Urbanization and the Geoenvironment - Sustainable Practices in Geoenvironmental Engineering - page 224

trafic areas. Pedestrians or passengers in vehicles that do not stay in the area long will not
be affected but there could be signiicant impacts for those that live in the area. Carbon
monoxide is a major contaminant from vehicles. In particular, intersections where vehicles
are stationary for a period can substantially increase the level of carbon monoxide (CO)
released into the air. In general, although in the streets of large European cities, 8-h average
carbon monoxide concentrations are lower than 20 mg/m 3 (17 ppm) with brief increases
to around 60 mg/m 3 (53 ppm) (WHO Regional Ofice for Europe, Copenhagen, Denmark,
2000). The most prevalent air contaminants from vehicular emissions are nitrogen oxides
(NO x ), hydrocarbons, and CO.
In the past, lead in gasoline led to accumulation of lead on surface soils for many years.
Page and Ganje (1970) showed that 15 to 36 μg/g over a period of 40 years accumulated in
high trafic areas compared with negligible amounts in low trafic areas. Although lead in
gasoline has been eliminated in many countries, the low mobility of lead ensures that the
lead remains in the ground as a contaminant for many years.
In terms of grams of emissions per mile, for the period from 1996 to 2003, emissions of
(a) hydrocarbons were 0.25 g/mile, (b) CO, 3.4 g/mile, and (c) nitrogen oxides, 0.4 g/mile
(USEPA, 1993). Although emissions have decreased substantially over the years, the com-
bination of poorly maintained cars together with more cars and other types of heavy duty
vehicles that consume more gasoline and emit higher emissions (such as sports utility
vehicles, light trucks, vans, and pickup trucks) ensure that reduction in noxious emission
will not be readily accomplished. Not only do vehicles emit various contaminants, they
also contribute over 20% of the carbon dioxide emissions from gasoline. Other petroleum
fuels add another 12%. Reduction in vehicle use or the use of alternate fuels or other means
will be required to substantially reduce the emission of this greenhouse gas. Without
entering into the lively debate on global warming and climate change and (a) human fac-
tors causing such changes, (b) reliability of available data, (c) how far back in time one
needs for data scrutiny, and (d) viability and applicability of climate change models, it is
pertinent to note that the accumulation of greenhouse gases will contribute to other factors
that are responsible for climate change.
Paved road surfaces share the same problems as covered impervious areas in cities;
rain water cannot iniltrate into the soil but will accumulate on roads and will wash away
the contaminants on the streets. This can include motor oil, grease, antifreeze, metals,
phosphorus, and other contaminants that classify as pollutants. These are then washed
into local waterways and rivers by streaming lows, resulting in oxygen depletion and
contamination of the waters, killing ish, plants, and other aquatic life. Public health is
threatened when the contaminated water and contaminated ish are ingested.
Soil quality is another issue of importance. Air particulates (contaminants) are depos-
ited on the ground from precipitation passing through the airborne particulates. These
will ind their way onto surface soils and into the subsoil and also into rivers and ground-
water. Human exposure with the particulates can be through inhalation, contact with the
soil, ingestion of water and crops grown in contaminated soil. Ingestion of vegetables
grown in urban gardens and children playing in exposed sand boxes and bare soil land-
scape are good examples of human exposure to deposited air particulates that classify
as contaminants/pollutants. Although awareness of the potential hazards of such a form
of water and soil contamination exists, the same cannot be said for information and data
on contaminant concentrations and distributions from such types of deposited airborne
particulates.
Soils and sediments contiguous to roads can exhibit high levels of contamination. In
Germany, levels of lead, cadmium, chromium, nickel, vanadium, and zinc in soils near