Air quality standards for selected pollutants were mandated by the U.S. Clean Air Amendments of 1970, which aimed primarily at the protection of human health against atmospheric contaminants. The act states that among its purposes is “to protect and enhance the quality of the nation’s air resources so as to promote the public health and welfare and the productive capacity of its population.” The stimulus for establishing a sulfur dioxide standard was a significant body of evidence indicating that ambient sulfur dioxide was associated with adverse health effects at the high concentrations measured during recognized air pollution diasters and with less severe increase in morbidity and mortality at lower concentrations.
Much additional information has been obtained since the original air quality criteria document for sulfur oxides was published in early 1969 (USDHEW 1970). In general, epidemiologic studies have tended to confirm the association of adverse human health effects with ambient sulfur dioxide concentrations around the primary standard of 0.03 ppm (80 ug/m3)† annual arithmetic mean. The maximum 24 hour standard, not to be exceeded more than once yearly, is −.14ppm (365 ug/m3). It is generally recognized, and should be emphasized that this epidemiologic association does not necessarily imply causality. In fact, exposure of humans to sulfur dioxide in chambers has shown clearly
that sulfur dioxide by itself is incapable of producing an acute response in man even at concentrations considerably higher than 0.03 ppm.
This apparent discrepancy between epidemiologic observation and the results of controlled experiments is explainable by the presence in polluted air of sulfur dioxide oxidation products (such as sulfuric acid and particulate sulfates), which are potentially more toxic, and possibly by the synergistic effects of sulfur dioxide and other pollutants, including particles and ozone, within the respiratory system. It would therefore be inappropriate to use the failure to observe a human response to sulfur dioxide during controlled exposure as a reason to allow an increase in the emission of sulfur dioxide.
The literature concerning the health effects of sulfur oxides has recently been reviewed by scientific panels in the United States and elsewhere (NAS 1974, Rall 1974, Holland 1972, y NATO 1972). Those reviews have generally been organized by scientific subdiscipline, which provides a useful framework for consideration of specific points and integration of available information. They have been prepared by competent and thorough panels and are in the public record. The present document is organized by human disease processes that are believed to be related to the effects of sulfur oxides, and both animal experiments and controlled human exposures will be discussed according to disease process. It is hoped that this format will prove more intelligible to nonscientists, particularly those involved in decisions concerning clean air strategy.
Holland W.W. (1972) Air Pollution and Respiratory Disease. Westport, Connecticut: Technomic Publishing Co.
National Academy of Sciences (1974) Panel on Airborne Particles. Airborne particles and sulfur oxides, pp. 391–412. In National Academy of Sciences, Coordinating Committee on Air Quality Studies. Vol. 2. Health Effects of Air Pollutants. Prepared for the U.S. Senate Committee on Public Works. Washington, D.C.: U.S. Government Printing Office.
North Atlantic Treaty Organization (1972) Committee on the Challenges of Modern Society. Air Pollution. Air Quality Criteria for Sulfur Oxides. Washington, D.C.: U.S. Government Printing Office, 324 pp.
Rall, D.P. (1974) Review of the Health effects of sulfur oxides. Environ. Health Perspect. 8:97–121.
U.S. Department of Health, Education, and Welfare (1970) Public Health Service. Air Quality Criteria for Sulfur Oxides. National Air Pollution Control Administration Publication No. AP-50. Washington, D.C.: U.S. Government Printing Office, 178pp.