Atmospheric composition change – global and regional air quality
Introduction
“Clean air is considered to be a basic requirement of human health and well-being. However, air pollution continues to pose a significant threat to health worldwide” (WHO, 2005b).
Air pollution can be defined as “when gases or aerosol particles emitted anthropogenically, build up in concentrations sufficiently high to cause direct or indirect damage to plants, animals, other life forms, ecosystems, structures, or works of art” (Jacobson, 2002). The state of air pollution is often expressed as Air Quality (AQ). Air quality is a measure of the concentrations of gaseous pollutants and size or number of particulate matter. As previously stated air pollution has implications for a number of contemporary issues including:
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Human health, (e.g. respiratory, cancer, allergies…),
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Ecosystems (e.g. crop yields, loss of biodiversity),
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National heritage (e.g. buildings),
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Regional climate (aerosol and ozone exhibit a strong regionality in climate forcing).
Though air quality is a measure of the anthropogenic perturbation of the “natural” atmospheric state it has to be considered in the wider context of the interactions with biogenic and other natural emissions that may have feedbacks with atmospheric composition and climate.
The World Health Organization estimates that 2.4 million people die each year from causes directly attributable to air pollution, with 1.5 million of these deaths attributable to indoor air pollution (WHO, 2002). For example in the European Union, 21,400 premature deaths each year are associated with O3 while for particulate matter (PM) the average loss of life expectancy owing to exposure is estimated to be nine months (EEA, 2007) (see Fig. 1). Exposure to air pollutants is largely beyond the control of individuals and requires action by public authorities at the national, regional and even international levels.
Air pollution is not a modern issue and examples are available from antiquity and the middle ages (Jacobson, 2002, Stern, 1968). In modern times, interest in air quality issues rekindled when cities like Los Angeles began to experience noxious haze-like conditions (Haagen-Smit, 1952). The LA smog is often termed photochemical smog and is quite different in origin to the London smogs of the 19th and 20th centuries, which have their origins in abnormally high concentrations of smoke particles and sulphur dioxide. Though at the time photochemical smog was thought to be a relatively local phenomenon, with the understanding of its chemistry came the development of a photochemical oxidant theory for the whole of the troposphere (Chameides and Walker, 1973, Crutzen, 1973). The fundamentally shared chemical origin of air pollution across various spatio-temporal scales makes air quality both a local and global problem.
Over the last decade there has been a great deal of research on Air Quality and the control of atmospheric composition. The aim of this review is to summarize, overview and integrate the main research findings over the last five years in the area of air quality and health with an emphasis on the European context. This review builds on the extensive work covered in the International Global Atmospheric Chemistry Project (IGAC) synthesis (Brasseur et al., 2003). The review does not set out to provide comprehensive coverage to the topic area, which in itself is too large, but aims to summarize what in the authors, opinions are the key research findings and their implications. The authors have been drawn from the EU ACCENT network of excellence (http://www.accent-network.org). The review deals with the science that both contributes to our understanding and quantification at a processes level as well as integrating that understanding together in a model framework.
Tropospheric chemistry has the key steps of emission, chemical transformation, transport and deposition. This is shown, as an example, for VOCs in Fig. 2. Deposition at a process level is dealt with in the sister review (Fowler et al., 2009), measurement techniques in Laj et al (Laj et al., 2009) and chemistry–climate in Isaksen et al. (2009). The review first examines emissions of trace gases and particles into the atmosphere before moving on to gas phase and aerosol processing. There is a section on cross-cutting integrative themes that places the process view in the atmospheric context. An overview of major findings in the role of atmospheric transport on atmospheric composition is also given. The review concludes with a view of the policy and science implications of the last decade's work and a consideration of future perspectives.
Section snippets
Trace gases and aerosol emissions
Trace gases are produced by physical, biological and chemical processes on land and in the oceans. The natural cycles include emissions of a large variety of chemical species, which have been perturbed over the past decades by human activities, such as agriculture and deforestation. Fossil fuel extraction and burning, energy production and consumption, industrial activities, transportation and landfills have also led to the emissions of large quantities of pollutants into the atmosphere. This
Ozone and its precursors
The following section reviews new discoveries in the area of gas phase atmospheric processing in the context of air quality. It deals with key oxidant precursors in terms of hydrocarbons and NOx as well as ozone itself. A further section looks at new discoveries in radical chemistry, key intermediates in atmospheric photochemistry.
The impact of atmospheric transport on composition
In order to establish the source–receptor relationships of air pollutants it is important to consider atmospheric transport processes and the chemical conversions and deposition processes occurring enroute across all the spatial scales. Depending on the lifetime and properties of a pollutant, it can be transported on scales ranging from the street level to the global scale. As the processes controlling the transport are scale-dependent, this chapter is structured according to the scales and
Conclusions and future perspectives
This section attempts to draw out some of the more important policy-related conclusions from the work described in the previous sections. In particular, it consolidates the implications of the earlier sections for policy and strategy as well as looking forward to the implications of climate change for air quality.
Acknowledgements
The authors would like to thank the EU ACCENT project. We would also like to thank Laura Dini and the ACCENT project office for the logistical support in assembling this review.
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