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S. Cho M.Sc. Ph.D. D. V. Michelangeli M.Sc. Ph.D. 《International Journal of Environmental Science and Technology》2008,5(1):1-10
In this study, variations in the size distributions due to different assumptions for the coagulation kernel are investigated. In order to evaluate how the coagulation kernel influences the form of the particle size distribution and to describe the process of the Brownian coagulation, the Brownian coagulation kernel, including the van der Waals forces, is compared with the most frequently used coagulation coefficients. Retardation should be considered for interparticle interactions for particles larger than 1μm radius. However, for particle sizes larger than 0.1 μm, the Brownian kernel is not dominant, so the retardation effect can be ignored. The inclusion of the van der Waals forces in the Brownian coagulation kernel caused a faster coagulation process in the small particle size range. Taking account of the turbulent coagulation kernel, the turbulent coagulation kernel becomes more important when the turbulent intensity is higher. The turbulent coagulation kernel affects the large particle size range and ignoring the turbulent coagulation kernel will lead to overestimation of particle number concentration in model simulation. The results of this study indicate that the inclusion of van der Waals forces or the turbulent coagulation kernel in the total coagulation kernel impacts on the modeled particle size distributions and total particle number concentration. 相似文献
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Operator splitting techniques are widely used in atmospheric modeling in order to reduce the cost of time integration and allow more flexibility by treating each operator separately. However, this is not error free and the magnitude of the error depends on whether the splitted operators commute or not and the magnitude of the splitting time step. In multiphase models, the gas and the aqueous phase chemistries are related through the gas-droplet mass transfer processes. In the present paper, we show that splitting the gas chemistry operator from the aqueous chemistry and mass transfer operator is not appropriate and leads to errors beyond the tolerated thresholds. Analytical expressions for the splitting errors are derived and numerical experiments are conducted. The LAMP chemical mechanism is employed. Time integration is performed with LSODE. 相似文献
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A one-dimensional cloud model with size-resolved microphysics and size-resolved aqueous-phase chemistry, driven by prescribed
dynamics, has been used to study gas scavenging by weak precipitation developed from low-level, warm stratiform clouds. The
dependence of the gas removal rate on the physical and chemical properties of precipitation has been explored under controlled
initial conditions. It is found that the removal of four gaseous species (SO2, NH3, H2O2 and HNO3) strongly depends on the total droplet surface area, regardless the mean size of droplets. The removal rates also correlate
positively with the precipitation rate, especially for precipitation having a mean radius larger than 20 μm. The dependence
of the scavenging coefficients on the total droplet surface area is stronger than on the precipitation rate.
The removal rates of SO2, NH3 and H2O2 by precipitation strongly depend on the others' initial concentrations. When NH3 (or H2O2) concentration is much lower than that of SO2, the removal rate of SO2 is then controlled by the concentration of H2O2 (or NH3). The removal of NH3 (or H2O2) also directly depends on the concentration of SO2. NH3 and H2O2 can also indirectly affect each other's removal rate through interaction with SO2. The scavenging coefficient of SO2 increases with the concentration ratio of NH3 to SO2 if the ratio is larger than 0.5, while the scavenging coefficient of NH3 increases with the concentration ratio of SO2 to NH3 when the ratio is smaller than 1. The scavenging coefficient of H2O2 generally increases with the concentration ratio of SO2 to H2O2. Although the Henry's law equilibrium approach seems to be able to simulate gas scavenging by cloud droplets, it causes large
errors when used for simulating the scavenging of soluble gas species by droplets of precipitating sizes. 相似文献
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Peter A. Taylor P-Y. Li Diane V. Michelangeli Jagruti Pathak Wensong Weng 《Boundary-Layer Meteorology》2007,125(2):305-328
A time and height dependent eddy diffusion model is used to investigate possible scenarios for the size distribution of dust
in the lower atmosphere of Mars. The dust is assumed to either have been advected from a distant source or to have originated
locally. In the former case, the atmosphere is assumed to initially contain dust particles with sizes following a modified
gamma distribution. Larger particles are deposited relatively rapidly while small particles are well mixed up to the maximum
height of the afternoon boundary layer and are deposited more slowly. In other cases, a parameterization of the dust source
at the surface is proposed. Model results show that smaller particles are rapidly mixed within the Martian boundary layer,
while larger particles (r > 10 μm) are concentrated near the ground with a stronger diurnal cycle. In all simulations we assume
that the initial concentration or surface source depend on a modified gamma function distribution. For small particles (cross-
sectional area weighted mean radius, reff = 1.6 μm) distributions retain essentially the same form, though with variations in the mean and variance of the area-weighted
radius, and the gamma function can be used to represent the particle size distribution reasonably well at most heights within
the boundary layer. In the case of a surface source of larger particles (mean radius 50 μm) the modified gamma function does
not fit the resulting particle size distribution. All results are normalised by a scaling factor that can be adjusted to correspond
to an optical depth for assumed particle optical scattering properties. 相似文献
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Solar Mesosphere Explorer (SME) observations of the 3 a.m. 1.27 micrometers nightglow at 45 N latitude, averaged over the period 10-31 July 1984, are reported. From the deduced volume emission rates, we derive the O2(a1 delta g) night-time production rates for the 80-100 km altitude range. Utilizing the mean SME-acquired 3 p.m. ozone profile for the same latitude and time period and an updated photochemical model, we determine night-time O, O3, H, OH, HO2, and H2O2 profiles. These are used in calculating the rates of reactions which are sufficiently exothermic to produce O2(1 delta) or excited states of OH or HO2, which could transfer their energy to O2 to form O2(1 delta). Of these reactions, most have rates that are quite small compared with the observed night-time O2(1 delta) production rate. For several others, laboratory experiments have found O2(1 delta) yields which are insufficient for simulating the observed O2(1 delta). Using yields of O2(1 delta) based on published laboratory and observational studies, we find that the sum of two reaction sequences can approximate the SME measurements: (1) O+O+M and (2) H+O3 followed by OH*+O2. 相似文献
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