Page 121 - Fundamentals of Air Pollution

IV. Mobile Sources 91

IV. MOBILE SOURCES
A mobile source of air pollution can be defined as one capable of moving
from one place to another under its own power. According to this definition,
an automobile is a mobile source and a portable asphalt batching plant is
not. Generally, mobile sources imply transportation, but sources such as
construction equipment, gasoline-powered lawn mowers, and gasoline-
powered tools are included in this category.
Mobile sources therefore consist of many different types of vehicles,
powered by engines using different cycles, fueled by a variety of products,
and emitting varying amounts of both simple and complex pollutants. Table
6-4 includes the more common mobile sources.
The predominant mobile air pollution source in all industrialized coun-
tries of the world is the automobile, powered by a four-stroke cycle (Otto
cycle) engine and using gasoline as the fuel. In the United States, over 85
million automobiles were in use in 1990. If the 15 million gasoline-powered
trucks and buses and the 4 million motorcycles are included, the United
States total exceeds 100 million vehicles. The engine used to power these
millions of vehicles has been said to be the most highly engineered machine
of the century. When one considers the present reliability, cost, and life
expectancy of the internal combustion engine, it is not difficult to see
why it has remained so popular. A modern automotive engine traveling
8
100,000 km will have about 2.5 x 10 power cycles.
The emissions from a gasoline-powered vehicle come from many sources.
Figure 6-12 illustrates what might be expected from an uncontrolled (1960
model) automobile and a controlled (1983 or later model) automobile if it
complies with the 1983 federal standards (7). With most of today's auto-
mobiles using unleaded gasoline, lead emissions are no longer a major
concern,

TABLE 6-4
Emissions from Mobile Sources
Power plant type Fuel Major emissions Vehicle type
Otto cycle Gasoline HC, CO, CO 2, NO X Auto, truck, bus, aircraft,
marine, motorcycle, tractor
Two-stroke cycle Gasoline HC, CO, CO 2, NO,, Motorcycle, outboard motor
particulate
Diesel Diesel oil NOj, particulate, SO,, CO 2 Auto, truck, bus, railroad,
marine, tractor
Gas turbine (jet) Turbine NO*, particulate, CO 2 Aircraft, marine, railroad
Steam Oil, coal NO r, SO*, particulate, CO 2 Marine