Chevrolet TrailBlazer, Руководство по обслуживанию, Страница: 205 / 677

The Clean Air Act Amendments of 1990 recognized the fact that vehicles with
malfunctioning emissions control systems could go undetected for extended periods.
Annual emissions inspection programs were not enough. The EPA required vehicle
manufacturers to produce vehicle OBD systems capable of immediately identifying the
vehicle operator of emissions faults, effective from 1996. As part of the OBD II system, all
emissions-related components would be monitored for malfunction or deterioration.
On today's new vehicles, HC and CO emissions are reduced by more than 95% when
compared to a 1960's vintage vehicle; NO
X
emissions are reduced by 90%.
The exhaust emissions of automotive engines contain a number of harmful pollutants. In
order to minimize the amount of harmful pollutants being produced, manufacturers have
developed automotive emissions controls. The following is a list of the harmful exhaust
gases manufacturers plan to reduce, which includes how the gases are formed and why
they are dangerous.
Carbon Monoxide (CO)
Consists of carbon & oxygen. This colorless, odorless, poisonous gas is the product of
incomplete combustion. By weight, carbon monoxide accounts for the 47% of air pollution.
Hydrocarbon (HC)
Hydrocarbons consist of carbon and hydrogen. Hydrocarbons are emitted in an unburned
form from equipment which uses a petroleum product as a source of fuel. Hydrocarbons
are one of the key elements responsible for the production of photochemical smog.
Oxides of Nitrogen (NO
X
)
Oxides of nitrogen consist of nitrogen combined with varying amounts of oxygen. NO
X
are
produced by heat and pressure during the combustion process. NO
X
are also a main
component in smog.
Photochemical Smog
Photochemical smog, commonly referred to simply as smog, is a by-product of the
combination of HC and NO
X
. In the presence of sunlight these two elements form ozone
(O
3
), nitrogen dioxide, and nitrogen nitrate; all of which cause respiratory problems.
Nitrogen dioxide is a light brown colored gas which can affect visibility in the air corridors
around major airport terminals and above highways.
Particulates
Particulates are tiny particles of liquids and solids which are dispersed into the atmosphere
during any burning process. Particulates are composed of carbon, ash, oil, grease, and
metal oxides. Smoke, haze, and dust are types of air pollution which are readily visible and
are known to complicate respiratory problems cause by smog.