Aerosol particles sulfate

The significance of this oxidation of S(IV) in sea salt particles is that if it occurs in existing aerosol particles, sulfate formation will not result in new particles and hence potentially new CCN, but rather contribute to the mass of existing particles (e.g., O Dowd et al., 1997b). A significant fraction of all particulate nss is believed to be generated by this oxidation in existing sea salt particles. 

There is a large variety of atmospheric sulfur compounds, in the gas, solid, and liquid phases. Table 7-3 lists a number of gaseous compounds, range of concentration, source, and sink (where known). As this list illustrates, a significant number of these gases contribute to the existence of oxidized sulfur in the forms of SO2 and sulfate aerosol particles. Table 7-4 lists the oxy-acids of sulfur and their ionized forms that could exist in the atmosphere. Of these the sulfates certainly are dominant, with H2SO4 and its products of neutralization with NH3 as the most frequently reported forms. 

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... 

We will illustrate the necessity of including solute from CCN by a simple calculation, recalling that pH = 5.6 is the supposed equilibrium value for water in contact with 300 ppm of CO2. (That calculation will appear later.) In clean, marine air, the concentration of submicrometer aerosol particles (by far the most numerous) is small, say 0.25 pg m . It is known from measurements that the molecular form is often NH4HSO4, and we assume it is all dissolved in 0.125 g/m of liquid water in a cloud - which is typical for fair-weather marine clouds. Thus the average concentration of sulfate ion [SO4 ], mol/L, is... 

Sulfate compounds (e.g., NH4HSO4) form a major constituent of aerosol particles in remote, unpolluted marine air. 

The value of steel corrosion rate ratio for Viriato and Quivican stations at six months of exposure (1154.67/108.37 = 10.65) is between Cl-DR and chloride concentration in corrosion products ratio and is higher than sulfate. There should be rapid changes in chloride concentrations due to liquid precipitations and arrival of aerosol particles. Changes in sulfate concentration should be lower than for chloride. The corrosion rate in coastal zones should depend mainly on a sum of time of wetness at different chloride and sulfate concentrations. 

The Owens Lake brine analysis of Table V Indicates that the Na/S ratio should be approximately 3.8 for lake bed materials, which agrees quite well with the ambient ratio measured at Keeler. The above data suggests that airborne sulfur aerosols measured in the Owens Valley are in the form of sulfates which are suspended from the efflorescent crust on the Owens Lake bed. Therefore, if we assume that all the sulfur measured at each site is in the form of sulfate, then during a dust storm, the sulfate standard for the state of California (25pg/m ) is violated near the Owens Lake. It should be noted that the sulfate standard was developed for very fine acidic aerosols. The sulfates measured here are larger and basic particles, so their toxicity may be different from particles for which the standard was written. The calculated sulfate levels at each site during a dust storm are listed in Table VI. 

It should be noted that there are likely to be some aerosol particle components that are not readily detectable by the techniques in use now. For example, Kao and Friedlander (1995) have suggested that compounds such as H202 and free radicals that may be important toxicologically would have reacted prior to particle analysis and that species formed from such reactions, e.g., sulfate, may be used as markers of their presence. 

Vossier, T. L., and E. S. Macias, Contribution of Fine Particle Sulfates to Light Scattering in St. Louis Summer Aerosol, Environ. Sci. Technol., 20, 1235-1243 (1986). 

Sulfate aerosol particles with diameters typically in the 0.1- to 0.3-jum range are well known to be formed... 

There are a number of measurements documenting changes in NO and NO. in the stratosphere after the Mount Pinatubo eruption and which have been attributed to the removal of oxides of nitrogen due to reactions on aerosol particles. For example, a decrease in stratospheric NOz after the eruption followed by a return to normal levels has been reported (e.g., see Van Roozendael et al., 1997 and De Maziere et al., 1998). Similarly, NO decreases of up to 70% were reported, as well as increases in gaseous HN03 (much of that produced on the sulfate particles is released to the gas phase) (e.g., see Coffey and Mankin, 1993 Koike et al., 1993, 1994 David et al., 1994 Webster et al., 1994 and Rinsland et al., 1994). 

FIGURE 14-29 Calculated direct radiative forcing due to sulfate aerosol particles (adapted from Penner et al., 1998). 

The first major link between the indirect effects of aerosol particles and climate is whether there has been an increase in particles and in CCN due to anthropogenic activities. As discussed in Chapter 2, anthropogenic emissions of particles and of gas-phase precursors to particles such as S02 have clearly increased since preindustrial times, and it is reasonable that CCN have also increased. Ice core data provide a record of some of the species that can act as CCN. Not surprisingly, sulfate and nitrate in the ice cores have increased substantially over the past century (Mayewski et al., 1986, 1990 Laj et al., 1992 Fischer et al., 1998). For example, Figure 14.43 shows the increases in sulfate and nitrate since preindustrial times in an ice core in central Greenland (Laj et al., 1992). Sulfate has increased by 300% and nitrate by 200%. This suggests that sulfate and nitrate CCN also increased, although not necessarily in direct proportion to the concentrations in the ice core measurements. 

In addition to the differences in geographical distribution of the greenhouse gases compared to the aerosol particles and the day-night differences, there are also differences in their temporal behavior. As discussed earlier, typical residence times for sulfate particles are about a week, whereas that of C02 is about 100 years. As a result, the impacts of sulfate aerosols are almost immediately manifested, whereas those due to C02 occur over decades to centuries (Schwartz, 1993). 

Calhoun, J. A., T. S. Bates, and R. J. Charlson, Sulfur Isotope Measurements of Submicrometer Sulfate Aerosol Particles over the Pacific Ocean, Geophys. Res. Lett, 18, 1877-1880 (1991). Capaldo, K. P., and S. N. Pandis, Dimethylsulfide Chemistry in the Remote Marine Atmosphere Evaluation and Sensitivity Analysis of Available Mechanisms, J. Geophys. Res., 102, 23251-23267 (1997). 

Van Dingenen, R., F. Raes, and N. R. Jensen, Evidence for Anthropogenic Impact on Number Concentration and Sulfate Content of Cloud-Processed Aerosol Particles over the North Atlantic, J. Geophys. Res., 100, 21057-21067 (1995). 

Leaderer, B. P., P. M. Boone, and S. K. Hammond, Total Particle, Sulfate, and Acidic Aerosol Emissions from Kerosene Space Heaters, Environ. Sci. Technol., 24, 908-912(1990). 

As Martell has pointed out (30), in the region of the stratospheric large particle layer near 18-20 km. altitude, radioactive aerosol particles become attached to natural sulfate particles in the size range of about 0.1-0.4 jumeter radius. Subsequent upward transport of the radioactive aerosols is opposed by gravitational sedimentation. This combination of processes affords an explanation for the observed accumulation of 210Pb near 20 km. in the tropical stratosphere (2). At higher latitudes where slow mean motions are directed poleward and downward, no such accumulation is possible. 

Atmospheric aerosols are complex mixtures of particles derived from diverse sources. Soot from diesel engines, fly ash from coal combustion, and sulfates, nitrates, and organic compounds produced by atmospheric reactions of gaseous pollutants all contribute to the aerosol. Particle size and composition depend upon the conditions of aerosol formation and growth and determine the effects of atmospheric aerosols on human health, ecosystems, materials degradation, and visibility. Much of the research on environmental aerosols has focused on fine particles ranging from a few micrometers in... 

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. 

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