July 12, 2013

More than two million deaths occur each year as a direct result of human-caused outdoor air pollution, a new study has found. Although others have suggested that a changing climate may exacerbate effects of air pollution and increase death rates, the study also shows that previous climate change has a minimal effect and accounts only for a small proportion of current deaths related to air pollution.

Dr. Jason West

Dr. Jason West

Co-authored by Jason West, PhD, assistant professor, and Raquel A. Silva and Yuqiang Zhang, doctoral students, all in the Gillings School of Global Public Health’s Department of Environmental Sciences and Engineering, the research was published online July 12 in the journal Environmental Research Letters.

West, Silva, Zhang and a team of international scientists estimate that about 470,000 people die each year because of human-caused increases in ozone.They also estimate that about 2.1 million deaths result each year from human-caused increases in fine particulate matter – tiny particles suspended in the air that can penetrate deep into the lungs, causing cancer and other respiratory diseases.”Our estimates make outdoor air pollution among the most important environmental risk factors for health,” West said. “Many of these deaths are estimated to occur in East Asia and South Asia, where a large population is exposed to severe air pollution.”

However, the study finds that the number of these deaths that can be attributed to changes in the climate since the industrial era began is relatively small. It estimates that climate change is responsible for only 1,500 deaths due to ozone and 2,200 deaths related to fine particulate matter each year. Different models disagreed on whether climate change has increased or decreased the number of deaths due to air pollution.

Climate change affects air pollution in many ways, possibly leading to local increases or decreases in air pollution. For instance, temperature and humidity can change reaction rates, which determine the formation and lifetime of a pollutant, and rainfall can determine how long pollutants accumulate.

Higher temperatures also can increase emissions of organic compounds from trees, which then can react in the atmosphere to form ozone and particulate matter.

“Very few studies have attempted to estimate the effects of past climate change on air quality and health,” West said. “We found that the effects of past climate change are likely to be a very small component of the overall effect of air pollution.”

The researchers used an ensemble of global atmospheric chemistry-climate models to simulate concentrations of ozone and fine particulate matter in the years 1850 and 2000. A total of 14 models simulated levels of ozone, and six models simulated levels of fine particulate matter.

Previous epidemiological studies were used to assess how specific concentrations of air pollution from the climate models related to current global mortality rates.

The findings were comparable to previous studies that have analyzed air pollution and mortality; however, there was some variation in results depending on which climate model was used.

“We also have found significant uncertainty based on the results we get when using different atmospheric models,” West said. “This would caution against using a single model in the future, as some studies have done.”

Gillings School of Global Public Health contact: David Pesci, director of communications, (919) 962-2600 or dpesci@unc.edu.

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