Trees clean our air: In addition to absorbing CO2 and producing oxygen, they also play an important role in filtering some of the most common pollutants. During a heat wave, however, a method that plants employ to conserve water also prevents them from filtering as much pollution. When the ground is dry, plants close their stomata — pore-like openings — to keep water in, but the stomata are also the mechanism through which they absorb all that air pollution, including ozone. While atmospheric ozone protects us from harmful cosmic rays, close to the earth, it’s the primary component of smog. So while water stays in when plants close their stomata, ozone and other pollutants stay out — out in the air we’re breathing.
As important as urban forests’ role in cleaning our air is, reading about this study brought to mind another important benefit of urban forests. They don’t just clean the air; they also cool it. This benefit of trees is especially significant in urban areas where what’s known as the heat island effect is in place. Because our buildings, streets and paved surfaces store the sun’s heat, temperatures in the city are higher than those in surrounding areas. Planting and caring for a healthy urban forest is one way to help cool cities.
That’s why we work to restore forests globally and why we’re starting our new project, Community ReLeaf, to help cities gain insight into their urban forests — insights that can inform management and planting strategies. Heat waves will continue to be a fact of life, but by doing what we can to mitigate the heat island effect, we may also be helping our forests clean the air.