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Tech Corner

Auto Emissions and Solutions Part I – submitted by Rich Weiss
Assembled from various sources

In the 1960s, motor vehicles were identified as one of the primary sources of air pollutants in urban areas. Emission
standards for passenger cars were first imposed in California in 1965. These were followed by U.S. federal standards in
1968. The 1970 Clean Air Act further imposed stringent HC, CO, and NO reductions for 1975 and 1976. These reductions
were subsequently delayed and changed by the 1974 Energy and Environmental Coordination Act and the 1977 Clean Air
Act Amendments. Recognition of the motor vehicle as a major source of pollutants has spread to other countries, of which
many have imposed diverse standards and test procedures reflecting various degrees of stringency. The differences have
come about because of different regulatory philosophies and air quality goals, in combination with concerns about the
conflicting goal of improved fuel efficiency (Barnes and Donohue 1985).

Contaminants from gasoline-powered vehicles are discharged from the following sources:

Exhaust

This is the principal source and comprises the compounds exhausted from the engine. Numerous contaminants are present
in exhaust gases-—a variety of hydrocarbons and partially oxidized hydrocarbons, carbon monoxide, nitrogen oxides
(mostly nitric oxide), lead and other products from fuel additives, aerosols and sulfur dioxide. The hydrocarbons, nitrogen
oxides, and carbon monoxide are the principal contaminants. The other pollutants, with the possible exception of lead and
aerosols, normally are present in small quantities and not considered to be important atmospheric contaminants.

Crankcase

The emissions from this source mainly are cylinder blowby effluent comprising approximately 75% carbureted fuel-air
mixture and 25% exhaust gases diluted by air drawn into the crankcase for ventilating purposes. The pollutants This report,
published as Informative Report No. 4 of the Air Pollution Control Association's TA-10 Vehicular Exhaust Committee,
began to move through the fourteen-step approval procedure on July 12, 1963. Suggestions made by various members of
the Technical Council and the Board of Directors have been incorporated in this report, in accordance with the latest
procedures of the Technical Council, and approved by APCA's Board of Directors. It is now published as representing the
"best thinking of the Association." It is an extremely timely and informative report consist of the fuel with its associated
components and additives and of exhaust products. Because the volume of blow- by is small the quantity of exhaust gases
in crankcase gases is small. Hydrocarbon concentrations are high, however, as blowby is very similar to the carbureted
fuel-air mixture. Hydrocarbons are the only significant pollutants in crankcase emissions. Evaporative Losses Evaporative
losses occur from vents in the fuel storage and carburetor systems. These losses consist almost entirely of hydrocarbons
but also include small amounts of other compounds in the fuel, such as additives which are volatile at the temperatures
reached by the fuel.

Quantity of Pollutants

Exhaust

The volume of exhaust depends upon the air supplied to the engine and the quantity of fuel consumed. The fuel
consumption rate in turn depends upon the work performed by the engine. Exhaust volumes vary according to operating
modes with minimum flows of as little as three cfm at idle and deceleration in small vehicles to more than 200 cfm at full
load in large vehicles. Studies in Los Angeles have found that under driving conditions in that area the average exhaust
volume for American passenger cars is about 30 cfm (average fuel-air ratio of 1:13.5 and fuel consumption of 1.6 gal. per
hr). The average exhaust volume for small cars would be less than this figure and that from a large truck greater. Exhaust
concentrations also vary widely according to the vehicle, its driving modes and mechanical condition. Average