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Industrialization, rapid population growth and consumption patterns are all factors that have led to overexploitation of natural resources and environmental degradation (UNEP, 2007). A clear example is the atmospheric issues currently occurring throughout the world. Among them, the most important ones in terms of their effects on population health and natural ecosystems are: declining air quality, climate change, and the degradation or depletion of the stratospheric ozone layer (UNEP, 2003; PNUMA, 2007).

Mexico currently faces air-pollution issues in its major metropolitan zones, with Mexico City as the most well known and documented example of air quality impairment (Lacasaña-Navarro et al., 1999; SEMARNAT, 2008). Additionally, we are now facing the global effects of climate change (IPCC, 2007) and contribute to emissions of the so-called greenhouse gases (GHGs) and substances that deplete the stratospheric ozone layer (ODS) although, in the latter case, the most obvious effects are not expressed in our country but at higher latitudes (PNUMA, 2003).

To understand and address this issue information on causal factors (pollutant emissions); the condition of the atmosphere, in terms of changes from its natural condition; and measures taken and their effects on solving specific problems is required.

The atmosphere acts as a protective layer by regulating the Earth’s temperature and preventing the entry of harmful solar radiation, such as UV radiation. Its natural composition includes mostly nitrogen (N2), oxygen (O2) and argon (Ar), but also other gases at lower concentrations, such as water vapor (H2O), ozone (O3), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) (NASA, 2004). However, this composition has been altered as a result of human activities, and other compounds have also been added which were not previously present (IPCC, 2007).

Pollutant emissions impair air quality and damage human health and ecosystems (Lacasaña-Navarro et al., 1999; Rosales-Castillo et al., 2001; WB, 2002; PNUMA, 2003). The main pollutants affecting air quality, named criteria pollutants, are sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide (NO2), particulate matter, ozone (O3) and lead (Pb) (INE-Semarnat, 2007). Other pollutants released to the atmosphere, known as greenhouse gases, are important for their effects on climate change: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) (IPCC, 2007).

As a result of human activities, the so-called ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and halons are also emitted to the atmosphere. These substances contain chlorine and bromine atoms, which destroy the stratospheric ozone that protects the Earth from UV radiation, harmful for living organisms (WMO, 2007).

Some of the compounds emitted have multiple effects and contribute to various atmospheric pollution issues. For example, sulfur dioxide produced by industrial processes and during combustion of sulfur-containing fuels impairs air quality (EPA, 2004; INE-Semarnat, 2007) and is also considered a greenhouse gas (IPCC, 2007). Also, CFCs (used as coolants, solvents and in the manufacture of polyurethane foam containers), HCFCs (substitutes for CFCs) and halons (used as fire-extinguishing agents) are considered ODS (WMO, 2007) and greenhouse gases (GHGs) at the same time (IPCC, 2007).

Due to the characteristics of pollutants, atmospheric issues have effects at different levels. Air quality deterioration is considered a local problem, since it primarily affects cities, but can become a regional problem affecting neighboring areas due to the dispersion of pollutants (e. g. transboundary pollution; UNEP, 2003). In contrast, global warming affects climate worldwide (IPCC, 2007). Although stratospheric ozone depletion is a problem involving all countries, its impacts are regional and are seen mainly over Antarctica, where the so-called "ozone hole" appears; in Latin America, its effects are seen mainly in Argentina, Chile, Brazil and Uruguay (PNUMA, 2003; WMO, 2007).

It is clear that atmospheric issues are complex, emission sources are diverse and pollutants act at different levels. There are programs and agreements currently in place for monitoring air quality, climate change and stratospheric ozone. The latter two are part of international agreements such as the United Nations Framework Convention on Climate Change and the Convention for the Protection of the Ozone Layer. This chapter presents indicators that describe the state of the atmosphere both locally and globally, as well as the pressures imposed on it and the measures taken to protect it and halt, reverse and mitigate its deterioration. The chapter addresses the air quality, climate change and stratospheric ozone subjects separately.




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INE-Semarnat. Tercer almanaque de datos y tendencias de la calidad del aire en nueve ciudades mexicanas. México. 2007. 

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Lacasaña-Navarro M., C. Aguilar-Garduño y I. Romieu. Evolución de la contaminación del aire e impacto de los programas de control en tres megaciudades de América Latina. Salud Pública de México.
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WMO. Scientific assessment of ozone depletion: 2006, Global ozone research and monitoring project—report núm. 50. Switzerland. 2007.