Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption; influence on liquid, mixed phase, and ice clouds; and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr−1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models and should be increased by a factor of almost 3. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m−2 with 90% uncertainty bounds of (+0.08, +1.27) W m−2. Total direct forcing by all black carbon sources, without subtracting the preindustrial background, is estimated as +0.88 (+0.17, +1.48) W m−2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m−2 with 90% uncertainty bounds of +0.17 to +2.1 W m−2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m−2, is the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of short-lived co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil fuel and biofuel) have an industrial-era climate forcing of +0.22 (−0.50 to +1.08) W m−2 during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all short-lived emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all short-lived species from black-carbon-rich sources becomes slightly negative (−0.06 W m−2 with 90% uncertainty bounds of −1.45 to +1.29 W m−2). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.

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Bounding the role of black carbon in the climate system: A scientific assessment

National Institute of Standards and Technology における超伝導研究及び生活

Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.

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Fire in the Earth System

Char black carbon (BC), the solid residue of incomplete combustion, is continuously being added to soils and sediments due to natural vegetation fires, anthropogenic pollution, and new strategies for carbon sequestration (“biochar”). Here we present a molecular-level assessment of the physical organization and chemical complexity of biomass-derived chars and, specifically, that of aromatic carbon in char structures. Brunauer−Emmett−Teller (BET)−N2 surface area (SA), X-ray diffraction (XRD), synchrotron-based near-edge X-ray absorption fine structure (NEXAFS), and Fourier transform infrared (FT-IR) spectroscopy are used to show how two plant materials (wood and grass) undergo analogous but quantitatively different physical−chemical transitions as charring temperature increases from 100 to 700 °C. These changes suggest the existence of four distinct categories of char consisting of a unique mixture of chemical phases and physical states: (i) in transition chars, the crystalline character of the precursor ma...

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Dynamic molecular structure of plant biomass-derived black carbon (biochar)

Agricultural activities and soils release greenhouse gases, and additional emissions occur in the conversion of land from other uses. Unlike natural lands, active management offers the possibility to increase terrestrial stores of carbon in various forms in soil. The potential to sequester carbon as thermally stabilized (charred) biomass using existing organic resource is estimated to be at least 1 Gt yr − 1 and “biochar,” defined by its useful application to soil, is expected to provide a benefit from enduring physical and chemical properties. Studies of charcoal tend to suggest stability in the order of 1000 years in the natural environment, and various analytical techniques inform quantification and an understanding of turnover processes. Other types of biochar, such as those produced under zero-oxygen conditions have been studied less, but costs associated with logistics and opportunity costs from diversion from energy or an active form in soil demand certainty and predictability of the agronomic return, especially until eligibility for carbon credits has been established. The mechanisms of biochar function in soil, which appear to be sensitive to the conditions prevailing during its formation or manufacture, are also affected by the material from which it is produced. Proposed mechanisms and some experimental evidence point to added environmental function in the mitigation of diffuse pollution and emissions of trace gases from soil; precluding the possibility of contaminants accumulating in soil from the incorporation of biochar is important to ensure safety and regulatory compliance.

A review of biochar and its use and function in soil

. Concepts were developed to establish relationships between the stable carbon
isotope ratios of nitrophenols in the atmosphere and the photochemical processing
of their precursors, light aromatic volatile organic compounds. These concepts
were based on the assumption that nitrophenols are formed dominantly from the
photo-oxidation of aromatic volatile organic compounds (VOCs). A mass balance model as well as various
scenarios based on the proposed mechanism of nitrophenol formation were
formulated and applied to derive the time-integrated exposure of the
precursors to processing by OH radicals ( ∫ [OH]d t ) from ambient
observations made between 2009 and 2012 in Toronto, Canada. The mechanistic
model included the possibility of isotopic fractionation during intermediate
steps, rather than only during the initial reaction step. This model takes
kinetic isotope effects for the reaction of the precursor VOC with
the hydroxyl radical and their respective rate constants into account, as well as carbon
isotope ratio source signatures. While many of these values are known, there
are some, such as the kinetic isotope effects of reactions of first- and
second-generation products, which are unknown. These values were predicted in
this study based on basic principles and published laboratory measurements of kinetic
carbon isotope effects and were applied to the mechanistic model. Due to the
uncertainty of the estimates based on general principles, three scenarios were
used with different values for isotope effects that were not known from
laboratory studies. Comparison of the dependence between nitrophenol carbon
isotope ratios and ∫ [OH]d t with published results of laboratory
studies and ambient observations was used to narrow the range of plausible
scenarios for the mechanistic model. The results also suggests that mass-balance-based
models do not adequately describe the dependence between
nitrophenol carbon isotope ratios and ∫ [OH]d t .

/pdf/dependence-between-the-photochemical-age-of-light-aromatic-21iuejt03k.pdf

Dependence between the Photochemical Age of Light Aromatic Hydrocarbons and the Carbon Isotope Ratios of Atmospheric Nitrophenols

Atmospheric aerosol measurements conducted at Environment Canada's observation sites at Alert, Nunavut and the peak of Whistler Mountain, British Columbia are compared with simulations from the global chemical transport model GEOS-Chem with the two-moment bin aerosol microphysics module TOMAS and with the Canadian Atmospheric Global Climate Model (CanAM4). The year-long comparisons show generally good agreement in terms of volume and mass concentrations. The carbonaceous aerosol is underestimated by GEOS-Chem-TOMAS (previously noted by others) and the size distributions, while similar, indicate larger particles and lower number concentrations. The lower numbers and larger particles predicted by GEOS-Chem-TOMAS may be connected with the underestimated carbonaceous aerosol.

A comparison of measurements and global model simulations of the atmospheric aerosol at two remote sites

Annual concentrations of ice nucleating particles at different Arctic stations

. Carbonaceous aerosol is a major contributor to the total aerosol load and being monitored by diverse measurement approaches. Here, ten years of continuous carbonaceous aerosol measurements collected at the Centre of Atmospheric Research Experiments (CARE) in Egbert, Ontario, Canada on quartz filters by three independent networks (Interagency Monitoring of PROtected Visual Environments (IMPROVE), Canadian Air and Precipitation Monitoring Network (CAPMoN), and Canadian Aerosol Baseline Measurement (CABM)) were compared. Specifically, the study evaluated how differences in sample collection and analysis affected the yield of total carbon (TC), organic carbon (OC), and elemental carbon (EC). When all measurements were normalized with respect to concentration measured in a common reference year, OC measurements agreed to within 29–48 % and EC measurement to within 20 % amongst the different networks. Fitted with a sigmoid function, elevated OC and EC concentrations were found when ambient temperature exceeded 10 °C. These increased ambient concentrations of OC during summer were attributed to the secondary organic aerosol (SOA) formation and forest fire emissions, while elevated EC concentrations were attributed to forest fire emissions and increased vehicle emissions. The observations from this study suggest that carbonaceous aerosol measurements, especially EC, can be synchronized across networks if sample collection and analytical method in each network remain internally consistent. This study allows the generation of regional to continental-scale-harmonized concentration data sets for benchmarking of atmospheric chemical transport models that determine emission sources and sinks, and assess the effectiveness of government mitigation policies in improving air quality and reducing reliance on fossil fuel consumption.

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Inter-comparison of the Elemental and Organic Carbon Mass Measurements from Three North American National Long-term Monitoring Networks

/pdf/stable-carbon-isotope-ratios-of-ambient-volatile-organic-1i5j1avsmf.pdf

Lin Huang

Papers

Dependence between the Photochemical Age of Light Aromatic Hydrocarbons and the Carbon Isotope Ratios of Atmospheric Nitrophenols

A comparison of measurements and global model simulations of the atmospheric aerosol at two remote sites

Annual concentrations of ice nucleating particles at different Arctic stations

Inter-comparison of the Elemental and Organic Carbon Mass Measurements from Three North American National Long-term Monitoring Networks

Stable carbon isotope ratios of ambient volatile organic compounds