Aerosol formation, sulfuric acid

A special sulfur cycle is expressed as part of the Gaia hypothesis [48.5]. According to this the compound dimethyl sulfide (DMS) is produced by marine plankton in the oceans. It vaporizes to the atmosphere and is oxidized to an aerosol of sulfuric acid. On the nuclei of this aerosol, water droplets are formed, supporting cloud formation. The sulfur is brought back to the ocean with rain and the plankton production of... 

Similarly, SO2 and SO3 (SOJ compounds are produced in combustion by the oxidation of sulfur compounds within the fuel source. SO , emitted into the atmosphere can be incorporated into aerosol particles and wet-deposited as corrosive sulfuric acid. Both NO , and SO , emissions contribute to acid rain content from wet deposition, due to their participation in the formation of nitric and sulfuric acid, respectively. 

Chu et al. (1987) present results of laboratory studies of the formation of an ultrafine aerosol by converting SO- to sulfuric acid using measurement methods described by Holub and Knutson (1987) and Kulju et al. (1987). It was found that the size of the resulting activity distributions is dependent on the S02 concentration. The role of humidity is still unclear and more studies are needed, but it appears that both future theoretical models and laboratory studies will be extremely fruitful in elucidating the behavior of Po-218 from shortly after its formation until its incorporation into the existing accumulation mode aerosol. 

Although no conclusive evidence has been reported so far, the possible importance of organic sulfur species as sulfate aerosol precursors is supported by several observations. Sulfuric acids, sulfonic acids, and other organic sulfur compounds are formed in sulfur dioxide-hydrocarbon reactions at high concentrations. Organosulfiir radical species, such as RSO2 and RO2SO2 have been postulated as intermediates for these reactions. Suzuki (see Penzhom et o/. ) observed polymer formation from... 

Roedel, W., Measurement of Sulfuric Acid Saturation Vapor Pressure Implications for Aerosol Formation by Heteromolecular Nucleation, J. Aerosol Sci., 10, 375-386 (1979). 

The residence times of SO2 and H2S04 in the troposphere are typically only a few days, but sulfuric acid aerosols reaching the stratosphere can be very persistent together with nitric acid, they provide the solid surfaces in polar stratospheric clouds on which reaction 8.9 and related processes occur heterogeneously. Indeed, studies suggest that NOx emissions of commercial supersonic aircraft in the lower stratosphere may pose less of a threat to the ozone layer than previously supposed however, the accompanying formation of sulfuric and nitric acid aerosols may exacerbate ozone loss by increasing the available catalytic surface area. 

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. 

In Figure 3, the simulated ultrafme aerosol concentrations (in the size ranges defined in the legend) are compared to observations. It is remarkable that, even though sulfuric acid concentrations remained quite low most of the day (never exceeding lxl07/cm3), the ultrafme particle count rose dramatically late in the morning (after -10 00). Model calculations that include the IMN mechanism reproduce this behavior, whereas classical BHN theory would have forecast no particle formation under the circumstances. The calculated ultrafme particle abundances also appear to respond to... 

CCN). Changes in the concentrations of CCN may alter the cloud droplet concentration, the droplet surface reflectivity, the radiative properties of clouds (cloud albedo) (2), and hence, the earth s climate (8-101. This mechanism has been proposed for the remote atmosphere, where the radiative properties of clouds are theoretically predicted to be extremely sensitive to the number of CCN present (ID). Additionally, these sulfate particles enhance the acidity of precipitation due to the formation of sulfuric acid after cloud water dissolution (11). The importance of sulfate aerosol particles to both radiative climate and rainwater acidity illustrates the need to document the sources of sulfur to the remote atmosphere. 

The processes by which clouds incorporate sulfuric and nitric acids are conveniently distinguished into two categories depending upon whether oxidation takes place in the gas phase or in the aqueous phase, as illustrated schematically in Figure 1. For an examination of gas-phase atmospheric oxidation of SO2 and NO2 see (1,2). Products of this oxidation, aerosol sulfuric acid and sulfat and nitrate salts, and gas-phase nitric acid, are expected to be rapidly and to great extent incorporated into cloud droplets upon cloud formation 0,4). 

In continental air sulfate tends to be associated with finer particles, and as ammonia is more likely to be present in the air this can neutralize the sulfuric acid with the formation of ammonium sulfate- or bisulfate-containing particles over land. Sulfuric acid can displace chloride from seasalt aerosols and represent a source of hydrogen chloride ... 

The formation of ammonium sulfate and ammonium nitrate aerosols is an acid-base reaction in the atmosphere. Ammonia neutralizes the acids. Sulfuric acid has a very low vapor pressure (< 10 atm) and thus exists in the atmosphere as liquid particles, which react with NH3 and H2O (reaction 22). 

Clarke AD, Davis D, Kapustin VN, Eisele F, Chen G, Paluch I, Lenschow D, Bandy AR, Thornton D, Moore K, Mauldin L, Tanner D, Litchy M, Carroll MA, Collins J, Albercook G (1998) Particle nucleation in the tropical boundaiy layer and its coupling to marine sulfur sources. Science 282 89-92 Clarke AD, Kapustin, Eisele FL, Weber RJ, McMuny PH (1999) Particle production near marine clouds Sulfuric acid and predictions from classical binary nucleation. Geophys Res Lett 26 2425-2428 Clegg SL, Brimblecombe P, Wexler AS (1998) Thermodynamic model of the system H -NH/-Na -S04 -NO3 -CI -H2O at 298.15 K. JPhys Chem. A 102 2155-2171 Clement CF, Piijola L, dal Maso M, Ma kela JM, Kulmala M (2001) Analysis of particle formation bursts observed in Finland. J Aerosol Sci 32 217-236... 

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