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<br />Or' ." 'l.' <br />U _l.. i. ._,'~ <br /> <br />"n.. <br />.uotochemical oxidants have emerged relatively recently as a <br /> <br />major health problem, and research relating to their effects <br /> <br />on human health is still in its infancy. However, studies <br /> <br />have shown that eye irritation begins when peak oxidant levels <br /> <br />reach 0.10 parts per million. Increased frequency of asthma <br /> <br />attacks occurs in SOme patients on those days when hourly con- <br /> <br />centrations average 0.05 to 0.06 parts per million. Even the <br /> <br />healthiest persons may be affected; however, a study of cross- <br /> <br />country runners in a Los Angeles high school showed that their <br /> <br />performances suffered when hourly average oxidant levels ranged <br /> <br />from 0.03 to 0.30 parts per million. <br /> <br />"Less is known about the effects on health of nitrogen oxides, <br /> <br />which play such an important part in producing photochemical <br /> <br />pollution. They have been little studied until recently. How- <br /> <br />ever, evidence so far suggests that they may be harmful to <br /> <br />human health. A study in Chattanooga, Tennessee, linked very <br /> <br />low levels of these oxides in the air to children's suscepti- <br /> <br />bility to Asian flue. <br /> <br />'~he lowest particulate levels at which health effects have <br /> <br />been noted in the United States were reported at Buffalo. The <br /> <br />Buffalo study suggests that the overall death rate rises in <br /> <br />areas with an annual average concentration ranging from 80 to <br /> <br />100 micrograms per cubic meter. The study also reveals a.tie <br /> <br />between these levels of particulate matter and gastric cancer <br /> <br />in men 50 to 69 years old. A similar association was found <br /> <br />31 <br />