Table of Contents
Earth’s atmosphere contains various gases and aerosol particles (see Chapter 1). Detailed description about the cycles of some important components can be found in other chapters (carbon compound: Chapter 5, nitrogen compounds: Chapter 6, sulphur compounds: Chapter 7, ozone: chapter 8, aerosol particles: Chapter 9). The atmospheric transport processes of air pollutants (Chapter 10), as well as chemical reactions (Chapter 4) and deposition processes (Chapter 12) are also described in detail hereinafter. This chapter present the main source types of air pollutants and their key features.
During air pollution, different gases, particulates or biological materials get to the atmosphere from various natural and anthropogenic sources and modify its natural composition. Emissions influenced by weather conditions, a number of physical and chemical properties and, in case of anthropogenic sources also by technological parameters. The emitted amounts vary with respect to the location and time. Pollutants emitted to the atmosphere can be transported from emission sources to even a long distance (transmission) in the function of their properties and weather conditions. In the atmosphere, complex chemical reaction processes can be realized which can produce secondary air pollutants. After these processes, air pollutants can be removed from the atmosphere by chemical reactions, dry or wet deposition (Figure 2.1).
Atmospheric air pollutants have several effects on the environment in the atmosphere and after they remove into the different surfaces. The chemical composition of the atmosphere can influence both the weather condition and the climate (e.g. cloud formation, visibility, radiation budget). Various air pollutants emitted into the atmosphere by both natural and human activities are the cause of many current and potential environmental problems, such as acidification, air quality degradation (Figure 2.2), global warming/climate change, stratospheric ozone depletion, harmful effects on vegetation, soils, ground water, aquatic ecosystems, human health and also on built environment (further information about the effects of air pollutants can be seen in Chapter 13 and Chapter 14).
There are many different types of sources of atmospheric emissions, for example industry, energy supply (power plants, refineries, incinerators, factories, fossil fuel extraction and production sites, etc.) transport, animals and humans, agricultural activities, natural and managed vegetations, soil etc (EEA Technical report, 2009).
Due to the high variability and complexity of emission sources, it is not possible to measure emissions from all the different source types. In practice, atmospheric emissions are generally estimate based on measurements made at selected or representative samples of the (main) sources and source types. These estimated emissions are collected into emission inventories. Emissions inventories may contain three main types of sources, namely point, area and line sources. However, in some cases the emission inventories refer to a specific area (e.g. to a country or a region).
Three main types of emission sources are the following:
Point source: a single, fixed point, from were air pollutants can be emitted into the atmosphere continuously or instantaneously (for example during an accidental release). Typical example for point source is a smokestack.
Area source: emission of air pollutants from a specific area (e.g. from a city, or from a forest fire). In emission inventories, area sources can refer to an administrative area, such as a country, or region, or for a regular grid, (e.g. 50 km × 50 km grid in EMEP emission inventories: http://www.ceip.at/ceip/, or other derived grid: see Figure 2.3).
Line source: generally refers to emissions from transport (vehicle emissions from road transport, railways, shipping or aviation) along a line of the road, railway-track, sea-lane etc.
The primary sources of atmospheric pollutants could be classified as natural or anthropogenic sources. During natural processes the atmosphere interacts continuously with other spheres (e.g. biosphere, lithosphere, hydrosphere), and these spheres can be both sources and sinks of atmospheric components. This quasi steady state is disrupted by human activities. Anthropogenic emissions are mainly related to energy and food supply of world population.