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epa.gov/mapper/) which allows people to view data about the state of air quality and other environmental exposures where they live and to map them against demographic and socio-economic characteristics (Figure 2.1.8).
In Canada, the concept of critical loads has been used to assess and manage deposition of pollutants and their impact on ecosystems. A critical load is a rate of deposition at which harmful ecological effects are not anticipated and ecosystems damaged by past exposures may eventually recover. Figure 2.1.9 presents a new critical load map for acidifying deposition for Canada. In the US, land management agencies and researchers have begun to use critical loads to assess the cumulative impacts of nearby development and other stressors on ecosystems, but the
approach has not yet been accepted into official planning and regulatory development.
2.1.4 Developing trends
Urbanization Continued urbanization, or urban sprawl, is an important driver for air pollution and greenhouse gas emissions across North America. As urban areas spread over a landscape, there is more demand for transportation and energy, and an increase in the associated emissions. As land uses change, so does the population density and proximity to emissions sources, changing the patterns of exposure to air pollution.
Figure 2.1.9: Critical loads of acidity for lakes or upland forest soils across Canada