Air pollution kills roughly 2.5 million per year, says study

Scott Sutherland

According to new research from an international team of scientists, a combination of air pollution and climate change is killing an estimated 2.5 million people every year, and these numbers are expected to climb as industrial emissions increase.

The study gathered air pollution data from all over the world, specifically for ground-level ozone and fine particulate matter — the two components of urban smog that have the strongest impact on peoples' health — and used computer modeling to compare changes in the levels of these pollutants to changes in the number of deaths due to respiratory disease, heart disease and lung cancer. All of these diseases have been shown, over the years, to have a very strong connection to air pollution levels. It found that fine particulate matter (PM2.5) was responsible for an estimated 2.1 million deaths per year, with ground-level ozone adding another 470,000 casualties every year.

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"Our estimates make outdoor air pollution among the most important environmental risk factors for health," said study co-author Jason West, according to the Institute of Physics. Many of these deaths are estimated to occur in East Asia and South Asia, where population is high and air pollution is severe."

Indeed, according to their results, Asia accounted for the greatest number of annual deaths (over 85%), with East Asia and India combined taking the majority of the burden of that, with over half the total number between the two. Europe added a little over 7% to the total, Africa contributed over 3.5%, North America about 3%, and South America and Australia accounted for the rest.

One added factor that this study looked into, where most others hadn't, was the contribution of climate change.

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

According to their results, the effects of climate change on the air pollution levels contributed 1500 deaths due to ozone and 2200 deaths from PM2.5, each year. This is a very small amount compared to the total, and the researchers point out that "it cannot be clearly concluded that past climate change has increased air pollution mortality."

However, temperature, humidity and precipitation all have an effect on the formation of ozone and particulate matter. High temperature and humidity work together to make higher concentrations of these pollutants, whereas greater amounts of cloud cover and precipitation tend to mean lower concentrations. All three of these factors are expected to increase as climate change continues, so the overall effect is very complicated to figure out. The way the researchers helped work around this problem was to use ensemble computer models.

Ensembles are created when several computer models are run at the same time, with the same data, and then the results of all the models are combined together. The more models that get a particular result for a particular area, the more that result shows up in the final ensemble. If only one model gets a particular result, that will receive far less attention in the final ensemble. This method produces a stronger end result because weaknesses of different models are compensated for by strength of others, and the result is more accurate, overall.

"This would caution against using a single model in the future, as some studies have done," said West in the IOP article.

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In a 2008 report by the Canadian Medical Association, the number of air pollution-related deaths was an estimated 21,000 people, most due to the cumulative effects of long-term exposure, but over 2,600 of them were expected due to short-term exposure. That same report projects that these numbers will increase to 710,000 from long-term exposure and 90,000 from short-term exposure, by the year 2031.

In addition, the estimated 92,000 emergency room admissions and 620,000 doctor's office visits in 2008, due to air pollution-related illnesses, is expected to increase to 152,000 and 940,000 in 2031, respectively. The cost of these visits was estimated at $8 billion in 2008, and will likely increase to $250 billion by 2031, if air quality doesn't improve.

Environment Canada's Air Quality Health Index (AQHI) was specifically designed to not only inform the public about air quality concentrations, but also relate those concentrations to the effects they have on the population. They also have guidelines on how to tell if you're one of those with increased risk due to exposure, and they provide current conditions to allow the public to see the risk of exposure.

(Photo courtesy: Reuters)

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