Sulfur compounds

3.6.1 Introduction

Sulfur compounds are very important atmospheric constituents, since in clean tropospheric air as well as in the stratosphere the majority of aerosol particles are composed of ammonium sulfate or sulfuric acid (see Chapter 4). This finding is particularly interesting since with the exception of sea salt sulfur, a predominant portion of sulfur emission is in gaseous form.

The study of the atmospheric sulfur cycle is a rapidly expanding field because human activity provides an important sulfur dioxide source. In the atmosphere S02 is converted to sulfate containing aerosol particles which can modify the radiation balance of the Earth-atmosphere system, the optical properties and the precipitation forming ability24 of the air.

3.6l2 Origin of atmospheric sulfui

Sulfur compounds in the atmosphere are provided by the decomposition of organic matter, combustion of fossil fuels, production of sea salt particles and volcanic activity. We can rather well quantify the strength of these sources, except the intensity of biological sulfur production.

23 If the role of lightning in NOA production is significant the value of the biological source strength is less.

24 By acting as condensation nuclei. It is well documented (e.g. Twomey. 1971) that atmospheric condensation nuclei consist mainly of ammonium sulfate.

The emission rate of anthropogenic sulfur dioxide (95 % of sulfur due to pollution sources is S02) was estimated by Katz(see Kellogg et at.. 1972) to be 77 x1061yr"1 in 1943. According to more recent estimates (Friend, 1973) 130xl06t of anthropogenic S02 is released into the atmosphere annually. Comparison of the two figures makes it evident that during about two or three decades the emission increased by a factor of 1.7. This huge quantity of S02 is mainly due to combustion of fossil fuels containing sulfur. However, the effect of some industrial processes has also to be taken into consideration (Table 11). It is believed that the increase of S02 emission will continue in the future. Kellogg et al. (1972) speculate that the source strength will be 300 x 106 t yr"1 in 2000.

Table 11

Strength of different global anthropogenic S02 sources according to Friend (1973)

Table 11

Strength of different global anthropogenic S02 sources according to Friend (1973)

Source

Emission rale [10' 1 yr ']

Relative emission [/.,]

Coal-burning

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