Aerosol particles microphysics

Eichel, C., M. Kramer, L. Schiitz, and S. Wurzler, The Water-Soluble Fraction of Atmospheric Aerosol Particles and Its Influence on Cloud Microphysics, J. Geophys. Res., 101, 29499-29510 (1996). 

The indirect climatic impact of aerosol at the ABL is determined by numerous interactions between aerosol and the dynamics of the microphysical and optical properties of clouds. The input to the atmosphere of anthropogenic aerosol particles functioning as CCN favors an increase in cloud droplet number density. As mentioned above, the related increase in the optical thickness and albedo of clouds, with their constant water content, was called the first indirect effect , which characterizes the climatic impact of aerosol. 

The impact of secondary aerosols on indirect radiative forcing is the most variable and is the least understood [3]. The reasons why the indirect effect of secondary aerosols is so difficult to describe is that it depends upon [1] (1) a series of molecular-microphysical processes that connect aerosol nucleation to cloud condensation nuclei to cloud drops and then ultimately to cloud albedo and (2) complex cloud-scale dynamics on scales of 100-1000 km involve a consistent matching of multiple spatial and time scales and are extremely difficult to parameterize and incorporate in climate models. Nucleation changes aerosol particle concentrations that cause changes in cloud droplet concentrations, which in turn, alter cloud albedo. Thus, macro-scale cloud properties that influence indirect forcing result from both micro-scale and large-scale dynamics. To date, the micro-scale chemical physics has not received the appropriate attention. 

Mlcrophyslcs - aerosol and cloud A variety of microphysical models accounting for condensational growth, evaporation and coagulation of aerosol particles in the sub- and supersaturated regimes, and cloud droplets in supersaturation, are available to investigate the evolution of condensed material under conditions of varying temperature and humidity. 

Based on the use of the NARCM regional model of climate and formation of the field of concentration and size distribution of aerosol, Munoz-Alpizar et al. (2003) calculated the transport, diffusion, and deposition of sulfate aerosol using an approximate model of the processes of sulfur oxidation that does not take the chemical processes in urban air into account. However, the 3-D evolution of microphysical and optical characteristics of aerosol was discussed in detail. The results of numerical modeling were compared with observational data near the surface and in the free troposphere carried out on March 2, 4, and 14, 1997. Analysis of the time series of observations at the airport in Mexico City revealed low values of visibility in the morning due to the small thickness of the ABL, and the subsequent improvement of visibility as ABL thickness increased. Estimates of visibility revealed its strong dependence on wind direction and aerosol size distribution. Calculations have shown that increased detail in size distribution presentation promotes a more reliable simulation of the coagulation processes and a more realistic size distribution characterized by the presence of the accumulation mode of aerosol with the size of particles 0.3 pm. In this case, the results of visibility calculations become more reliable, too. 

The current version of GEM-AQ has five size-resolved aerosols types, viz. sea salt, sulphate, black carbon, organic carbon, and dust. The microphysical processes which describe formation and transformation of aerosols are calculated by a sectional aerosol module (Gong et al. 2003). The particle mass is distributed into 12 logarithmically spaced bins from 0.005 to 10.24 pm radius. This size distribution leads to an additional 60 advected tracers. The following aerosol processes are accounted for in the aerosol module nucleation, condensation, coagulation, sedimentation and dry deposition, in-cloud oxidation of SO2, in-cloud scavenging, and below-cloud scavenging by rain and snow. 

The modal approach assumes a shape for the particle-size distribution, typically one or more lognormal distributions, and represents evolution of the size distribution as evolution of the parameters characterizing the distribution, i.e., the amplitude, mode radius, and variance for the lognormal distribution (Binkowski and Shankar, 1995 Wilck and Stratmann, 1997). This approach offers the possibility of representing aerosol microphysical properties in models with far fewer variables (modal parameters) than are required in the sectional method (numbers of particles in each bin). 

Marlow WH. Survey of aerosol interactive forces. In Aerosol Microphysics I Particle Interaction Marlow WH, ed. McGraw-Hill New York, 1980 116-156. 

In air, permanent solid particles (atmospheric aerosols) occur either from primary sources out of the atmosphere or from gas-to-particle conversion within the atmosphere. All trace matter shows a high variability in concentration because of chemical and microphysical processes. Liquid particles (cloud, fog and rain droplets), however, are not permanent in air and form and exist only under specific physicochemical conditions (the presence of condensation nuclei and water vapor saturation). The transition from molecules to droplets comprises many steps ... 

It is out of the scope of this book to describe the AP mechanics, i. e. microphysics and dynamics (Friedlander 1977, Hinds 1882, Kouimtzis and Samara 1995, Harrison and van Grieken 1998, Meszaros 1999, Spumy 1999, 2000, Baron and Willeke 2001). Here, we only summarize the important topic of atmospheric aerosol size distribution (Jaenicke 1999). Fig. 4.15 shows that the size range covers several orders of magnitude. Therefore, the common logarithm of the radius is useful to describe the different distribution functions dN r)ld gr = f( gr) or dN r)ldr =/(Igr)/2.302 r. N r) cumulative number size distribution (or the integral of radii) having dimension cm , r radius of particle ... 

Inhaled particulate matter is susceptible to capture by the body in the respiratory system. Depending upon the particle s size, this may occur anywhere from the nose or mouth for the largest particles down to the lung s alveoli for the smallest (under 200 nm). Since the respiratory system presents an environment to the aerosol that is quite different from that outside the body, particle growth and transformation frequently occur, complicating the analysis of deposition mechanisms [1.31,32]. Aerosol microphysical domains of relevance include the thermodynamics of particle growth, kinetic theory, interaction forces,and some aspects of homogeneous nu-cleation theory. 

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