The sulphur cycle and atmospheric acidity

The S02 from either source exists in the atmosphere either as a gas or dissolved in rain and cloud droplets, whose pH it lowers due to the acidity of the gas. However, within water drops S02 can be quite rapidly oxidized to form sulphuric acid (H2S04), which makes them much more acidic since H2S04 is a strong acid (see Box 3.8). MSA formed by oxidation of DMS, via the OH/NO3 addition route (Fig. 7.18), also contributes to the acidity of atmospheric water. Since this 

The mass balance for sulphur in Fig. 7.17b represents the various fluxes integrated over the whole globe. Because all the different sulphur compounds shown in Fig. 7.18 have atmospheric residence times (see Section 3.3) of only a few days and so are not well mixed, their distributions in the air are often inhomogeneous. Indeed, for any particular region of the atmosphere, it is likely that one of the major sulphur sources will dominate and thence determine the acidity of rain and aerosols. In general, for remote—particularly marine—areas, the DMS-S02-SOj route is likely to control, whereas close to urbanized/industrialized land, 

In Fig. 7.19 atmospheric measurements of particulate MSA, SO4 (after subtraction of the component coming from sea salt, the so-called non-sea-salt-sulphate (nss-SO )) and NHJ made in air at Mawson in Antarctica are shown. This site is very remote from human activities and typically receives air which has blown over thousands of kilometres of the Southern Ocean before being 

If a sample collected in the environment (aerosol, rain, surface water) has a 834S value of +20%o CDT, then it should have its sulphur essentially from the 

2 The delta notation for expressing stable isotope ratio values 

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