Clean air is an important prerequisite for sustainable growth and is a basic requirement for human health and welfare.  Air quality also impacts the natural environment; increased air pollution causes stress to aquatic and terrestrial ecosystems, and contibutes to acidification and global climate change.  These impacts, in turn, affect crop activity, forest growth, biodiversity and aesthetics.

Despite improvements in air quality over the last 30 years, smog continues to be a serious problem in southern Ontario cities, and particularly in the GTA.  Urban pollutants arise from a variety of sources, but are mainly related to combustion processes including vehicle use and energy consumption.

The clean air component of STEP addresses technologies that help reduce emissions of pollutants to the atmosphere and prevent smog-related heat build-up in urban environments.