It has taken a quarter of a century, but US researchers say their work has finally enabled them to determine to what extent city air pollution impacts on average life expectancy.
The project tracked the change of air quality in 51 American cities since the 1980s. During that time general life expectancy increased by more than two and half years, much due to improved lifestyles, diet and healthcare. But the researchers calculated more than 15% of that extra time was due to cleaner air.
"We think about five months of that is due to the improvement of air quality," said Dr Douglas Dockery, head of the Environmental Health Department at Harvard School of Public Health in Boston, which undertook the research. He added that, due to the relatively clean air in the US, the impact was far larger than anticipated.
Dr Dockery said there were many factors which had an impact on life expectancy. But he added: "Clean or dirty air is something that is being imposed on you. You do have a choice on whether you smoke, drink, exercise or what type of food you eat. But you do not have a choice on what air you breathe."
Dr Dockery believes that if his research was transposed onto the heavily polluted cities of the developing world, such as Beijing or Mexico City, the life expectancy impact would be far greater.