Block 8: Environmental Issues and Public Health - Air Pollution Chapter 4: The Principal Sources Of The Common Air Pollutants; Methods Of Estimating Emission Rates

The principal sources of the common air pollutants:

Ambient air pollutant concentrations are the result of the interaction of pollutant emissions, chemical and physical transformations, dispersion of the pollutants and pollutant deposition. There are natural and ‘anthropogenic’ (the result of human activities) sources of pollution. Dispersion of pollutants is greatly influenced by meteorology, mainly wind speed and direction, and vertical air movement. The oceans and surfaces of plants, the earth’s surface and buildings act as pollutant sinks

The sources of air pollution may be classified as stationary point sources (generally industrial in origin), diffuse or area sources and mobile sources (mainly cars and trucks). The stationary industrial sources are usually classified by process type or sub-type. Thus an oil refining plant also includes large industrial boilers as a sub-type. Small and medium scale plants such as garment or food processing plants may include industrial boilers, a common source of air pollution. The quality and type of fuel used for energy production are important determinants of the air pollution potential of a plant. Each type of plant or activity generally emits more than one pollutant, and the pollutant emission rate depends on the fuel type and quality, the design of the plant (and whether fitted with air pollution control devices or not), and the activity rate or rate of fuel use or production rate of the plant.

Table 4.1 lists some generic stationary sources and typical pollutants emitted by these sources (the list is by no means complete. Depending on the classification system, stationary sources may be classified into 50 to 100 different categories. South African regulations, for example, list of about 70 "Scheduled Industries".

Source apportionment data:

Ambient air quality in a given geographical region is influenced not only by the emission rates of various pollutants, by factors such a meteorology and local topography (mountains and other geographical features). The area influenced by local air pollution may be called an airshed. In order to develop an effective pollution management plan in a given region, a knowledge of the relative contribution of each source or group of sources to total emissions of a pollutant in the airshed is required. A single pollutant (SO₂ for example) may have a number of sources. Figure 4.1 below is a source apportionment graphic.

Figure 4.1: Source apportionment example for the common air pollutants

It is important to note that the relative contribution of different sources (the source apportionment) to the total emissions of a particular pollutant may vary considerably from city to city within a country, and from country to country. In the example above the major SO₂ source is an electric power station. But in a city or an urban area without a local power station (such as Durban) electric power generation would not be a significant SO₂ source.

In the South Durban region the main SO2 sources are the two oil refineries - together they contribute more than 50% to the regional SO2 inventory. The results (for SO2 emissions) of an emission inventory study in the South Durban Industrial Area are shown in Figure 4.2.
	Figure 4.2: SO2 source apportionment, South Durban
	Emission Inventory for South Durban, Ecoserv (Pty) (Ltd), 2000

The city-to-city variability of pollutant emmision rates is illustrated by the following data (Table 4.2)