Nitrogen Oxides

In a follow-up study to previous research, Dr. Mercer and colleagues at Duke University exposed three groups of rats continuously for six weeks to 2 or 6 ppm nitric oxide (NO) or to filtered air to learn more about the toxicity of NO so as to compare it with two other important oxidants, ozone and nitrogen dioxide (NO₂). At the end of the exposure period he used an electron microscope to measure the number of holes in the alveolar septa and to observe other structural changes, such as in the surface area and the number and type of other abnormalities in the alveolar septa.

In two separate studies, Drs. Koenig and Utell examined the effects of exposing healthy subjects and subjects with asthma to combined oxidant and acid pollutants. Each team of investigators conducted studies in which human volunteers received either combined or sequential exposures to oxidant gases and acid aerosols and standard pulmonary function tests were performed and symptoms were recorded. Dr. Koenig and colleagues exposed 28 adolescents with asthma to varying concentrations of ozone, nitrogen dioxide, and sulfuric acid. Dr. Utell and colleagues examined the effects of sequential exposures to sulfuric acid and ozone on pulmonary function in 30 subjects with asthma and 30 healthy subjects between the ages of 18 and 45. 

Ozone and nitrogen dioxide are highly reactive oxidant gases that are derived from the combustion of fossil fuels and the atmospheric transformation of these combustion products. A major unanswered question is whether or not exposure to oxidant air pollutants contributes to lung cancer. Dr. Witschi and colleagues at the University of California at Davis examined whether exposure to ozone or nitrogen dioxide enhances the development of tumors induced by the chemical carcinogen diethylnitrosamine (DEN), particularly neuroendocrine tumors, in the respiratory tract of hamsters.