Geography Reference
In-Depth Information
Asphalt, concrete and other hard materials that dominate city surfaces have rather high ca-
pacities to absorb solar energy, causing urban areas to warm up much faster than countryside.
Heat is a by-product of motors and machines, which abound in cities. Ironically, air condi-
tioners are a major contributor to urban heat islands during summer.
Exhaust from automobiles and engines is warm in and of itself, but also has high concen-
trations of gases that absorb and retain solar energy with great efficiency.
Dust domes and smog
Exhaust from internal combustion engines and other sources is high in particulate matter and smog-
producing chemicals. As a result, air pollution problems, attendant to resulting
dust domes
and
smog,
tend to be particularly acute in urban areas, as manifested in part by disproportionately high rates of
asthma and other respiratory problems. The flip side of sorts is that dust particles serve as the focus
for condensation, leading to production of rain. Thus, urban areas tend to have higher precipitation
rates than neighboring rural areas, the rainfall “flushing” the heat and smog from the atmosphere and
providing temporary relief from the heat island effect.
The extent of dust domes and smog vary from city to city, and not simply as a function of sizes. Ter-
rain may be a factor. Mexico City and Los Angeles, for example, occupy low-lying lands that are
surrounded and partially surrounded respectively by high hills and mountains that contain and con-
centrate air pollution. Existence and enforcement of environmental law, particularly as it relates to
engine emissions, is also a factor.
Finding a place for refuse
Large cities produce large quantities of refuse and sewage and have few solutions regarding their
safe disposal. Pursuant to passage of environmental protection laws, ocean dumping is no longer
an option, and many cities are running out of sites for landfills within their boundaries. One of the
more provocative consequences has been substantial interstate commerce in refuse, in which typic-
ally a poor rural county agrees (for a price) to serve as the final resting place for big-city garbage and
sewage. Increased use of efficient, high-tech incinerators within cities themselves may be the way of
the future, provided they comply with environmental protection laws designed to promote clean air.
Even if that happens, however, the contribution of this technology to dust domes, smog, and urban
heat islands will be measurable.
