Sulfuric particle formation

La Mer s qualitative interpretation of sulfur particle formation mechanism can be understood from the diagram shown in Fig. IV-13. The concentration of the molecularly dispersed sulfur formed in the above reaction slowly increases until critical supersaturation is reached. At that point nucleation and the formation of solid phase embryos take place. 

In addition to these nuclear reactions, myriads of other gas-phase transformations produce low-vapor pressure species, with the oxidation of SO2 and other reduced sulfur species dominating aerosol formation and growth. Oxidation of SO2 in the gas phase produces H2SO4, a readily condensable species that either combines with other molecules (new particle formation) or condenses on existing aerosols. 

We have seen in Chapter 8 that reactions in the aqueous phase present in the atmosphere in the form of clouds and fogs play a central role in the formation of sulfuric acid. Thus, an additional mechanism of particle formation and growth involves the oxidation of SOz (and other species as well) in such airborne aqueous media, followed by evaporation of the water to leave a suspended particle. 

Karcher, B and D. W. Fahey, The Role of Sulfur Emission in Volatile Particle Formation in Jet Aircraft Exhaust Plumes, Geophys. Res. Lett, 24, 389-392 (1997). 

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... 

Investigating Atmospheric Sulfuric Acid-Water-Ammonia Particle Formation Using Quantum Chemistry... 

The scope of this paper is to provide an overview of methods used to study properties of electrically neutral molecular clusters initiating particle formation in the troposphere, with focus on quantum chemistry. The review of results is intended to be complete with regard to water-sulfuric acid-ammonia clusters. Concerning studies on clusters including other molecular species, we review representative examples and newest publications. Ionic clusters and clusters involving iodine, related to coastal nucleation, are mentioned in passing. 

It was established by Yeliseyeva and Bakaeva (1968) that in the polymerization of polar monomers (MA) the decrease of emulsifier adsorption depends on tbe structure of the latter and for some types of emulsifiers may reach limiting values. This was observed in tbe polymerization ofMA in the presence of a mixed type of emulsifier, partially sulfurated with sulfuric acid oxyethylated alkylphenol (emulsifier C-I0 ). Its adsorption on the particle surface increases with the initial concentration and reaches > 100% filling of the adsorption layer, conditionally corresponding to 0.3S nm per molecule. Stable, concentrated latexes with small particles are formed. Therefore, emulsifier adsorption and the mechanism ctf particle formation associated with it depends not only on monomer polarity but also on the chemical structure of the emulsifier. 

The net effect of these two links between sulfur and halogen chemistry is to decrease the gas phase concentration of SO2 via a reduced yield of SO2 from the oxidation of DMS and the stronger aqueous phase sink for S(IV) which results in enhanced uptake of SO2 by droplets and aerosols. A critical prerequisite for new particle formation in the marine troposphere is the reaction chain ... 

Sulfuric acid. New particle formation involving H2SO4 has been investigated most intensively because there is strong evidence that sulfuric acid can be an important particle precursor. Gaseous sulfuric acid is formed via the oxidation of sulfur dioxide (SO2) by hydroxyl radical in the following multistep reaction ... 

Most of the nanoparticles emitted from diesel vehicles appear to nucleate from sulfuric acid and water during the cooling and dilution of the exhaust with ambient air (Kittelson 1998 Shi and Harrison 1999 Collings and Graskow 2000 Tobias et al. 2001). However, based on results from Shi and Harrison (1999), the measured rate of particle formation in diesel exhaust is much greater than the rate calculated from binary... 

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... 

Figure 9. Schematic diagram showing sulfur photochemistry in an anoxic, primitive atmosphere. The numbers at the base of the diagram indicate the oxidation state of the sulfur. Sulfur is emitted to the atmosphere from volcanoes as either SO2 or H2S. It is removed by rainout of soluble sulfur gases fS02, H2S, HS, HSO, and H2SO4) and by formation of sulfate and elemental sulfur particles (Engel and Macko. 199S).

At pH values around 6 the formation of sulfur was most rapid. Several metal salts like AICI3, Fe(NH4)2(S04)2 and K4[Fe(CN)6] decreased the induction period considerably while KCl, K2SO4, and MgCl2 had no effect. The growth of the sulfur particles was found to be diffusion controlled but the molecular nature of the particles was not investigated [48]. 

X-ray diffraction of sulfur particles excreted by Thiobacillus sp. showed the presence of orthorhombic sulfur crystals. The solubility of crystalline orthorhombic sulfur in water is known to be only 5 /tg 1 [42]. In the solubility test shown in Fig. 7 it was seen that the biologically produced sulfur particles can be dispersed in water but not in hexadecane, whereas crystalline orthorhombic sulfur is soluble in hexadecane but not in water. The reason for the observed hydrophilicity of the biologically produced sulfur particles has to be attributed to the hydrophilic properties of the surface of the sulfur particles. Because of the relatively high stability of the biologically produced sulfur particles at high salt concentrations, it is concluded that the colloidal stability is not merely based on electrostatic repulsion. It is known that hydrophobic sulfur can be wetted by Thiobacillus thiooxidans bacteria due to formation of organic surface-active substances [43, 44]. 

The few observations of nucleation in the free troposphere are consistent with binary sulfuric acid-water nucleation. In the boundary layer a third nucleating component or a totally different nucleation mechanism is clearly needed. Gaydos et al. (2005) showed that ternary sulfuric acid-ammonia-water nucleation can explain the new particle formation events in the northeastern United States through the year. These authors were able to reproduce the presence or lack of nucleation in practically all the days both during summer and winter that they examined (Figure 11.16). Ion-induced nucleation is expected to make a small contribution to the major nucleation events in the boundary layer because it is probably limited by the availability of ions (Laakso et al. 2002). Homogeneous nucleation of iodine oxide is the most likely explanation for the rapid formation of particles in coastal areas (Hoffmann et al. 2001). It appears that different nucleation processes are responsible for new particle formation in different parts of the atmosphere. Sulfuric acid is a major component of the nucleation growth process in most cases. 

---