Improved technique for measuring the size distribution of black carbon particles in liquid water

<p>We developed an improved technique for measuring the size distribution of black carbon (BC) particles suspended in liquid water to facilitate quantitative studies of the wet deposition of BC. The measurement system, which consists of a nebulizer and a single-particle soot photometer, incorporates two improvements into the system that we developed earlier. First, we extended the upper limit of the detectable BC size from 0.9 μm to about 4.0 μm by modifying the photo-detector for measuring the laser-induced incandescence signal. Second, we introduced a pneumatic nebulizer (Marin-5) with a high extraction efficiency (∼50.0%) that was independent of particle diameter up to 2.0 μm. For BC mass concentrations less than 70 μg L⁻¹, we experimentally showed that the diameters of BC particles did not appreciably change during the Marin-5 extraction process, consistent with theoretical calculations. Finally, we demonstrated by laboratory experiments that the size distributions of ambient BC particles changed little during their growth into cloud droplets under supersaturation of water vapor. Using our improved system, we measured the size distributions of BC particles simultaneously in air and rainwater in Tokyo during summer 2014. We observed that the size distributions of BC particles in rainwater shifted to larger sizes compared with those observed in ambient air, indicating that larger BC particles in air were removed more efficiently by precipitation.</p> <p>Copyright © 2016 American Association for Aerosol Research</p

Development of an openable small cyclone for atmospheric particulate matter sampling for toxicological experiments

The chemical components and mechanisms underlying the toxicity and adverse health effects of particulate matter (PM) in the atmosphere have not been fully elucidated. After designing a small, openable, stainless steel cyclone to collect PM samples effectively in powder form for use in toxicological experiments, we evaluated its performance. We compared it with a commercially available aluminum cyclone of similar dimensions, but which is unopenable. The aerodynamic cutoff diameter of the openable cyclone was found by experimentation to be approximately 0.2 µm at a flow rate of 90 L min−1, which is comparable to the unopenable commercial cyclone. The sampling yields, representing the fraction of obtained sample mass relative to the total mass of PM with aerodynamic diameter smaller than 2.5 μm (PM2.5) drawn into the sampler, were approximately 1.3 times higher, on average, for the openable cyclone than for the unopenable cyclone. The openable design of the cyclone might contribute to a marked increase in the finally obtained amounts of PM samples. Analyses of metal concentrations in the PM samples collected simultaneously using the stainless steel openable cyclone and aluminum unopenable cyclone suggest that the stainless steel cyclone is less likely than the aluminum cyclone to cause sample contamination from its material. The openable cyclone developed for this study facilitates the effective collection of powder-form PM samples suitable for use in toxicological experiments.</p

The Origin of Capacity Fade in the Li₂MnO₃·Li<i>M</i>O₂ (<i>M</i> = Li, Ni, Co, Mn) Microsphere Positive Electrode: An <i>Operando</i> Neutron Diffraction and Transmission X‑ray Microscopy Study

The mechanism of capacity fade of the Li₂MnO₃·Li<i>M</i>O₂ (<i>M</i> = Li, Ni, Co, Mn) composite positive electrode within a full cell was investigated using a combination of <i>operando</i> neutron powder diffraction and transmission X-ray microscopy methods, enabling the phase, crystallographic, and morphological evolution of the material during electrochemical cycling to be understood. The electrode was shown to initially consist of 73(1) wt % <i>R</i>3̅<i>m</i> Li<i>M</i>O₂ with the remaining 27(1) wt % <i>C</i>2/<i>m</i> Li₂MnO₃ likely existing as an intergrowth. Cracking in the Li₂MnO₃·Li<i>M</i>O₂ electrode particle under <i>operando</i> microscopy observation was revealed to be initiated by the solid-solution reaction of the Li<i>M</i>O₂ phase on charge to 4.55 V vs Li⁺/Li and intensified during further charge to 4.7 V vs Li⁺/Li during the concurrent two-phase reaction of the Li<i>M</i>O₂ phase, involving the largest lattice change of any phase, and oxygen evolution from the Li₂MnO₃ phase. Notably, significant healing of the generated cracks in the Li₂MnO₃·Li<i>M</i>O₂ electrode particle occurred during subsequent lithiation on discharge, with this rehealing being principally associated with the solid-solution reaction of the Li<i>M</i>O₂ phase. This work reveals that while it is the reduction of lattice size of electrode phases during charge that results in cracking of the Li₂MnO₃·Li<i>M</i>O₂ electrode particle, with the extent of cracking correlated to the magnitude of the size change, crack healing is possible in the reverse solid-solution reaction occurring during discharge. Importantly, it is the phase separation during the two-phase reaction of the Li<i>M</i>O₂ phase that prevents the complete healing of the electrode particle, leading to pulverization over extended cycling. This work points to the minimization of behavior leading to phase separation, such as two-phase and oxygen evolution, as a key strategy in preventing capacity fade of the electrode