Ambient ozone, a secondary pollutant formed by reactions between nitrogen oxides and volatile organic compounds in the presence of sunlight, has consistently been linked to adverse health effects. Future ozone levels are particularly sensitive to climate change as its formation depends strongly on weather conditions. Chang et al. (2010) examined the risk of future ozone levels on non-accidental mortality via statistical modeling. The authors used data from climate model outputs, historical meteorology, and ozone observations, and a health surveillance database to model present-day relationships between observed ozone concentrations and meteorology, future ozone concentrations, daily community-level mortality counts, and relative risks associated with short-term exposure to ambient ozone. The study estimated that there will be an increase of 0.43 ppb in average ozone concentration during the 2040s compared to 2000, corresponding with a 0.01% increase in mortality rate and 45.2 premature deaths in the study communities. — Carolyn Campbell
Chang, H.H., Zhou, J., Fuentes, M., 2010. Impact of climate change on ambient ozone level and mortality in southeastern United States. International Journal of Environmental research and Public Health 7, 2866–2880.
Ground-level ozone is mainly found in urban settings due to emissions from industrial facilities, power generation, and vehicle exhaust. It is linked to adverse health effects including morbidity and mortality for cardiovascular and respiratory diseases. There is concern that climate change will lead to increased levels of ozone, as weather factors such as temperature, wind speed, cloud cover, solar radiation, and atmospheric mixing affect ozone’s formation. In the Eastern United States, episodes of high ozone are usually associated with slow moving high-pressure systems characterized by warm temperature, light wind, and cloudless skies.
The study by Chang et al. seeks to quantify the impact of future ozone levels on non-accidental mortality in 19 communities throughout Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee. First, the authors modeled present-day relationships between observed ambient maximum daily 8-hour average ozone concentrations and three meteorology variables during 2000. Next the authors estimated the association between acute exposure to ambient ozone and mortality. Future ozone concentrations were predicted using future daily forecasts of temperature, solar radiation, and cloud-cover. Finally, the authors calculated the number of attributable deaths using the total number of deaths in 2000, the difference in average ozone between 2000 and 2040, ad the overall relative risk of mortality per ppb increase in ozone concentration.
It was found that ozone concentration is positively associated with temperature and solar radiation, but negatively associated with total cloud cover. Additionally, the association between weather variables and ozone levels can vary across states. The estimated adverse association between daily mortality per 10 ppb unit increase in maximum 8-hour ozone level on day with lag 0, 1, and 2 was 0.11, 0.23, and 0.11 respectively, with an overall relative risk of 0.26. Average 2041–2050 ozone levels were predicted to increase by 0.43 ppb compared to 2000, corresponding to a 0.01% increase in mortality rate associated with future ozone levels due to climate change alone.
The study suggests that ambient ozone levels and corresponding deaths will increase in the future due to climate change. However, the health impact analysis does not account for future regulatory policies that control local and regional emissions of ozone precursors including expected changes in population structure, behaviors, and size and the effects of other pollutants and meteorology on ozone levels. While climate change will likely have an effect on ozone levels, other factors may also influence the number of attributable deaths.