Changes in Air
activities release a wide range of emissions into the environment
including carbon dioxide, carbon monoxide, ozone, sulfur oxides,
nitrogen oxides, lead, and many other pollutants. Some of these
emissions are toxic and have claimed many lives in some cities when
concentrations reached dangerous levels as in the "killer smogs"
of London in the 1950s and 1960s. Others emissions such as carbon
dioxide, act to trap heat in cities. Cities also release quantities
of dust into the atmosphere, with effects like those mentioned next.