radiation chamber studies at equal hydrocarbon concentrations disclosed a 36 percent increase in the formation of formaldehydes with the alcohol-gasoline blend." A slightly higher rate of nitrogen dioxide formation was found with alcohol-gasoline mixtures and a slightly higher rate of ozone formation was found with gasoline mixtures.101

DIESELS

The increasing emphasis on the deleterious effects of the "invisible" emissions of gasoline engines probably tends to intensify public opinion against the noticeable diesel emissions. Largely because the overall fuel combustion is more complete in diesel engines and there are many fewer diesels in use compared to gasoline powered vehicles, diesel exhaust products are not considered of prime importance. However, diesel smoke and odors are undeniably a nuisance and are certainly capable of producing human discomfort.

Definitive regulations governing permissible levels of smoke and odor are largely nonexistent. Those that do exist require extensive enforcement agencies. California, however, on September 20, 1963, adopted a smoke standard for motor vehicles which permits:

(a) The shade, or the equivalent opacity of the shade, designated as No. 1 on the Ringelmann chart; or

(b) The shade, or equivalent opacity of the shade designated as Ringelmann No. 2, if the smoke is for a period not exceeding five seconds at a time.

After study, the State attorney general found the standard satisfactory for motor vehicle pollution control board purposes in certifying devices to control smoke but unacceptable for enforcement. At a later date the motor vehicle pollution control board decided not to stress diesel exhaust devices until acceptable methods of odor measurement are developed and an odor criterion is established.

On February 26, 1964, the Automobile Manufacturers Association recommended that its member companies adopt a smoke shade of No. 2 Ringelmann as a design standard effective July 1, 1964.102 On March 4, 1964, the Automobile Manufacturers Association announced the formation of a task group to study diesel smoke and make recommendations.

The ability to control diesel smoke has been demonstrated.103 104 Fuel quality, maintenance character and frequency, environmental conditions, and driver habits are important factors. Conservative power ratings of engines and a device to retard injector rack movement on "throttle" opening (applicable to vehicles equipped with hydraulic torque convertors) also assist in smoke control.

Catalytic afterburners for the control of diesel smoke and odor have undergone limited tests.105 Results indicate a worthwhile reduction in these emissions, but before such devices can be considered on a broad scale, more comprehensive studies are required.

Fuel additives for the reduction of smoke currently are said to display promise.106 Their effectiveness has not been fully established nor have factors such as cost, side effects on engine performance, and toxicity been evaluated.

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