Aerosol System Parameters

The essential features of this discussion are available in HIDY and BROCK [2.6]. Consequently, only a brief review will be given. 

Aerosol particles in nature and many technical applications are very complex in terms of their morphology, internal structure, chemical composition, etc. As a consequence, little progress has been made in dealing with this complexity in terms of theories of evolution of aerosols. A very large set of parameters is necessary to describe an aerosol system. 

Many current theories for aerosol systems begin with the assumption that the particles are rigid spheres. This permits some reduction in the complexity. Additional simplification is also made by assuming that the gas is monatomic or that for specific systems a polyatomic gas may be treated as a monatomic gas. 

In this idealized model, some of the important dimensionless parameters frequently appearing in the study of aerosols are  

The subscript i represents a property of the particles of radius R. . is the mean velocity of particles relative to the host gas. v. is the mean thermal speed of particles. HIDY and BROCK [2.6] give a detailed discussion of these and other parameters of importance for ultrafine particles. 

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The question of particle shape is a complex problem and we are still at the sti e where we are developing methods to see if we can characterize adequately the range of shapes within a powder and their effect on the powder system and/or the aerosol system. It is becoming apparent that some complex problems will require more than one method of characterization thus if one was inhaling a complex soot particle the aerodynamic diameter which governs the penetration of the lung is one parameter whereas the fractal structure is another needed to assess the potential health hazard of the inhaled aerosol particle. 

The inference of cloud characteristics is based on much less sophisticated approaches than those for determining thermal stmcture and gas abundances. Clouds tend to be quite inhomogeneous compared with gaseous mixtures and require more parameters for adequate definition. Also, the appropriate equation of transfer [Eq. (2.1.40)] is considerably more complex than Eq. (8.2.1), and not nearly as amenable to inversion techniques. Even so, direct techniques are sometimes capable of leading to rather definitive conclusions about cloud and aerosol systems. We illustrate with an example concerning the abundance of the photochemical aerosol in Titan s stratosphere. 

Even though all three reactors share the same precursor delivery system, each tool offers specific advantages. For example, a cold-wall reactor (reactor B) helps prevent decomposition of the precursor before it reaches the substrate. A pulsed aerosol injection system at low pressure (reactor C) allows the film to grow under better-defined conditions than in a continuous process (reactor A) because of the minimization of undesirable transient effects caused by the high volatility of the solvents used.46 A more detailed description of each of the conditions for film growth, including reactor type, precursor type, delivery method, deposition temperature, growth time, and other parameters are summarized in Table 6.2. Depositions were done on bare and Mo-coated... 

Table 4.3.1 Parameters for the Formation of AgBr Particle in Aerosol OT-n-Heptane System...

Without an appreciation for the possible spread of sizes in real particulate systems the values of a in Fig. 11.6 are merely those of an adjustable parameter. We therefore give distribution widths for some natural and artificial aerosols and hydrosols in Table 11.1 we excluded from this list broad distributions, such as raindrops, to which the notion of a width is not really applicable. 

Later, Lizio et al. [78] used a new aerosol delivery system (ASTA-ADS) to investigate the pulmonary absorption and tolerability of four different cetrorelix formulations delivered as nebulized aerosols to orotracheally cannulated rats. After only 5 min exposure to the cetrorelix aerosol, serum testosterone concentrations were reduced to subnormal levels over a 24-h period. After dose adjustment (dose delivered minus exhaled amount), the bioavailabilities for pulmonary delivery ranged from 48.4 27.0% to 77.4 44.0% compared to IV administration. In addition, the lung function parameters did not reveal any formulation-related changes. Overall, the results of cetrorelix aerosol administration compared well with those obtained with intratracheal instillation of cetrorelix solution [77]. 

Many experimental parameters and components affect sensitivity, including the analyte transport efficiency of the sample introduction system and the mean size and size distribution of the aerosol entering the ICP. The plasma torch design, rf generator, load coil, interface between the atmospheric pressure ICP and mass spectrometer, ion optics, mass spectrometer itself, and detector also affect sensitivity. 

It is necessary to highlight the effects of aerosols and other chemical species on meteorological parameters, which have many different pathways (direct, semi-direct, and indirect effects, etc.) and they have to be prioritised and considered in on-line coupled modelling systems. Sensitivity studies are needed to understand the relative importance of different feedback mechanisms for different species and conditions relevant to air quality and climate interactions. A concerted action to mobilise and coordinate research in this area is needed. 

During a February 1981 oceanographic cruise in the western South Atlantic Ocean, we used our system aboard the USNS Hayes to sample marine aerosols automatically for 16 days at 1.5-h intervals along the cruise track shown in Figure 1. The sea-salt aerosol concentrations were determined for correlation with wind speed and other relevant meteorological parameters. This chapter identifies the most important variables and the extent to which they affect modeling of salt loads in the marine atmosphere. 

A basic understanding of the nebulizer function and the types of nebulizers is necessary to successfully interface CE to the ICP-MS. Nebulization, as previously described, is the process to form an aerosol, i.e., to suspend a liquid sample into a gas in the form of a cloud of droplets. The quality of any nebulizer is based on many different parameters including mean droplet diameter, droplet size distribution, span of droplet size distribution, droplet number density, and droplet mean velocity. There are numerous nebulizers commercially available for the use with ICP-MS systems, and their detailed description can be found elsewhere.Pneumatic designs, both concentric and cross flow, are the most popular for CE interfaces with the occasional use of the ultrasonic nebulizer (USN). Figure 2 shows some typical nebulizers. The pneumatic nebulizer is either a concentric design (Fig. 2A), where both the gas stream and the liquid flow in... 

Beclometasone dipropionate is the most widely dispensed inhaled anti-inflammatory agent for astfunatic human patients. Inhaled beclometasone dipropionate reduces inflammatory cell populations in bronchoalveolar lavage fluid, controls clinical signs of airway obstruction and improves parameters of pulmonary function in human asthmatics. Consequently, aerosolized beclometasone dipropionate is the first line of therapy for mod-erate-to-severe allergic airway disease in human patients. Aerosolized beclometasone does not cause adrenal suppression in asthmatic human patients at therapeutic dosages (800-1600 xg/day) and initiation of beclometasone therapy as a replacement for systemic corticosteroid administration permits recovery of the hypothalamic-pituitary-adrenal axis (Barnes et al 1998). 

In asthmatic human patients, fluticasone propionate improves asthma symptoms and parameters, improves pulmonary function and reduces pulmonary inflammation and airway reactivity (Barnes et al 1998). Regular fluticasone reduces or eliminates the need for rescue 2 agonist therapy and produces progressive improvement in airway reactivity and pulmonary function. In clinical studies, equivalent efficacy is demonstrated with one-quarter of the dose of fluticasone compared with flunisolide and budesonide, and equivalent efficacy is demonstrated with one-half of the dose of fluticasone compared with beclometasone. Adrenal function is less affected by fluticasone propionate at therapeutic doses than with beclometasone, flunisolide or budesonide. Although all aerosolized corticosteroids are considered safe, fluticasone has the least potential for adverse systemic effects and has the most favorable therapeutic index. 

Ruchatz F, Kleinebudde P, Muller BW. Residual solvents in biodegradable microparticles. Influence of process parameters on the residual solvent in microparticles produced by the aerosol solvent extraction system (ASES) process. J Pharm Sci 1997 86 101-105. 

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