Models aerosol dynamics

We have investigated the atmospheric implications ot our newly calculated absorption cross sections with the Garcia-Solomon 2D dynamical/chemical model [85,86], to which we have added sultur chemistry and aerosol microphysics [87]. The model spans 56 pressure levels trom 2 to 112 km above sea level, and 36 latitudes trom 89.5°S to 89.5°N. Further details ot the sultur chemistry and... 

In this concern one of the important tasks is to develop a modelling instrument of coupled Atmospheric chemistry/Aerosol and Atmospheric Dynamics/Climate models for integrated studies, which is able to consider the feedback mechanisms, e.g. aerosol forcing (direct and indirect) on the meteorological processes and climate change (see Fig. 1.2). 

MADRID secondary organic aerosol model (SORGAM) The model of aerosol dynamics, reaction, ionization, and dissolution... 

CAC-Aerosol Dynamics Modal model Log-normal modes nuclei, accumulation, coarse Moment equations coagulation, condensation... 

We emphasize at the outset that our objective is a comparison of concepts—homogeneous equilibrium versus aerosol dynamics. It is done in the context of two models but is not intended to apply only to those models. By keeping everything in the two models the same, apart from the aerosol model, we shall focus sharply on the difference in predictions arising solely from the nature of the aerosol model. 

Both aerosol modeling and more fundamental atomistic and molecular level models have been applied to this problem. Aerosol dynamics modeling has lead to a better understanding of the individual steps that comprise the formation of particles, all the way from nucleation to subsequent growth. Both molecualar orbital and reaction rate theory was used as sources of fundamental data for input to the aerosol dynamics model. A simplistic molecular dynamics computation has been used to explain the particle morphology observed. 

Aerosol Dynamics. Inclusion of a description of aerosol dynamics within air quaUty models is of primary importance because of the health effects associated with fine particles in the atmosphere, visibiUty deterioration, and the acid deposition problem. Aerosol dynamics differ markedly from gaseous pollutant dynamics in that particles come in a continuous distribution of sizes and can coagulate, evaporate, grow in size by condensation, be formed by nucleation, or be deposited by sedimentation. Furthermore, the species mass concentration alone does not fliUy characterize the aerosol. The particle size distribution, which changes as a function of time, and size-dependent composition determine the fate of particulate air pollutants and their... 

Simulation of aerosol processes within an air quaUty model begins with the fundamental equation of aerosol dynamics which describes aerosol transport (term 2), growth (term 3), coagulation (terms 4 and 5), and sedimentation (term 6) ... 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

Over recent years, increased computational power and improved efficiency have allowed significant developments and improvements to be applied to climate models [19], including the improved representation of dynamical processes such as advection [20] and an increase in the horizontal and vertical resolution of models. It has also enabled additional processes to be incorporated in models, particularly the coupling of the atmospheric and ocean components of models, the modelling of aerosols and of land surface and sea ice processes. The parame-terisations of physical processes have also been improved. 

A different approach which also starts from the characteristics of the emissions is able to deal with some of these difficulties. Aerosol properties can be described by means of distribution functions with respect to particle size and chemical composition. The distribution functions change with time and space as a result of various atmospheric processes, and the dynamics of the aerosol can be described mathematically by certain equations which take into account particle growth, coagulation and sedimentation (1, Chap. 10). These equations can be solved if the wind field, particle deposition velocity and rates of gas-to-particle conversion are known, to predict the properties of the aerosol downwind from emission sources. This approach is known as dispersion modeling. 

Nazaroff, W. W., and G. R. Cass, Mathematical Modeling of Indoor Aerosol Dynamics, Environ. Sci. Technol., 23, 157-166 (1989a). 

Meng, Z., D. Dabdub, and J. H. Seinfeld, Size-Resolved and Chemically Resolved Model of Atmospheric Aerosol Dynamics, J. Geophys. Res., 103, 3419-3435 (1998). 

Kumar P, Ketzel M, Vardoulakis S, Pirjola L, Britter R (2011) Dynamics and dispersion modelling of nanoparticles from road traffic in the urban atmospheric environment -a review. J Aerosol Sci 42 580-603... 

W.D. Griffiths, F. Boysan, Computational fluid dynamics (CFD) and empirical modelling of the performance of a number of cyclone samplers, J. Aerosol Sci. 27 (1996) 281-304. 

A simple calculation of the lifetime of MSA in cloud water can be made using model estimates of the free radical chemistry of cloud droplets. The OH concentration in cloud water is a complex function of both the gas and aqueous phase chemistry and the dynamics of gas/liquid exchange. A recent model (21) estimated cloudwater OH concentration as 2-6 x 10 M for droplets of 5 -30/im radius. Using the rate constant measured here (4.7 x 107 M 1 s 1), this yields a lifetime of 1.2 3.5 hours. Considering that the lifetime of a nonraining cloud is on the order of a few minutes to an hour, some fraction of the MSA present could react with OH, presumably being converted to sulfate. While such a process may lower the concentratron of MSA in the droplet, it would only have a minor effect on the cloudwater sulfate levels because of the typically low MSA non-sea-saIt sulfate ratio in the aerosol entering the cloud. 

---