Relax and take a deep breath. On second thought, you may not want to. The average American breathes in 3,400 gallons of air each day, but according to the American Lung Association's Web site, those gulps of oxygen can sometimes cause serious health problems, thanks to smog-filled cities and smoke-filled bars. The site provides alarming statistics, including the fact that the number of asthma-related deaths has more than doubled since 1980. In addition, each year close to 361,000 Americans die of lung disease, the country's No. 3 killer. The Data and Statistics link offers reports in PDF format on such topics as air quality, pollution and also disease and morbidity rates. For those interested in self-inflicted lung abuse, the site contains a detailed annual report on trends in tobacco use.