State Indicators

Ozone layer

The stratospheric thinning of the ozone layer occurs worldwide: to a lesser extent near the equator and increases with latitude toward the poles, especially to the south; in Latin America, its most important effects are observed in countries like Argentina, Chile, Brazil and Uruguay (WMO et al., 2007). The most obvious evidence of this thinning occurs in Antarctica, where the so-called "ozone hole" appears every year due to the local weather conditions leading to the formation of polar stratospheric clouds (ice clouds) and the isolation of the polar wind, which favor the increase of ozone-depleting reactions (WMO et al., 2007; NASA, 2009). The indicator Stratospheric ozone concentration: global, over Antarctica and over two Mexican cities reflects three different perspectives of the same issue: the global thickness of the ozone layer is a general measure for the entire planet, the thickness over the Antarctica is the worst-case scenario of the problem and, finally, measurements for two Mexican cities will enable to assess the occurrence of this problem in Mexico. Environment Canada and OECD include global stratospheric ozone indicators, as well as for selected cities (OECD, 2005; Environment Canada, 2003).

Atmospheric ODS concentration

ODS accumulate in the lower atmosphere as nonreactive gases, but when they reach the stratosphere, UV light triggers chemical reactions that transform them into reactive ozone-depleting gases (WMO et al., 2007). The impact of ODS depends on both their quantity and stability in the atmosphere, as well as on their ozone-depleting potential (WMO et al., 2007; NASA, 2009). The indicator Global atmospheric concentration of ozone-depleting substances shows the potential impact on the ozone layer derived from the consumption of these substances. The US-EPA uses an indicator of ODS concentration (EPA, 2008), while the OECD’s and Environment Canada’s initiatives (Environment Canada, 2003; OECD, 2005) use the atmospheric CFCs concentration.