Aerosol particle loss

Arctic at polar sunrise. The mechanism likely involves regeneration of photochemically active bromine via heterogeneous reactions on aerosol particles, the snow-pack, and/or frozen seawater. The source of the bromine is likely sea salt, but the nature of the reactions initiating this ozone loss remains to be identified. For a review, see the volume edited by Niki and Becker (1993) and an issue of Tellus (Barrie and Platt, 1997). 

Evidence for the contribution of the CIO + BrO interaction is found in the detection and measurement of OCIO that is formed as a major product of this reaction, reaction (31a). This species has a very characteristic banded absorption structure in the UV and visible regions, which makes it an ideal candidate for measurement using differential optical absorption spectrometry (see Chapter 11). With this technique, enhanced levels of OCIO have been measured in both the Antarctic and the Arctic (e.g., Solomon et al., 1987, 1988 Wahner and Schiller, 1992 Sanders et al., 1993). From such measurements, it was estimated that about 20-30% of the total ozone loss observed at McMurdo during September 1987 and 1991 was due to the CIO + BrO cycle, with the remainder primarily due to the formation and photolysis of the CIO dimer (Sanders et al., 1993). The formation of OCIO from the CIO + BrO reaction has also been observed outside the polar vortex and attributed to enhanced contributions from bromine chemistry due to the heterogeneous activation of BrONOz on aerosol particles (e.g., Erie et al., 1998). 

Figure 12.32 shows the results of model calculations of the effects of the increased aerosols for October 1986 at 43.5°N (Solomon et al., 1996). The calculated change in the odd-oxygen loss rate when the measured aerosol particle surface area is incorporated into the... 

Particle-Particle Interactions. Loss of strong acid content of aerosol particles can also occur because of reactions between co-collected acidic and basic particles impacted together on the collection surface. This phenomenon most frequently occurs as the result of interaction of coarse (>2.5 xm diameter), alkaline, soil-derived particles with fine (<2.5 xm diameter) acidic sulfate particles (66). Particle-particle interactions with net neutralization can be reduced in many cases by sampling with a virtual impactor or a cyclone to remove coarse particles, although this procedure does not prevent the effect if external mixtures of fine particles of different acid contents are sampled. In situ methods with shorter sampling times can be used such that these topochemical reactions are less likely to occur. 

Combining the physical aerosol measurements from a high number of European background stations shows that there are clear similarities between particle number size distributions and concentration levels measured at different locations over wide geographical regions. These similarities are connected to similar emissions, particle loss processes, and meteorological patterns. The main aim of this section is just to provide key factors of each station categorization, more details and complete analysis of individual stations are available in [18] and references therein. 

Kumar P, Fennell P, Symonds J, Britter R (2008) Treatment of losses of ultrafine aerosol particles in long sampling tubes during ambient measurements. Atmos Environ... 

The study described here demonstrates that ESCA provides information regarding the chemical nature of the surface of an unperturbed sample which would be difficult to acquire by other methods. A major weakness of ESCA, the necessity of exposing the sample to vacuum, together with its attendant problem of sample volatilization, can also be one of its strengths. The volatility of some nitrogenous species in atmospheric aerosol particles can be used to provide strong evidence for chemical identity of ionic compounds (e.g., ammonium nitrate) rather than simply ionic identities as provided by wet chemical methods. This volatility is accelerated by x-ray irradiation, so that similar results could be achieved only by extended vacuum exposure alone if another analytical technique were used. Also, with ESCA, volatile losses can be conveniently monitored since the sample remains in the spectrometer throughout the process. 

In general, the creation of aerosols is technically difficult, expensive, and time-consuming. Moreover, patients need to learn specific inhalation techniques for the correct use of inhaler devices [26], and many have difficulty in using MDIs properly. Aerosol preparations are associated with significant losses of drug. Furthermore, due to the inertial impaction of the administered aerosol particles,... 

During nebulization from airjet nebulizers, cooling of the reservoir solution occurs which, together with vapor loss, results in concentration of the dmg solution. This in turn produces an aerosol output in which the drag concentration increases with time. Concentration of the dmg solution in the reservoir can lead to drug recrystallization with subsequent blockage within the device or variation in aerosol particle size. 

The unique part of the Universal Interface is the membrane separator or gas diffusion cell which allows the solvent vapor to be efficiently removed with essentially no loss of sample contained in the aerosol particles. In this device the aerosol is transported through a central channel bounded on the sides by a gas diffusion membrane or filter medium which is in contact with a countercurrent flow of a sweep gas. For El mass spectrometry helium appears to be most useful for both the carrier and sweep gas. The properties of the... 

The particle loss rate for the chamber can be described as a first-order wall loss process (Cocker et al., 2001). Particle loss rates determined for the first set of aerosol experiments within the reactor is about 7 day. While maximum particle volume in experiments performed have ranged from less than 0.1 to almost 80 pg/m, no correlation between maximum particle volumes and measured decay rates has been seen (Carter et al., 2005). 

The decay of the number concentration with time at all sizes is evident over the first 12 hours or so in the DMPS measured size distribution. After this there is an obvious onset of nucleation and significant growth followed by decay in the aerosol number. The eycles of particle loss and fresh nucleation is repeated over several days, with no introduetion of precursor gases. The initial concentration of NaCl particles is eomparable to a low atmospheric loading and the nucleation is at a fairly low level. This illustrates the baekground level of aerosol dynamics which is currently experienced. This will improve with inereased scrubbing and cleaning procedures. 

The oxidation of S02 can also take place on the surface of existing aerosol particles. According to the laboratory work of Urone et ai (1968) the rate of the S02 oxidation can be rapid in the presence of aerosol particles, even without illumination. In caseofFe203 particles the S02 loss in the laboratory chamber air is as much as 100 % hr-1, while high loss rates were found in the presence of aluminum, calcium, chromium and other metal oxides as well. It is questionable, however, whether the S02 loss is due to chemical conversion or to simple physical adsorption (Corn and Cheng, 1972). Furthermore, in U rone s experiments the mass concentration of aerosol particles was 100-200 times greater than that of S02 which is unrealistic under atmospheric conditions. Finally, the experimental results of... 

An important consequence of the Brownian motion of aerosol particles is their collision and subsequent coalescence. This so-called coagulation process can be characterized by the particle loss per unit time (Hidy and Brock, 1970) ... 

It is concluded on the basis of equation [4.S] that the intensity of the particle loss due to the thermal coagulation is directly proportional to square of the particle concentration, while the coagulation efficiency increases with decreasing particle radius. This means that the coagulation of small particles at a high concentration is a very rapid process. Equation [4.S] is valid only for monodisperse aerosols, i.e. aerosols composed of particles of uniform size. However, the same qualitative conclusion can also be drawn in the case of polydisperse systems. 

Because of their small radius, the size and size distribution (see Subsection 4.3.2) of Aitken particles may be determined with a diffusion battery. This device is composed by an ensemble of capillary tubes, through which the air is drawn at low velocity. As a result of their Brownian diffusion, the smaller aerosol particles are deposited on the walls of the tubes during the aspiration. This particle loss is a function of the diffusion coefficient and consequently of the size of the particles (see equation [4.4]). 

The change of the mass concentration of aerosol particles (M) caused by washout can also be calculated easily. Let us designate by v(R) the falling speed of the drops with number concentration N(R). Suppose that this speed is much higher than the deposition velocity of the particles. Under these conditions the particle mass loss in the air per unit time is... 

It was mentioned in Chapter 4 that aerosol particles scatter and absorb solar radiation. These processes depend upon the concentration, size distribution, form, refractive index and absorption coefficient of the particles, as well as upon the wavelength of the radiation. In the case of water-soluble particles the extinction is also controlled by relative humidity (see Section 4.5). The energy absorbed by particles leads to an increase of temperature, while backscattering produces an energy loss for the system. Sines this energy loss may be characterized by the albedo, it is proposed to examine first the relation between albedo and temperature in surface air. 

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