As part of our air purifier buying guide, we will evaluate some of the evidence regarding the health benefits of using an air purifier. A recent Harvard and Bingham Young University Study showed that life expectancy improved by cleaner air being used in a person's bedroom. Even in cities with relatively low levels of pollution, less indoor air pollution improves life expectancy measurably. The study evaluated changes in air pollution in 51 American cities between 1980 and 2000 and the life expectancy of the inhabitants in those cities during the same time period. Co-author of the study, Arden Pope III, remarked that "…such a significant increase in life expectancy attributable to reducing air pollution is remarkable." Life expectancy increased by 10 months, in cities that had the largest improvements on air pollution. "We find that we're getting a substantial return on our investment in improving our air quality," writes Arden Pope III. The prevalence of cardiopulmonary and cardiovascular diseases decreased considerably due to improved air quality. Prof. Douglas Dockery is the Director of the Harvard NIEHS Center for Environmental Health and is a co-author of the study. His research over the last couple of years shows the causal link between even relatively low concentrations of combustion-related particles and increases in morbidity and mortality. "The efforts to reduce particulate air pollution concentrations leads to substantial and measurable improvements in life expectancy," says Prof. Dockery. Air pollution not only decreases life expectancy in adults but also causes chronic respiratory diseases in children.