The Effect of Weak Shear－induced Motion on Brownian Coagulation of Aerosol Particles

The coagulation rate of a dilute polydisperse aerosol dispersion of particles is considered for small Peclet number, which provides a measure of the ratio of the relative sheareinduced motion to Brownian motion betWeen two rigid spherical aerosol particles.The asymptotic form of the relative velocity of tWo unequal particles immerse in a simple shear flow when they are far apart is obtained.Using a singular pertllrbation method,a tWo term expansion for the dimensionless coagulation rate(Nusselt number) as function of the Peclet number is developed.In the limit of the radius of one of the two spheres becoming small,the result agrees with the dimensionless mass transfer rat6 to an aerosol particle at small Peclet number.

Eulerian-Lagranigan simulation of aerosol evolution in turbulent mixing layer

The formation and evolution of aerosol in turbulent flows are ubiquitous in both industrial processes and nature. The intricate interaction of turbulent mixing and aerosol evolution in a canonical turbulent mixing layer was investigated by a direct numerical simulation （DNS） in a recent study （Zhou, K., Attili, A., Alshaarawi, A., and Bisetti, F. Simulation of aerosol nucleation and growth in a turbulent mixing layer. Physics of Fluids, 26, 065106 （2014））. In this work, Monte Carlo （MC） simulation of aerosol evolution is carried out along Lagrangian trajectories obtained in the previous simulation, in order to quantify the error of the moment method used in the previous simulation. Moreover, the particle size distribution （PSD）, not available in the previous works, is also investigated. Along a fluid parcel moving through the turbulent flow, temperature and vapor concentration exhibit complex fluctuations, triggering complicate aerosol processes and rendering complex PSD. However, the mean PSD is found to be bi-modal in most of the mixing layer except that a tri-modal distribution is found in the turbulent transition region. The simulated PSDs agree with the experiment observations available in the literature. A different explanation on the formation of such PSDs is provided.

Source dynamics of carbonaceous aerosol during the haze bloom-decay process in China based on radiocarbon and organic molecular tracer

With the support by the National Natural Science Foundation of China and the Chinese Academy of Sciences,the research team led by Prof.Li Jun(李军)at the State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,illustrated the source dynamics of carbonaceous aerosol during the haze bloom-decay process in Beijing and Guangzhou based on

Differentially weighted operator splitting Monte Carlo method for simulating complex aerosol dynamic processes

A differentially weighted operator splitting Monte Carlo （DWOSMC） method is developed to solve com- plex aerosol dynamic processes by coupling the differentially weighted Monte Carlo method and the operator splitting technique. This method is validated by analytical solutions and a sectional method in different aerosol dynamic processes. It is first validated in coagulation and condensation processes, and nucleation and coagulation processes, and then validated through simultaneous nucleation, coagulation, and condensation processes. The results show that the DWOSMC method is a computationally efficient and quantitatively accurate method for simulating complex aerosol dynamic processes.

Wavelet Galerkin Methods for Aerosol Dynamic Equations in Atmospheric Environment

Aerosol modelling is very important to study and simulate the behavior of aerosol dynamics in atmospheric environment.In this paper,we consider the general nonlinear aerosol dynamic equations which describe the evolution of the aerosol distribution.Continuous time and discrete time wavelet Galerkin methods are proposed for solving this problem.By using the Schauder’s fixed point theorem and the variational technique,the global existence and uniqueness of solution of continuous time wavelet numerical methods are established for the nonlinear aerosol dynamics with sufficiently smooth initial conditions.Optimal error estimates are obtained for both continuous and discrete time wavelet Galerkin schemes.Numerical examples are given to show the efficiency of the wavelet technique.

Experimental-computational study of fibrous particle transport and deposition in a bifurcating lung model

Experiments carried out using a lung model with a single horizontal bifurcation under different steady inhalation conditions explored the orientation of depositing carbon fibers, and particle deposition frac- tions. The orientations of deposited fibers were obtained from micrographs. Specifically, the effects of the sedimentation parameter （γ）, fiber length, and flow rate on orientations were analyzed. Our results indicate that gravitational effect on deposition cannot be neglected for 0.0228 〈 γ 〈 0.247. The absolute orientation angle of depositing fibers decreased linearly with increasing y for values 0.0228 〈 γ 〈 0.15. Correspondence between Stokes numbers and y suggests these characteristics can be used to estimate fiber deposition in the lower airways. Computer simulations with sphere-equivalent diameter models for the fibers explored deposition efficiency vs. Stokes number. Using the volume-equivalent diameter model, our experimental data for the horizontal bifurcation were replicated. Results for particle deposition using a lung model with a vertical bifurcation indicate that body position also affects deposition.