Scientists have long known that air pollution is a serious health hazard that increases the risk of premature death. But a new study may come as a shock. Researchers have found that people who live in urban areas are at an increased risk of dying after being exposed to high ozone levels just one week before.
Ozone is a corrosive gas produced as a byproduct of burning fossil fuels.
Researchers studied data collected over a 14-year period in 95 U.S. cities, and they found there was a small, but significant, increase overall in the number of deaths one-week after ozone levels rose. It did not matter whether ozone levels crept up one day or all seven days during the previous week.
Study author Michelle Bell of Yale's School of Environment in New Haven, Connecticut says the data do not translate easily into numbers.
"It is hard to look at in terms of absolute numbers, in terms of how many people are dying from ozone," Michelle Bell said. " But really we can say that the higher ozone levels correspond to higher mortality and lower ozone levels correspond to lower levels of mortality."
The scope of the study conducted by Professor Bell and colleagues at Johns Hopkins University is sweeping, representing 40 percent of the U.S. population.
"This is one of the largest studies of ozone and mortality that has ever been conducted," explained Professor Bell. "There have been many different studies of ozone and human health. And there also have been some studies on ozone and mortality before our study. But most of those were been looking at a single city or a small number of cities, or combining several independently conducted results, whereas our study starts with a very large data set to look at ozone mortality on a national basis."
The United States Environmental Protection Agency is currently revising air pollution standards. Yale's Michelle Bell estimates that reducing total pollution, including exposure to ozone, by one-third would result in 4,000 fewer deaths per year.