Taking deep breaths can help relieve stress, but depending on where you live, the air you breathe may lead to other health problems.

A new study by a team of MIT researchers has found that air pollution in the U.S. contributes to more than 200,000 premature deaths each year. The researchers tracked ground-level emissions from six different sectors, including industrial, residential and vehicular emissions. Their findings, published in Atmospheric Environment, show emissions from ground transportation to have the greatest impact on health, causing 53,000 early deaths each year.

The team also did a state-by-state analysis and found California to be the most adversely affected state, suffering an estimated 21,000 air pollution-related early deaths per year.

These findings underscore the importance of clean air, which also relates to the importance of urban forests. With a single tree able to absorb up to 10 pounds of air pollutants each year, urban forests are a key strategy in helping to reduce and mitigate air pollution.

In May, American Forests launched our Community ReLeaf program in five cities across the U.S., each of which is the site of an assessment and restoration project focused on that city’s particular needs. Given the findings above, it may come as no surprise that the Pasadena, Calif., Community ReLeaf project is largely focused on air quality. The assessment phase of the Pasadena project is measuring the benefits of the city’s public street trees in both economic and health terms, including the capacity of the urban forest to help address air pollution and smog, two of the city’s major challenges. The assessment will be used to inform Pasadena’s future Urban Forest Management Plan. Stay tuned for the results of our research and assessment this fall.