The emerging application of biochar as an additive in the anaerobic digestion of food waste and sludge has been intensively investigated in the last few years. However, a comprehensive understanding of multifunctional roles of biochar and its mechanisms in the production of biogas via miscellaneous/complex anaerobic digestion process is yet to be attained. This review scrutinizes the key roles of biochar as an additive and emphasizes the influences of biochar characteristics on the anaerobic digestion processes and their capability to address the foremost challenges. This review also evaluates the techno-economic and environmental impacts of biochar synthesis and its emerging application for biogas production via anaerobic digestion to make the integrated process more economical and environmentally sustainable, and identifies challenges and prospects for future studies.
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•Biochar manifests tunable physicochemical properties for diverse applications.•Biochar facilitates efficient anaerobic digestion (AD) of food waste and sludge.•Microbial functions and enzymatic activity can be enhanced by biochar addition.•A closed-loop material flow can be realized by integrating AD and pyrolysis.
The mass concentration of atmospheric particulate matter (PM) has been continuously decreasing in the Beijing-Tianjin-Hebei region. However, health endpoints do not exhibit a linear correlation with ...PM mass concentrations. Thus, it is urgent to clarify the prior toxicological components of PM to further improve air quality. In this study, we analyzed the long-term oxidative potential (OP) of water-soluble PM2.5, which is generally considered more effective in assessing hazardous exposure to PM in Beijing from 2018 to 2022 based on the dithiothreitol assay and identified the crucial drivers of the OP of PM2.5 based on online monitoring of air pollutants, receptor model, and random forest (RF) model. Our results indicate that dust, traffic, and biomass combustion are the main sources of the OP of PM2.5 in Beijing. The complex interactions of dust particles, black carbon, and gaseous pollutants (nitrogen dioxide and sulfur dioxide) are the main factors driving the OP evolution, in particular, leading to the abnormal rise of OP in Beijing in 2022. Our data shows that a higher OP is observed in winter and spring compared to summer and autumn. The diurnal variation of the OP is characterized by a declining trend from 0:00 to 14:00 and an increasing trend from 14:00 to 23:00. The spatial variation in OP of PM2.5 was observed as the OP in Beijing is lower than that in Shijiazhuang, while it is higher than that in Zhenjiang and Haikou, which is primarily influenced by the distribution of black carbon. Our results are of significance in identifying the key drivers influencing the OP of PM2.5 and provide new insights for advancing air quality improvement efforts with a focus on safeguarding human health in Beijing.
There is global interest in understanding the prospects for biochar application to agricultural soils. If biochar enhances the availability of nitrogen (N) and phosphorus (P) to crops, this could be ...pivotal in reducing N and P fertilizer inputs to agricultural soils. This review evaluates the soil biochemical cycling of N and P as influenced by biochars with diverse characteristics, and describes the consequences for plant nutrition with respect to the N use efficiency (NUE) and P use efficiency (PUE) of crops grown in biochar-amended soils. Fundamentally, biochar can alter microbial-mediated reactions in the soil N and P cycles, i.e. N2 fixation, mineralization of N and P, nitrification, ammonia volatilization and denitrification. As well, biochar provides reactive surfaces where N and P ions are retained in soil microbial biomass and in exchange sites, both of which modulate N and P availability to crops. Distinctions must be made between biochars derived from manure- and crop residue-based feedstocks versus biochars derived from ligno-cellulosic feedstock, as well as biochars produced at a lower production temperature (<400 °C) versus biochars generated at a higher production temperature (≥600 °C). These factors determine the nutrient retention capacity of biochars when they are applied to soil. For example, low bioavailable N and P concentrations are expected when coarse-textured soil is amended with biochar having a high surface area, necessitating fertilizer application to avoid N and P deficiencies in the crop. Since the biochemical cycling of N and P in biochar-amended soil is affected strongly by biochar × soil interactions, detailed assessment of biochar-induced changes in soil physico-chemical properties and biological processes may improve predictions of how diverse biochars will affect soil fertility and crop nutrition under site-specific conditions.
•Biochar alters soil physico-chemical and biological properties, and nutrient cycling.•Soil N and P dynamics are a function of interactions between biochar type and soil.•N and P cycling is modulated by biochar-induced changes in microbial processes.•Biochar-induced N and P immobilization can be overcome by applying fertilizer.•There is a research gap regarding nutrient use efficiency in biochar-amended soil.
We examine long‐term trends in the near‐surface black carbon mass concentration, using multiyear primary data obtained from a dense network (ARFINET) of observatories over the Indian region. We ...report for the first time the statistically significant decreasing trend in black carbon mass concentration, based on primary data from this region, at an average rate of ~242 ± 53 ng · m−3 · year−1 during the period 2007–2016. This finding contrasts with the generally increasing trend in the columnar aerosol optical depth, reported earlier, and the steadily increasing trend in anthropogenic activities over this region. The roles of different possible mechanisms, including possible changes in the vertical redistribution of aerosols, are discussed. Over the period 2007–2015, a significant though weak, increasing trend is seen in the contribution from aerosols above 1 km to the columnar aerosol optical depth. These observations imply possible long‐term climate consequences.
Key Points
We report the first time regional synthesis of black carbon aerosols over the Indian region using primary data
The study revealed surprising observation of decreasing trend in the near surface black carbon aerosol concentration
We found an increasing trend in contribution from free tropospheric aerosols to the columnar aerosol optical depth
Soil degradation has become an emerging global problem limiting sustainable upland crop production. Soil erosion, soil acidity, low fertility, inorganic/organic contamination, and salinization ...challenge food security and lead to severe economic constraints. Therefore, a new research agenda to develop cost-beneficial amendments for improving upland soil quality and productivity is urgently required. Biochar has been used in recent years to mitigate the problems mentioned above. Application of biochar improves the upland soil quality through significant changes in soil physicochemical and biological properties, thereby substantially increasing crop yield. This review article aims to discuss the effects of biochar on upland soil quality and productivity based on biochar-soil interactions. The yield of various upland crops can be enhanced by biochar-induced increases of nutrient availability and topsoil retention/recovery. Furthermore, biochar can assist in controlling unsuitable soil acidity/alkalinity/salinity and remediating a contaminated soil while increasing the retention of soil organic carbon, water content, and thereby high crop yield. Biochar is strongly recommended as one of the best management practices to meet the challenges of upland agriculture. However, the properties of biochar and soil type should be considered carefully prior to application.
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•Potential uses of biochar to address the emerging global problem of soil degradation are reviewed.•Biochar-soil interactions trigger beneficial changes in soil physical, chemical, and biological characteristics.•Biochar is a cost-effective amendment for remediating upland soil quality and improving crop productivity.•Selection of biochar must match substrate type and production conditions to desirable soil attributes and intended uses.
Black carbon (BC) is ubiquitous in the environment and is a significant component of the refractory carbon pool. However, its sources, biogeochemical processes, and environmental residence times are ...poorly understood. One important reason is that the technical protocols for isolating/analyzing BC vary across different matrices, thereby bringing inconsistency among studies on BC in different environment media. Benzene polycarboxylic acids (BPCA), produced by nitric acid oxidation of the condensed aromatic structure that is common in BC and BC-like substances, has been proven to be a useful molecular proxy for tracking BC in the Earth's surface. Here, we introduce a new technical approach for the compound-specific dual-carbon isotope (δ13C and Δ14C) analysis of BPCA. The BPCA compounds are isolated using preparative liquid chromatography, in which trifluoroacetic acid is used in the mobile phase instead of phosphoric acid. This allows complete removal of solvent from the isolated BPCA fraction, so that conversion of BPCA isolates into CO2 can be done by conventional oxidation methods for off-line Δ14C analysis with accelerator mass spectrometry. Liquid chromatography (void column)-stable carbon isotope ratio mass spectrometry is employed to measure δ13C of the isolated BPCA, leaving as much BPCA carbon amount as possible for 14C analysis. Blockage of oxidation chamber due to incomplete oxidation of other organic acids in the samples is avoided thanks to preliminary isolation of BPCA. We tested the approach by applying it to solid and dissolved BC species in a suite of environmental reference materials, including maize char, coal, riverine natural organic matter (NOM 2R101N), marine sediment (SRM 1941b), urban dust (SRM 1649b), and coke-polluted soils. We assessed the offsets of BPCA-δ13C and BPCA-Δ14C values caused by procedural carbon contaminations to correct measured carbon isotopic values. Paired δ13C-Δ14C data of individual BPCA were plotted to validate and demonstrate the ability of this dual carbon isotope technique in tracking BC across different environmental matrices. We observed slightly different δ13C-Δ14C signatures among individual BPCA, indicating that the less condensed BC may have younger apparent radiocarbon ages.
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•We outline a new approach for compound-specific δ13C-Δ14C analysis of BPCA.•Mobile phases of BPCA fractions isolated with HPLC are totally removed.•Validation using BC reference materials of various environmental media.
Biochar is an emerging low-cost sorbent used for removing trace metals from water. In this study, we evaluated the removal potential of aqueous hexavalent chromium (Cr(VI)) by biochars produced from ...soybean (Glycinemax L.) and burcucumber (Sicyos angulatus L.) residues. The highest Cr(VI) removal from solution occurred at low pH values (pH2–5), and adsorption decreased approximately tenfold when the pH increased from 2 to 10. Synchrotron-based X-ray absorption spectroscopy (XAS) investigations showed that Cr(VI) species were reduced to trivalent chromium (Cr(III)) at the biochar surface following Cr(VI) adsorption. Linear combination fitting (LCF) of X-ray absorption near edge structure (XANES) data indicated that approximately 90% of the total Cr(VI) (962μM) was reduced to Cr(III). Extended X-ray absorption fine structure (EXAFS) fitting results yielded interatomic chromium (CrCr) distances consistent with the formation of Cr(III) precipitates as Cr(OH)3. Trivalent chromium is far less soluble than Cr(VI) and typically precipitates as amorphous Cr(III) solids. Thus, biochars produced by soybean and burcucumber residues are a promising technique for both adsorbing and reductively immobilizing Cr(VI) from aqueous solutions.
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•Removal potential of aqueous Cr(VI) by biochar was evaluated.•The highest Cr(VI) removal occurred at low pH values.•Cr(VI) species can be reduced to Cr(III) at the biochar surface.•Biochar properties determine the coordination environment of Cr(III) products.
The use of biochar has been suggested as a means of remediating contaminated soil and water. The practical applications of conventional biochar for contaminant immobilization and removal however need ...further improvements. Hence, recent attention has focused on modification of biochar with novel structures and surface properties in order to improve its remediation efficacy and environmental benefits. Engineered/designer biochars are commonly used terms to indicate application-oriented, outcome-based biochar modification or synthesis. In recent years, biochar modifications involving various methods such as, acid treatment, base treatment, amination, surfactant modification, impregnation of mineral sorbents, steam activation and magnetic modification have been widely studied. This review summarizes and evaluates biochar modification methods, corresponding mechanisms, and their benefits for contaminant management in soil and water. Applicability and performance of modification methods depend on the type of contaminants (i.e., inorganic/organic, anionic/cationic, hydrophilic/hydrophobic, polar/non-polar), environmental conditions, remediation goals, and land use purpose. In general, modification to produce engineered/designer biochar is likely to enhance the sorption capacity of biochar and its potential applications for environmental remediation.
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•Recent developments of engineered biochar for contaminant removal are reviewed.•Chemical, physical, impregnation, and magnetic approaches improve applicability.•Immobilization mechanisms of organic/inorganic contaminants are evaluated.•Outcome-based biochar modifications can enhance environmental remediation.
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