Standard: API 4006


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Polynuclear aromatic (PNA) compounds have been known to chemists for many years and have been studied extensively because of their role in causing cancer. As extensive research studies have been undertaken to identify all types of atmospheric pollutants and to assess their importance from a health standpoint, attention has been focused on polynuclear aromatic compounds, together with many other atmospheric constituents.

Polynuclear aromatic compounds have been isolated from motor vehicle exhaust, but the factors that control their emission by motor vehicles are not well defined. Therefore, the American Petroleum Institute has requested a study to collect information available in the literature, to evaluate this information to the extent possible, and to identify gaps in our present knowledge. This study also includes recommendations for further experimental work which might be appropriate to permit a more complete evaluation of the problem.

It is not the purpose of this study to delve into the medical problems of the degree of hazard to health and the relationships between atmospheric PNA compounds and human cancer. However, it is important to review some of the pertinent factors concerning this subject in order to understand the concern which exists. Of greater importance to the petroleum industry is the possibility of regulations requiring changes in fuels or vehicle operating conditions, as these might affect the emission of polynuclear aromatic compounds by motor vehicles.

Another reason for considering additional studies at this time is the many air pollution control measures being adopted or considered which a r e designed to reduce pollution from motor vehicles, some of which may unintentionally influence the emission of PNA compounds. Because of the necessity to control vehicle emissions which contribute to photochemical air pollution, exhaust control devices have been required recently in California and will be required nationally, starting in the fall of 1967. The extent to which these devices influence the emission of PNA compounds is not known and should be investigated. Regulatory action requiring changes in fuel composition, such as a reduction in the amount of lead-containing additives or limitations on the use of other metallic additives, may also influence the formation of PNA compounds. Also, control of nitric oxide emissions from motor vehicles has been discussed as a future possibility.

In addition to these possible control measures, some public health officials are considering limitations on emissions of carcinogenic materials. The State of California has adopted an ambient air quality standard which pertains to carcinogenic compounds, although numerical limits have not been specified due to a lack of information. The ambient air standards do specify numerical limits for many contaminants, but, for carcinogens, the standard states as follows: "Carcinogens include a few organic compounds such as some polycyclic hydrocarbons and Some metals such as arsenic and chromium. Studies on effects of such substances are currently under way, but there are not sufficient data at present to set standards. In the meantime, it is recommended that concentrations of carcinogens in air should be kept as low as possible. "(1)*

This statement in an ambient air standard, even though numerical limits have not been specified, indicates the degree of concern among public health officials. It can be anticipated that numerical standards will be adopted when sufficient information is available to permit such action. Therefore, a thorough understanding of the factors involved in the formation and emission of PNA compounds from all sources is important for a guide in the setting of such standards, and to assist the petroleum and automotive industries in meeting such objectives as may relate to motor vehicles if and when the standards are adopted.

This study is based in part on a previous summary prepared for the Coordinating Research Council (2) which attempted to summarize briefly the major factors concerning the occurrence of high molecular weight compounds in vehicle exhaust. The organization and a portion of the information used in this report are taken from that summary.

However, a detailed literature survey has been conducted to provide a more complete evaluation and a more extensive List of References than were needed for the previous summary. In all, over 200 literature references were checked in evaluating information of interest to this study. Some of these were eliminated due to obvious duplication or because the results were preliminary in nature. The List of References of this report lists those which remained after evaluation and provides the basis for the conclusions and recommendations for future work which are also presented.

*Numbers in parentheses refer to List of References at end of text.

Organization: American Petroleum Institute
Document Number: api 4006
Publish Date: 1967-08-28
Page Count: 41
Available Languages: EN
DOD Adopted: NO
ANSI Approved: NO
Most Recent Revision: YES
Current Version: NO
Status: Inactive