Effects of Black Carbon on Climate: Advances in Measurement and Modeling

Abstract

Black carbon (BC) particles are non-spherical agglomerates consisting of hundreds or thousands of graphitic carbon spherules the diameters of which are about 15-50 nm. The spherules are graphitic in their molecular states and are, thus, strongly light-absorbing. BC particles are emitted by the incomplete combustion of carbon-based fossil fuels and biomass. BC mass in the atmosphere resides in agglomerates typically between 100 and 600 nm in diameter. They influence the global radiation budget by strongly absorbing solar radiation in the visible wavelengths and by changing the albedo of snow through deposition. Radiative forcing (RF) of BC is defined as the change in net radiative flux at the top of the atmosphere in W m −2 due to a change of BC between the pre-industrial time and present-day periods. The instantaneous direct radiative forcing of airborne BC particles (BC DRF), which does not include climate feedbacks, is determined by their absorption cross sections and spatial distributions. The distributions of BC are, in turn, controlled by its emission, dynamical transport, and loss during transport. The absorption cross section of BC is controlled by its optical properties (i.e., refractive index) and microphysical properties (size distribution, morphology, and mixing state). Because it is crucial to characterize these parameters, we first developed techniques to measure them accurately. Newlydeveloped BC measurement technologies constitute the firm basis of our studies. The techniques were applied to laboratory experiments and field observations of BC particles in air and rainwater. We also developed regional scale three-dimensional (3D) models to quantitatively interpret the observational results. One of the models calculates BC aging and optical/radiative processes explicitly without parameterizations. The reliable field measurements and model calculations of BC has enabled an improved understanding of the physical and chemical processes that control the microphysical properties of BC. We also quantitatively analyzed the emission rate, transport, and wet removal processes of BC in Asia by comparing the observed, and model-calculated, BC distributions. Through aircraft measurements in the Arctic, we characterized emissions of BC from biomass burning and the strong seasonal variations of the efficiency of transport of BC from different regions in the northern hemisphere to the Arctic. A number of findings, brought about by the observational and modeling efforts, demonstrate the strength of our innovative methodologies for improving the estimate of BC DRF, which has been highly uncertain thus far.

Evaluation of ground‐based black carbon measurements by filter‐based photometers at two Arctic sites

“…For COSMOS, b sca is very close to zero for most aerosols, owing to the use of the heated inlet to remove volatile non‐BC species [ Kondo et al , ]. In fact, the contribution of the f sca b sca term of equation to b abs (COSMOS) values has been estimated to be about 2% at midlatitudes [ Kondo , ]. Hence, we used the following equation for COSMOS: …”

“…The time resolution of the measurement was maintained at 1 min. The M BC (COSMOS)/M BC (SP2) ratio was observed to decrease by about 7% with an increase in the mass median diameter (MMD) of 50 nm (from 130 to 180 nm) in Tokyo, possibly owing to the size dependence between MAC (COSMOS) and f fil [Kondo et al, 2011b;Kondo, 2015]. In Tokyo, the mean MMD was 146 ± 12 nm, with a mean geometrical standard deviation (σ gm ) of 1.82 ± 0.14.…”

“…Black carbon (BC) particles are emitted as a result of incomplete combustion of both natural and anthropogenic carbon-based fuels. BC particles influence the radiation budget of the Earth's atmosphere by strongly absorbing solar radiation [Bond et al, 2013;Kondo, 2015]. Warming is occurring in the Arctic at about twice the global average rate [Shindell and Faluvegi, 2009] owing to a combination of climate feedbacks, including radiation feedback [Sand et al, 2016].…”

Hygroscopicity of materials internally mixed with black carbon measured in Tokyo

“…Black carbon (BC) aerosols are emitted by incomplete combustion of carbonaceous matter such as fossil fuels and biomass. They absorb solar radiation and contribute to positive radiative forcing [Bond et al, 2013;Intergovernmental Panel on Climate Change, 2013;Kondo, 2015]. BC aerosols are become increasingly internally mixed with non-BC (inorganic, organic, or inorganic + organic) compounds during aging after their initial emission [Schneider et al, 2005;Shiraiwa et al, 2007;Matsui et al, 2013].…”

Airborne Aerosol in Situ Measurements during TCAP: A Closure Study of Total Scattering

“…Although Mie theory does allow for the RI-based corrections associated with both the real and imaginary parts of the complex RI [32][33][34], airborne measurements of aerosol chemical composition and absorbing components that are required for the RI estimation are demanding and not always available. The mass loading of black carbon (BC) is an example of one of these absorbing components with relatively sparse relevant measurements [4,35]. As a result, iterative schemes that use assumed values of complex RI in combination with other assumptions are commonly applied to minimize differences between the measured and calculated aerosol properties of interest, such as PM10 [34].…”