Source: Living in the Environment by Miller, G. Tyler; Spoolman, Scott.
Reproduced with permission of Cengage Learning via Copyright Clearance
Center
Figure 9.4 Steps in the formation of photochemical smogCATALYTIC CONVERTERS
A catalytic converter is an exhaust emission control device that converts toxic
chemicals in the exhaust of an internal-combustion engine into less noxious
substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction
in which noxious by-products of combustion are converted to less toxic
substances by way of catalyzed chemical reactions. Most present-day vehicles
that run on gasoline are fitted with a “three way” converter, since it converts the
three main pollutants:
(a) Reduction of nitrogen oxides to nitrogen and oxygen: NOx → O 2 + N 2(b) Oxidation of carbon monoxide to carbon dioxide: CO + O 2 → CO 2
(c) Oxidation of unburned hydrocarbons to carbon dioxide and water: CxH2x
+ O 2 → CO 2 + H 2 OAlthough catalytic converters are effective at removing hydrocarbons and
other harmful emissions, they do not reduce the emission of carbon dioxide
produced when fossil fuels are used for fuel. Additionally, the Environmental
Protection Agency (EPA) has stated that catalytic converters are a significant and
growing cause of global warming, because of their release of nitrous oxide
(N 2 O), a greenhouse gas over 300 times more potent than carbon dioxide. The
EPA states that motor vehicles contribute approximately 50% of nitrous oxide
emissions and nitrous oxide makes up 7% of greenhouse gases.
CASE STUDIES
DONORA, PENNSYLVANIA (1948): In 1948, industrial smog from the
local zinc and steel smelting plants settled in the valley where the town was
located, resulting in 20 deaths and over 7,000 people being hospitalized. This
incident resulted in the first meaningful federal and state laws to control air
pollution.