查看更多>>摘要：? 2022Characterizing soot oxidation kinetics is crucial for understanding how gasoline particulate filters (GPFs) perform both in terms of filtration efficiency and pressure drop. The most common method for measuring soot oxidative reactivity is thermogravimetric analysis (TGA). Because TGA is an offline method, it may inaccurately predict how soot oxidizes on a GPF, especially if a catalytic washcoat is present that may enhance oxidation rates through surface interactions as the soot loads on the filter. In this work, a novel in-situ soot oxidative reactivity measurement method was developed. The method involved loading a catalytic GPF under high temperature conditions conducive to soot oxidation and measuring the filtration efficiency of 100 nm particles. A correlation was made between filtration efficiency and loaded soot mass on the filter to allow calculation of the soot oxidation rate. The method was evaluated in experiments using a 2.0 L gasoline direct injection (GDI) engine with three oils of varying additive packages, including an oil with a high zinc dialkyldithiophosphate (ZDDP) concentration, a non-additive, pure poly-alpha olefin (PAO) oil, and an oil with a high concentration of calcium sulfonate. Calculated specific soot oxidation rates ranged from ～0.06–0.6 min?1 and showed strong dependence on GPF inlet gas temperature and lubrication oil additive type. The results clearly demonstrated a catalytic effect of calcium-containing ash particles. Reactivity of soot produced by the engine running with the high calcium containing lubrication oil was increased. Similarly, the results indicated that the catalytic washcoat on the filter increased soot oxidation rates on-filter, especially at low soot loading. Conversely, the ZDDP oil additive exhibited a reactivity inhibiting effect, resulting in lower soot oxidation rates. This work represents the first known in-situ soot oxidative reactivity measurements on a GPF and elucidates the effect of lubrication oil additives and catalytic washcoat on oxidation rate.
查看更多>>摘要：? 2022Filter-based devices were found to underestimate PM2.5 mass concentrations due to the evaporation loss of semi-volatile inorganic materials (SVIM). To reduce the evaporation-induced PM2.5 loss, the chilled Teflon filter sampler (CTF) was developed in which the sampling air was chilled to low temperatures (T) of 4–7 °C after dehumidification. The CTF with the aerosol flow dehumidified to low relative humidity (RH) of 25.50 ± 4.88% by using a Nafion dehumidifier and chilled at 4 °C showed an accurate measurement for the total ion concentration with the mean normalized bias (MNB) of +4.17 ± 8.96% as compared to the actual value measured by the porous denuder sampler (PDS). In comparison, the normal single Teflon filter sampler (STF) sampled PM2.5 ion concentration at ambient T and RH showed a negative MNB of ?14.26 ± 13.66%. It indicates that the 4 °C CTF can suppress the evaporation loss of SVIM and measure actual ion concentrations accurately. However, 4 °C CTF over-measured PM2.5 concentrations with the MNB of +15.01 ± 7.99% as compared to ?10.40 ± 5.92% of the STF, due to normal and capillary condensations of water vapor although the condensed water on particles prevented SVIM evaporation loss. After correcting for the remaining water concentration determined by using surrogate TiO2 nanoparticles, the accuracy of PM2.5 concentrations was improved significantly with the MNB of only about +2.93 ± 8.56%. To avoid excessive remaining water, the CTF was chilled to 7 °C and found to be able to reduce the evaporation loss of SVIM while measuring PM2.5 concentrations accurately with the MNB of +4.92 ± 6.52% without remaining water correction in most sampling days.
查看更多>>摘要：? 2022 Elsevier LtdAutomobile cabin air filters (ACAFs) play an important role in protecting passengers from health risks associated with exposure to high concentrations of particulate matter (PM). Therefore, understanding the filtration mechanism of ACAFs is essential to assessing human exposure to PM. Despite the importance of ACAFs, changes in filter performance over their operation time remain largely uncharacterized; therefore, prediction of the service life of air filters is unreliable. In this study, changes in the performance of ACAFs were analyzed according to operating time under laboratory and on-road driving dust loading conditions. In the laboratory, with constant temperature and humidity, the filtration efficiency increased from 87.5% to 99.1% with increased loading time in the particle size range of 0.3–0.5 μm. This increase occurs as air paths narrow due to the clogging caused by dust, which increases filtration efficiency and causes a pressure drop. However, under on-road driving conditions, filter performance dropped to 58.7% with similar dust loading. These results indicate that dust loading, which is the most widely used variable in service life estimation, is not sufficient to characterize the service life of an ACAF. Therefore, additional studies are needed to evaluate and establish certification parameters and test methods for determining the service life of an ACAF. The present study provides useful baseline information on the lifespan of ACAFs, which will help to improve automotive cabin indoor air quality.
查看更多>>摘要：? 2022 Elsevier LtdQuantum chemical calculations have proven to describe the thermodynamics of sub-nanometre clusters more accurately than the liquid drop model used in classical nucleation theory (CNT). However, the standard quantum chemical free energies of multicomponent clusters are fundamentally incompatible with the quantity appearing in the exponential of the CNT expression for the nucleation rate. The origin of this incompatibility is known to be in the statistical thermochemistry, but it is also connected to a much debated issue of self-consistency within CNT. Although these issues do not affect the main results of previous theoretical studies of nucleation, a thorough analysis and discussion about the nature of free energy in quantum chemistry of cluster formation has been missing. In this study, we present a consistent definition for the formation free energy using the law of mass action and a general equilibrium cluster distribution function, and apply this definition to gas-phase quantum thermochemical calculations. This internal consistency allows us to integrate the high-level thermochemical data to the basic framework of CNT and the liquid drop model contained therein. Moreover, based on our analysis, we derive a simple analytical expression for the steady-state nucleation rate compatible with the widely used numerical ACDC model. As an illustrative example, the consistent formation free energies and nucleation rates are presented and analysed for atmospherically relevant H2SO4–NH3 clusters at various temperature and monomer vapour pressure conditions.
查看更多>>摘要：? 2022 Elsevier LtdNumerical simulations are carried out to study the effects of aerosol particles acted as cloud condensation nuclei (CCN) and ice nuclei (IN) on thunderstorm properties. A two-cylinder time-dependent cloud and aerosol interaction model with the spectral bin microphysical parameterization, explicit noninductive electrification and lightning process is utilized to explore the impacts. This model not only uses the high-resolution particle size bins to describe the distributions of aerosol particles and hydrometeors, but also can be applied to study the diffusional growth of aerosol particles to cloud droplets and to track the mass of both CCN and IN in hydrometeors. The simulated cloud properties show that increased CCN concentrations result in more numerous but smaller droplets and form ice particles less efficiently, producing less numbers of graupel and less efficient conversion to raindrops. Increased IN concentrations directly enhance the heterogeneous nucleation, and then boost the subsequent microphysical processes, contributing to the production of increasingly numbers of graupel which eventually pass through the melting layer and then enhance the precipitation. As CCN concentrations increase, the charge density gained by different mass-binned ice particles and total charge density significantly decrease due to reduced large ice particles with greater diameters than 360 μm. In contrast, as IN concentrations are further increased, dramatically increased large ice particles with greater diameters than 360 μm are produced and thus, support the enhanced charge density gained by different mass-binned ice particles and total charge density. Besides, as expected, the reduced (enhanced) lightning frequency is well explained by the reduced (increased) numbers of large ice particles (diameter>360 μm).
查看更多>>摘要：? 2022 Elsevier LtdThe impact of a single yttria (Y2O3) nanoparticle onto a yttria substrate was studied as a function of particle velocity (300–1200 m/s) and diameter (5–12 nm) for three particle orientations and two substrate orientations using molecular dynamics simulations. Impacts resulted in minimal dislocation motion but extensive disordering of the crystal lattice without approaching the melting temperature. The resulting amorphous microstructure was both precisely coincident with plastic strain and retained until the end of the simulation, suggesting a deformation mechanism of amorphization-facilitated viscous flow. Further analysis revealed that the degree of amorphization depended primarily on the impact velocity and secondarily on the orientations of the particle and substrate, with significant second-order effects from variable interactions.
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