Sulphate aerosols

Apart from NO, ammonia also occurs in the atmosphere which is largely formed by the natural ecosystem. In industrial regions it can undergo a series of reactions to produce ammonium sulphate aerosol in presence of sulphuric acid, or alternatively form NH2, N2O and NO. These species are responsible for the destruction of ozone in the troposphere9. 

Erie, F., A. Grendel, D. Perner, U. Platt, and K. Pfeilsticker, Evidence of Heterogeneous Bromine Chemistry on Cold Stratospheric Sulphate Aerosols, Geophys. Res. Lett., 25, 4329-4332 (1998). 

Randeniya, L. K., P. F. Vohralik, I. C. Plumb, K. R. Ryan, and S. L. Baughcum, Impact of the Heterogeneous Hydrolysis of BrONOj on Calculated Ozone Changes Due to HSCT Aircraft and Increased Sulphate Aerosol Levels, Geophys. Res. Lett., 23, 343-346 (1996a). 

Jones, A., D. L. Roberts, and A. Slingo, A Climate Model Study of Indirect Radiative Forcing by Anthropogenic Sulphate Aerosols, Nature, 370, 450-453 (1994). 

Langner, J., H. Rodhe, P. J. Crutzen, and P. Zimmermann, Anthropogenic Influence on the Distribution of Tropospheric Sulphate Aerosol, Nature, 359, 712-716 (1992). 

The Mediterranean Basin is highly influenced by shipping emissions due to its extremely busy shipping routes. These emissions may account for 2 1% of the mean annual ambient air PM10 levels (25% primary particles and 75% secondary particles) and for 14% of the mean annual PM2.5 in Mediterranean urban areas [51]. It has been estimated that 54% of the total sulphate aerosol column burden over the Mediterranean in summer originates from ship emissions [52],... 

The mechanism of deposition in the size range 0.1-1 /tm, and the appropriate vg values, have been the subject of some dispute. Sulphate particles in the urban and suburban atmosphere have median diameters of about 0.5 /um (Heard Wiffin, 1969 Whitby, 1978). Using the results of Fig. 6.9, and weighting vg according to the mass of sulphate in various size ranges, Garland (1978) calculated a mean value of vg for sulphate aerosol of 1.0 mm s-1. Nicholson Davies (1987) measured the profile of SO4- concentrations, and also wind speed, above agricul-... 

Dimethyl sulphide is the most dominant of the reduced sulphur gas found in surface layers of the ocean (Lovelock et al. 1972). The emission of dimethyl sulphide from seawater is expected to balance the excess sulphur deposition over the remote oceans (Charlson et al. 1992). Charlson et al. (1987) proposed a hypothesis, known as the CLAW (after the authors Charlson, Lovelock, Andreae and Warren) hypothesis connecting biogenic DMS emissions to changes in albedo, in which increased production of DMS due to global warming is expected to lead to more sulphate aerosols and subsequently to more cloud condensation nuclei (CCN) that in turn enhances back radiation. 

Penner JE et al (1998) Climate forcing by carbonaceous and sulphate aerosols. Cllm Dyn 14 839-851... 

Aerosol phase simulations. Atmos Environ 31 587-608 Jones A, Roberts DL, Slingo A (1994) A climate model study of indirect radiative forcing by anthropogenic sulphate aerosols. Nature 370 450 53... 

It appeared that contribution of other emissions besides sulphates to this particular event was negligible. Thus, only the measured aerosol below 1 pm size limit (typical for sulphate aerosol) was taken for comparison. 

Sulphate aerosol production, which is by far the most important process, changes however noticeably under different atmospheric conditions... 

Fig. 1. Relative importance of various urban sulphate aerosol production mechanisms T = total sulfate A = H2SO4 condensation H = HjOj oxidation O = uncatalyzed oxygen oxidation Q = O3 oxidation F = iron catalyzed oxidation M = manganese catalyzed oxidation C = soot catalyzed oxidation.

Allen A. G., Oppenheimer C., Perm M., Baxter P. J., Horrocks L., Galle B., McGonigle A. J. S., and Duffell H. J. (2002) Primary sulphate aerosol and associated emissions from Masaya volcano, Nicaragua. J. Geophys. Res. (4), Doi 1O.1O29/20O2JDO (4 December 2002). 

Boucher O., Moulin C., Belviso S., Aumont O., Bopp L., Cosme E., von Kuhlmann R., Lawrence C. G., Pham M., Redyy M. S., Sciare J., and Venkataraman C. (2002) Sensitivity study of dimethylsulphide (DMS) atmospheric concentrations and sulphate aerosol indirect radiative forcing to the DMS source representation and oxidation. Atmos. Chem. Phys. Discuss. 2, 1181-1216. 

Prospero, J.M., Savoie, D.L., Saltzman, E.S. and Larsen, R.J., Impact of oceanic sources of biogenic sulphur on sulphate aerosol concentrations at Mawson, Antarctica. Nature, 350 (1991) 221-223. 

Sulphur dioxide takes part in chemical reactions with substances naturally present in the atmosphere and with other pollutants, some of them driven by sunlight and others by the presence of cloud droplets. The end product of the oxidation of sulphur dioxide is sulphuric acid, together with ammonium sulphate, in the form of suspended particles. These sulphur particles, known collectively as sulphate aerosol, tend not to be removed particularly efficiently by dry deposition and have timescales limited only by the scavenging during rain events. Sulphate aerosols may have lifetimes up to 10 days and may travel hundreds and thousands of kilometres before encountering rain. The capture of sulphate aerosol by rain leads to the process of wet deposition and this process accounts for the remaining one third of the total removal of sulphur species. 

Fig. 7.22 Modelled geographical distribution of annual direct radiative forcing (Wm 2) from anthropogenic sulphate aerosols in the troposphere. The negative forcing is largest over, or close to, regions of industrial activity. After IPCC (1995). With permission of the Intergovernmental Panel on Climate Change.

Trapping of aerosol particles. Falling snow efficiently scavenges particles suspended in air. " Wind blowing over snow also deposits particles within the snow, that acts as an efficient filter. The fate of these particles is not well known. Hydrophilic particles such as sulphate aerosols may interact with the snow and spread on the surface, but this is not documented. Some particles remain essentially unaffected, as observed by SEM and just sit on the surface of snow crystals. 

During the background period before the volcano eruption, the SA was formed in the stratosphere due to the photo-oxidation of stratospheric SO2, and the coefficient of correlation between the SA and GCO was negative (r=-0.46 0.17, with P=0.95). When products of the volcano eruption came to our latitudes, O3 was absorbed in the sulphate aerosol during formation of SA from SO2 (from June 1993 to Febraary 1993), so the concentration of O3 was reduced. Thus the negative correlation between SA and GCO increased comparing to the background period r=-0.76 0.12, P=0.99. 

Figure 13. Growth curves for sulphuric acid droplets r, equilibrium radius ro, initial radius X0 initial concentration of sulphuric acid. Reprinted from Journal of Aerosol Science, 13, AT Cocks and RP Fernando, The growth of sulphate aerosols in the human airways, pp. 9-19, 1982, with kind permission from Elsevier Science Ltd...

Figure 15. The influence of inhaled particle size and breathing mode on ammonium sulphate aerosol deposition (—) non-hygroscopic particle behaviour included for comparison minute volume = 30 1. RH = relative humidity Reproduced with permission from Martonen TB (1985). Ambient sulphate deposition in man modelling the influence of hygroscopicity. Environmental Health Perspectives, 63, 11-24...

Cocks AT and Fernando AP (1982). The growth of sulphate aerosols in the human airways. J Aerosol Sci, 13, 9-19. 

Larson TV, Covert DS, Frank R et al. (1977). Ammonia in the human airways neutralization of inspired acid sulphate aerosols. Science, 197, 161— 163. 

Martonen TB, Barnett AE and Miller LJ (1985). Ambient sulphate aerosol deposition in man modelling the influence of hygroscopicity. Environ Health Perspect, 63, 11-24. 

Toumi, R., S. Bekki, and R. Cox, A model study of ATMOS observations and the heterogeneous loss of N2O5 by the sulphate aerosol layer. J Atmos Chem 16, 135, 1993. 

Roberts, D. L. (1996) Sulphate aerosol modelling at the Hadley Centre, presented at ACACIA Sulfate Aerosol Research Project Planing Meeting, National Center for Atmospheric Research, Boulder, CO, Feb. 27-28. 

Harrison, R. M. and A.-M. N. Kitto (1992) Estimation of the rate constant for the reaction of acid sulphate aerosol with NH3 gas from atmospheric measurements. Journal of Atmospheric Chemistry 15, 133-143... 

Sulphate aerosols scatter the light very strongly this has the effect not only of reducing the visibility but also of increasing the albedo of the atmosphere, i.e. its power to reflect the sun s rays these aerosols therefore contribute, like other particles, to cooling the planet and counterbalancing the greenhouse effect. 

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