Aerosol particles solubility

Condensed phase interactions can be divided roughly into two further categories chemical and physical. The latter involves all purely physical processes such as condensation of species of low volatility onto the surfaces of aerosol particles, adsorption, and absorption into liquid cloud and rainwater. Here, the interactions may be quite complex. For example, cloud droplets require a CCN, which in many instances is a particle of sulfate produced from SO2 and gas-particle conversion. If this particle is strongly acidic (as is often the case) HNO3 will not deposit on the aerosol particle rather, it will be dissolved in liquid water in clouds and rain. Thus, even though HNO3 is not very soluble in... 

Clearance to pulmonary lymph nodes will occur at a fractional rate of 0.0001 per day. Dissolution of the deposited particles and absorption of cerium into the systemic circulation will occur at rates that are between the extremes represented by CeCh in CsCl particles and Ce oxide or Ce in fused aluminosilicate particles as given by the functions included in Figure 9. These rates should not be expected to be constant over the entire clearance period and will depend upon the overall composition of the bulk aerosol particles, which indude particle size, amount of stable lanthanide present, acidity, and the solubility of other components of the particles. The accuracy of predicting respiratory tract clearance and internal organ uptake of radiocerium will depend heavily upon adequate determination of the particle solubility characteristics. 

Like the inhaled gases or vapors, soluble and insoluble aerosol particles can directly exert desirable and undesirable local effects at the site of deposition and/or systemic effects after solubilization, absorption, and metabolization. 

HC1 is efficiently absorbed into H2S04-H20 and into HN03-H2S04-H20 solutions, which as discussed earlier, are found in the stratosphere in the form of aerosol particles and Type I PSCs under some conditions (Wolff and Mulvaney, 1991). The solubility of HC1 in these liquid solutions can be expressed in terms of the usual Henry s law constant (Elrod et al., 1995 Abbatt, 1995 Luo et al., 1995 Hanson, 1998). Table 12.4 shows some typical measurements of the Henry s law constants for HC1 in several typical binary and ternary solutions, respectively. Hanson (1998) has shown that the solubility data for HC1 in binary mixtures of H2S04 and water in these and other studies can be fit by the form... 

Measurements of the solubility of HBr in sulfuric acid at 220 K gave Henry s law constants from 8.5 X 103 M atm-1 for 72 wt% H2S04 to 1.5 X 107 M atm-1 for 54 wt% H2S04 (Williams et al., 1995 Abbatt, 1995). Application of these values to stratospheric aerosol particles typical of midlatitude conditions gives very small equilibrium concentrations of dissolved HBr i.e., most of the HBr will remain in the gas phase. 

As we have seen in Chapter 9, there are a variety of dissolved solutes in atmospheric particles, which will lower the vapor pressure of droplets compared to that of pure water. As a result, there is great interest in the nature and fraction of water-soluble material in atmospheric particles and their size distribution (e.g., Eichel el al., 1996 Novakov and Corrigan, 1996 Hoffmann et al., 1997). This vapor pressure lowering effect, then, works in the opposite direction to the Kelvin effect, which increases the vapor pressure over the droplet. The two effects are combined in what are known as the Kohler curves, which describe whether an aerosol particle in the atmosphere will grow into a cloud droplet or not under various conditions. 

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 most important chemical parameter affecting the deposition and subsequent mobility of radioactive aerosols, such as the nuclides 90Sr and 137Cs examined in this study, is their solubility in rainwater. If these aerosols are dissolved in precipitation, the main factor in their transport is the movement of the rainwater, not the transport of insoluble aerosol particles. Huff and Kruger (2) examined the solubility products of strontium and chemically similar compounds which may carry trace amounts of 90Sr, and they estimated that strontium should be soluble in precipitation. Solubility tables also indicate that cesium compounds likely to exist in precipitation should be soluble. It was noted that the possibility did exist that some of the fission product "Sr and 137Cs might be bound within the structure of insoluble natural aerosols or nuclear weapon debris. 

The problem of estimating aerosol transport is thus focused on the study of watershed media effects on the transport of substances in solution rather than in insoluble aerosol particles. Thus, sorption by watershed media is a prime factor in determining the hydrologic transport of soluble radioaerosols, such as cesium and strontium. Removal of soluble radioaerosol elements from runoff by formation of insoluble compounds is considered unlikely. 

A second factor in the deposition process is the physical size of the radioaerosol particles deposited during dry deposition. Particle size affects the efficiency of foliar collection of dry aerosol particles and may also be important in determining the rate of solution of soluble constituents within the aerosol particle. Lockhart et al. (7) indicated that nuclear debris in surface level air is generally associated with aerosol particle sizes about 0.5-1.0p in diameter. Martell (8) stated that high yield detonations causing condensation of "Sr at stratospheric altitudes leads to the formation of particles with diameters less than 1 fi. Hence,... 

In addition, size reduction can also enhance delivery of poorly water-soluble APIs to the respiratory tract. SpeciLcally, aerosolized particles should have aerodynamic diameters in the range of 1-5(xm. With larger particles, deposition occurs primarily on the back of the throat, which can lead to systemic absorption and undesired side effects. 

Carbon-, nitrogen-, and sulfur-containing species account for most of the mass of aerosol particles. In spite of years of effort by many investigators, the exact chemical forms of carbon, sulfur, and nitrogen in these particles are not known nor are the formation mechanisms of these species known with certainty. There are many reasons for this situation, including the complexity of the system and the dependence of the apparent chemical composition on the analytical methods used. For example, wet chemical analyses of sulfur and nitrogen species report only ions in solution. These ions, however, may be originally water soluble (e.g., sulfate and ammonium from ammonium sulfate), or they may be ionic products of hydrolyzable species such as amides (1). Of course, insoluble species will not be detected by wet chemical techniques. 

However, not every aerosol particle serves as CCN. Accumulation mode aerosols provide the nuclei for most cloud drops (Penner et al., 2001). As in the case of anthropogenic and natural sulphate particles, OAs can also serve as CCN (Ramanathan et al., 2001). Additionally, the presence of water-soluble organic compounds in the particles and the presence of soluble gases (HN03) in the atmosphere can amplify the CCN activity of the aerosols and further increase the concentration of cloud droplets and the indirect forcing (Charlson et al., 2001). Also, biomass... 

Sullivan, A.P., R.J. Weber, A.L. Clements, J.R. Turner, M.S. Bae, and J.J. Schauer. 2004. A method for on-line measurement of water-soluble organic carbon in ambient aerosol particles Results from an urban site. Geophys. Res. Lett. 31 L13105/1-L13105/4. 

While in the air compartment, the contaminant solubilizes in the vapor-liquid phase or is associated with aerosol particles by adsorption. It is also prone to desorption from the aerosol particles into the vapor phase. Relevant properties of the air used to model transport of partitioning of a contaminant in the air compartment include temperature, turbulence, wind speed, size and composition of aerosol particles, etc.16,19 Relevant properties of the contaminant that measure its tendency to partition among the vapor, liquid, and solid phases in the air include its aqueous solubility (Saq), vapor pressure (VP), Henry s constant... 

Many atmospheric aerosol particles are water soluble and hygroscopic (i.e., absorb water with... 

Chemical Properties of Aerosols. Surface chemical properties of aerosol particles can also be tailored to improve deaggregation [273]. Hygroscopic particles absorb water when inhaled into the humid airways [282-284], increasing particle size and density in the process, as well as creating the potential for capillary bridge formation between particles. Hygroscopic growth can be reduced by the use of hydrophobic additives [285] or compounds with low aqueous solubility [286,287]. 

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