Aerosol dynamics

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) ... 

The secondary source of fine particles in the atmosphere is gas-to-particle conversion processes, considered to be the more important source of particles contributing to atmospheric haze. In gas-to-particle conversion, gaseous molecules become transformed to liquid or solid particles. This phase transformation can occur by three processes absortion, nucleation, and condensation. Absorption is the process by which a gas goes into solution in a liquid phase. Absorption of a specific gas is dependent on the solubility of the gas in a particular liquid, e.g., SO2 in liquid H2O droplets. Nucleation and condensation are terms associated with aerosol dynamics. 

Aerosol dynamics are based on spherical particles, a premise which almost never exists in practice. However, if there is consistency in handling the aerosol dynamics calculations, the aerodynamic diameter (see Section 13.5.2.2) that is measured gives fairly accurate predictions of aerodynamic behavior. As a result, the difference between the real shape and size of the particles and the aerodynamic shape and size is unimportant for most practical purposes. 

Gelbard, F., Tambour, Y. and Seinfeld, J.H., 1980. Sectional representations for simulating aerosol dynamics. Journal of Colloid and Interfacial Science, 76, 541. 

McGraw, R. (1997). Description of aerosol dynamics by the quadrature method of moments. Aerosol Science and Technology 27, 255-265. 

White, W. H., R. B. Husar, and S. K. Friedlander. A Study of Los Angeles Smog Aerosol Dynamics by Air Trajectory Analyses. Paper 73-111 Presented at the 66th Annual Meeting of the Air Pollution Control Association, Chicago, Illinois, June 24-28, 1973. 25 pp. 

Clarke, A. D., Z. Li, and M. Kitchy, Aerosol Dynamics in the Equatorial Pacific Marine Boundary Layer Microphysics, Diurnal Cycles, and Entrainment, Geophys. Res. Lett., 23, 733-736 (1996). 

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). 

S.K. Friedlander. Smoke, Dust, and Haze Fundamentals of Aerosol Dynamics. Oxford, New York, second edition, 2000. 

This theory, as originated from the early work of Smoluchowski [20], nowadays has numerous applications in several branches of chemistry, such as colloidal chemistry, aerosol dynamics, catalysis and the physical chemistry of solutions as well as in the physics and chemistry of the condensed state [21-24]. Until recently, its branch called standard chemical kinetics [12, 15, 16] based on the law of mass action seemed to be quite a complete and universal theory. However, because of their entirely phenomenological character, theories of this kind always operate with the reaction rates K which are postulated to be time-independent parameters. 

An important current problem is attaining sufficient understanding of atmospheric aerosol dynamics to develop mathematical models capable of relating emission reductions of primary gaseous and particulate pollutants to changes in ambient aerosol loadings and thereby to improvements in visibility and health effects. These models involve thermodynamics, transport phenomena, and chemical kinetics in an intricate equilibrium and... 

MADE/SORGAM module The Modal Aerosol Dynamics Model for Europe (MADE) with the... 

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

Single aerosol type. J Geophys Res 103 6123-6132 Ackermann U, Hass H, Memmesheimer M, Ebel A, Binkowski FS, Shankar U (1998) Modal aerosol dynamics model for Europe development and first applications. Atmos Environ... 

Zhang Y, Seigneur C, Seinfeld JH, Jacobson MZ, Binkowski FS (1999) Simulation of aerosol dynamics a comparative review of algorithms used in air quality models. Aerosol Sci Technol 31 487-514... 

Zhang YB, Pun KV, Wu S-Y, Seigneur C, Pandis S, Jacobson M, Nenes A, Seinfeld J (2004) Development and application of the model for aerosol dynamics, reaction, ionization and dissolution (MADRID). J Geophys Res 109 D01202. doi 10.1029/2003JD003501... 

Tzivion S, Feingold G, I-evin Z (1989) The evolution of raindrop spectra. Part 11 Collisional collection/breakup and evaporation in arainshaft. J Atmos Sci 46 3312-3327 Wesely ML (1989) Parametrization of surface resistance to gaseous dry deposition in regional numerical models. Atmos Environ 16 1293-1304 Whitby ER, McMurry PH, Shankar U, Binkowski FS (1991) Modal aerosol dynamics modelling. Rep. 600/3-91A120, Atmospheric Research and Exposure Assessment Laboratory, U.S. 

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

The Enviro-HIRLAM (see its description and validation in a separate paper by Korsholm et al. in this volume) is a fully online NWP-ACT integrated system. The following steps towards Enviro-HIRLAM are being incorporated or have already been achieved (1) nesting of models for high resolutions, (2) improved resolution of boundary and surface layer characteristics and structures, (3) urbanisation of the model, (4) improvement of advection schemes, (5) implementation of chemical mechanisms, (6) implementation of aerosol dynamics, (7) realisation of feedback mechanisms, (8) assimilation of monitoring data (ongoing). 

For simulation of the aerosol (especially anthropogenic) effects more detailed microphysics in HIRLAM is needed, in the former version it is very difficult to consider all the aerosol indirect effects. The current STRACO (Soft TRAnsition condensation) scheme in HIRLAM (Sass 2002) needs modifications and gives a possibility of developing simpler indirect mechanisms. One of such feedback semi-empirical model was developed in Enviro-HIRLAM by Korsholm et al. (2008b). The new AROMA/HARMONIE cloud scheme (Pinty and Jabouille 1998 Caniaux et al. 1994) is more suitable for implementation of aerosol dynamics and indirect effects of aerosols (CCN) models, but will be more expensive computationally. So, the main focus of our collaboration in this field should be in the improvement of the cloud/microphysics and radiation schemes in HIRLAM. 

At the moment the cloud microphysics-aerosol interaction is included in HIRLAM in a very simple way in the convection schemes, where the cloud condensation nuclei have a lower concentration than over land. Enviro-HIRLAM includes the aerosol dynamics and their indirect effects on meteorology. The use of aerosol may also be prepared by making a 3D field of aerosol that has the characteristics of the currently prescribed values, then the extension to a real 3D distribution of aerosols that can interact with the microphysics is relatively straightforward. Sensitivity studies are needed to understand the relative importance of feedbacks. First experience of Enviro-HIRLAM indicates some sensitivity to effective droplet size modification in radiation and clouds. 

Modeling efforts aimed at simulating the worldwide diffusion of the cloud begin to appear preliminary results gave rather faster transit times than have actually been observed (Capone et al., 1983 Pitari et al., 1984). While these results may be due to the scarce resolution of the circulation models, they may also point to the rather complex nature of the aerosol dynamics (see e.g. Crescentini and Fiocco, 1983). Related anomalies were found by us in utilising the meridional distribution model of Cadle et al. (1976), in efforts to simulate the effects of Mt. Agung (Fiocco et al., 1977). 

Meng Z., Dabdub D., and Seinfeld J. H. (1998) Size-resolved and chemically resolved model of atmospheric aerosol dynamics. J. Geophys. Res. 103, 3419- 3435. 

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