Ozone is formed through a chemical reaction that occurs when sunlight interacts with nitrogen oxides and other organic compounds that are generated by coal-burning, vehicle exhaust and some natural sources.

The team studied 89 healthy adults living in Changsha City, China, for one year. They monitored indoor and outdoor ozone levels, along with other pollutants. Of the 89 participants, 25 (28%) were women and the mean (SD) age was 31.5 (7.6) years. The 24-hour ozone exposure concentrations ranged from 1.4 to 19.4 parts per billion (ppb), corresponding to outdoor concentrations ranging from 4.3 to 47.9 ppb.

At four intervals, the study team took participant blood and urine samples and used a breathing test called spirometry to examine a set of factors that could contribute to cardiovascular and respiratory disease.

The team examined inflammation and oxidative stress, arterial stiffness, blood pressure, clotting factors and lung function in participants. They noted blood platelet activation (a risk factor for clotting) and an increase in blood pressure, suggesting a possible mechanism by which ozone may affect cardiovascular health. These effects were found with ozone exposure lower than that which affects respiratory health, and lower than current Environmental Protection Agency (EPA) air quality standards.

This study shows that standards for safe ozone exposure should take into account its effect on cardiovascular disease risk. In 2015, 108 million Americans—one third of the population—lived in counties with ozone levels that exceeded standards set by the EPA. In contrast, only 31 million Americans live in counties where other pollutants exceed EPA standards.

—Junfeng (Jim) Zhang, from Duke and Duke Kunshan University

The production of ozone globally will be exacerbated by a warmer climate, so it will be an increasing trend with climate change, said Zhang. Ozone is a difficult pollutant to control because its creation in the atmosphere is complex. For example, a reduction in nitrogen oxides does not necessarily mean a reduction in ozone levels, Zhang explained.

This study was supported by grants from the National Natural Science Foundation of China (51420105010), the National Institute of Environmental Health Sciences (T32-ES021432) and the Duke Global Health Institute Doctoral Scholars Program.

Resources

• Drew B. Day, Jianbang Xiang, Jinhan Mo, Feng Li, Mingkei Chung, Jicheng Gong, Charles Weschler, Pamela A Ohman-Strickland, Jan Sundell, Wenguo Weng, Yinping Zhang, Junfeng (Jim) Zhang (2017) “Pathophysiologic Mechanisms Underlying Cardiorespiratory Effects of Ozone in healthy Adults” JAMA Internal Medicine, doi: 10.1001/jamainternmed.2017.2842