Atmospheric particles organic aerosols

Table 7-2 includes most of the main gaseous constituents of the troposphere with observed concentrations. In addition to gaseous species, the condensed phases of the atmosphere (i.e. aerosol particles and clouds) contain numerous other species. The physical characteristics and transformations of the aerosol state will be discussed later in Section 7.10. The list of major gaseous species can be organized in several different ways. In the table, it is in order of decreasing concentration. We can see that there are five approximate categories based simply on concentration ... 

The NO + 03 chemiluminescent reaction [Reactions (1-3)] is utilized in two commercially available GC detectors, the TEA detector, manufactured by Thermal Electric Corporation (Saddle Brook, NJ), and two nitrogen-selective detectors, manufactured by Thermal Electric Corporation and Antek Instruments, respectively. The TEA detector provides a highly sensitive and selective means of analyzing samples for A-nitrosamines, many of which are known carcinogens. These compounds can be found in such diverse matrices as foods, cosmetics, tobacco products, and environmental samples of soil and water. The TEA detector can also be used to quantify nitroaromatics. This class of compounds includes many explosives and various reactive intermediates used in the chemical industry [121]. Several nitroaromatics are known carcinogens, and are found as environmental contaminants. They have been repeatedly identified in organic aerosol particles, formed from the reaction of polycyclic aromatic hydrocarbons with atmospheric nitric acid at the particle surface [122-124], The TEA detector is extremely selective, which aids analyses in complex matrices, but also severely limits the number of potential applications for the detector [125-127],... 

R ardless of the chemistry, there are some physical constraints on aerosol-gas interactions. Particles must be close to or at equilibrium with respect to the surrounding vapor to exist in air for any substantial period. Thus, the partial pressure of condensed species on particles must be less than or equal to the saturation vapor pressure at atmospheric temperature for stability. As shown later in this chapter, the requirement of low vapor pressure is particularly important to the stability of organic aerosols. 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

Infrared and Raman spectroscopy. Stephens and Price (1970, 1972) used infrared spectroscopy to examine both ambient and laboratory-generated aerosols. They identified sulfate, nitrate, and ammonium ion absorption bands in ambient particles as well as bands indicating the presence of organics in diesel exhaust (C-H) and oxidized organics in irradiated hydrocarbon-NO, . mixtures. Since then, many studies using IR have been carried out and a variety of species identified, including COf , PO4-, and SiO A See Chapter 9.C.2 and Figs. 9.49, 9.50, and 9.51 for some typical FTIR spectra of atmospheric particles. 

This requisite surface area is more than three orders of magnitude higher than one would expect for organic aerosols (e.g., 2 m2 g-1 particle for organic-rich aerosols from urban atmospheres (Liang et al., 1997)). This result strongly suggests that absorption is the key process. 

Calvert and McQuigg suggest that yet unknown radicals, such as 0CH20 or those derived from it, formed in the 03-olefin-air mixtures may oxidize S02 in the homogeneous reaction. It is known that OH and H02 radicals combine rapidly with S02. The addition products may eventually be transformed into sulfuric acid, peroxysulfuric acid, sulfates, and nitrates in a polluted atmosphere probably in a liquid phase of aerosol particles, although the detailed steps are still unknown. Finlayson and Pitts (357) believe that the oxidation of aromatic compounds by such species as OH, H02, 03, and 0(3P) may also be significant for the formation of organic aerosol. 

O Dowd CD, Aalto P, Hameri K, Kulmala M, Hoffmann T (2002) Aerosol formation atmospheric particles from organic vapours. Nature 416 497 -98... 

Atmospheric particles in the troposphere are composed of a complex mixture of highly water-soluble inorganic salts, insoluble mineral dust, and carbonaceous material (which includes organic compounds plus elemental carbon) (Jacobson et al., 2000). Studies in which the chemical composition has been determined as a function of particle size demonstrate a correlation between the chemical composition and the size mode of atmospheric aerosols (Meszaros et al., 1997 Krivacsy and Molnar, 1998 Alves et al.,2000 Maenhaut et al.,2002 Smolik et al., 2003 Samara andVoutsa, 2005). 

Nowadays, thermo-optical methods are considered the most reliable measurement techniques for OC/EC split in atmospheric aerosols. Nevertheless, methods for TC/EC/BC analysis in atmospheric particles are still open to debate and their different analytical approaches have been the main cause for performing intercomparison studies (Schmid et al., 2001 ten Brink et al., 2004). The TC measurements showed good agreement, whereas the results of EC/BC determinations were highly variable due to EC overestimation by thermal methods. Furthermore, caution must be taken when using BC as an estimative of the EC content in aerosols, and vice versa BC and EC measurements are associated to the carbon content of colored and refractory organic compounds, respectively, which can lead to substantially different results between methods (Poschl, 2005). 

The organic fraction present in atmospheric particles is a highly complex mixture, which makes the speciation of individual compounds a difficult task. The traditional analytical approach has usually been solvent extraction of aerosol particles collected in a filter followed by gas chromatographic separation coupled to mass spectrometry (GC-MS) detection for individual compound identification and quantification. Although a large number of compounds, sometimes in trace amounts, have been... 

The studies of Facchini et al. (2000), Gysel et al. (2004), Kiss et al. (2005) and Dinar et al. (2006) highlight the importance of organic aerosol components in the cloud-nucleating activities of atmospheric particles. However, a question still remains to be answered What is the truly effect of organic components on aerosol CCN activity Furthermore, does the WSOM enhance cloud droplet activation or, on the other hand, delay droplet activation ... 

Limbeck, A., Kulmala, M., and Puxbaum, H. (2003). Secondary organic aerosol formation in the atmosphere via heterogeneous reaction of gaseous isoprene on acidic particles. Geophys. Res. Letters 30,1996, doi 10.1029/2003GL017738. 

Samburova, V., Zenobi, R., and Kalberer, M. (2005). Characterization of high molecular weight compounds in urban atmospheric particles. Atmos. Chem. Phys. 5, 2163-2170. Sannigrahi, P., Sullivan, A. P, Weber, R. I, and Ingall, E. D. (2006). Characterization of water-soluble organic carbon in urban atmospheric aerosols using solid-state 13C NMR spectroscopy. Environ. Sci. Technol. 40, 666-672. 

Tabazadeh, A. (2005). Organic aggregate formation in aerosols and its impact on the physicochemical properties of atmospheric particles. Atmos. Environ. 39,5472-5480. 

Similarly, the relative humidity has a strong influence on the chemical composition of the secondary organic aerosol formed in the atmosphere by the reaction of ozone with 1-tetradecene <2000EST2116> thermal desorption particle beam mass spectrometric determinations found that the main products are a-hydroxytridecyl hydroperoxide and a peroxy-hemiaceta 1. 

Several areas in which chemical measurement technologies have become available and/or refined for airborne applications have been reviewed in this paper. It is a selective review and many important meteorological and cloud physics measurement capabilities of relevance to atmospheric chemistry and acid deposition (e.g., measurement of cloud liquid water content) have been ignored. In particular, we have not discussed particle size spectra measurements for various atmospheric condensed phases (aerosols, cloud droplets and precipitation). Further improvements in chemical measurement technologies can be anticipated especially in the areas of free radicals, oxidants, organics, and S02 and N02 at very low levels. Nevertheless, major incremental improvements in the understanding of acid deposition processes can be anticipated from the continuing airborne application of the techniques described in this review. 

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