Constraining the complex refractive index of black carbon particles using the complex forward-scattering amplitude

Black carbon is the largest contributor to global aerosol’s shortwave absorption in the current atmosphere and is an important positive climate forcer. The complex refractive index, m = mr + imi, the primary determinant of the absorbed and scattered energies of incident radiation per unit volume of particulate material, has not been accurately known for atmospheric black carbon material. An accurate value at visible wavelengths has been difficult to obtain due to the black carbon’s wavelength-scale irregularity and variability of aggregate shape, distribution in particle size, and mixing with other aerosol compounds. Here, we present a method to constrain a plausible (mr, mi) domain for black carbon from the observed distribution of the complex forward-scattering amplitude S(0°). This approach suppresses the biases due to the above-mentioned complexities. The S(0°) distribution of black carbon is acquired by performing single particle S(0°) measurements in a water medium after collecting atmospheric aerosols into water. We demonstrate the method operating at λ = 0.633 μm for constraining the refractive index of black carbon aerosols in the north-western Pacific boundary layer. From the plausible (mr, mi) domain consistent with the observed S(0°) distributions and the reported range of mass absorption cross-section, we conservatively select 1.95 + 0.96i as a recommendable value of the refractive index for uncoated black carbon at visible wavelengths. The recommendable value is 0.17 larger in mi than the widely used value 1.95 + 0.79i in current aerosol-climate models, implying a ∼16% underestimate of shortwave absorption by black carbon aerosols in current climate simulations.</p

Detection of Uranium and Chemical State Analysis of Individual Radioactive Microparticles Emitted from the Fukushima Nuclear Accident Using Multiple Synchrotron Radiation X‑ray Analyses

Synchrotron radiation (SR) X-ray microbeam analyses revealed the detailed chemical nature of radioactive aerosol microparticles emitted during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, resulting in better understanding of what occurred in the plant during the early stages of the accident. Three spherical microparticles (∼2 μm, diameter) containing radioactive Cs were found in aerosol samples collected on March 14th and 15th, 2011, in Tsukuba, 172 km southwest of the FDNPP. SR-μ-X-ray fluorescence analysis detected the following 10 heavy elements in all three particles: Fe, Zn, Rb, Zr, Mo, Sn, Sb, Te, Cs, and Ba. In addition, U was found for the first time in two of the particles, further confirmed by U L−edge X-ray absorption near-edge structure (XANES) spectra, implying that U fuel and its fission products were contained in these particles along with radioactive Cs. These results strongly suggest that the FDNPP was damaged sufficiently to emit U fuel and fission products outside the containment vessel as aerosol particles. SR-μ-XANES spectra of Fe, Zn, Mo, and Sn K−edges for the individual particles revealed that they were present at high oxidation states, i.e., Fe³⁺, Zn²⁺, Mo⁶⁺, and Sn⁴⁺ in the glass matrix, confirmed by SR-μ-X-ray diffraction analysis. These radioactive materials in a glassy state may remain in the environment longer than those emitted as water-soluble radioactive Cs aerosol particles