The Health of a City Depends on Its Trees

In addition to all the obvious benefits of having trees in and around our urban landscape — aesthetic quality, shade, a general boon to our mental health — did you know trees play a major role in keeping our air clean? Trees disperse and remove pollutants such as carbon dioxide (through photosynthesis), nitrogen dioxide, and they shield us from ozone. Gases are absorbed through pores (stomata), they block particulate matter from reaching the atmosphere, thus making our concrete and blacktop environments much healthier places to dwell. 

In 1994, a study showed, trees in New York City removed approximately 1,821 metric tons of air pollution at an estimated value to society of $9.5 million. Air pollution removal by urban forests in New York was greater than in Atlanta (1,196 t; $6.5 million) and Baltimore (499 t; $2.7 million), but pollution removal per m2 of canopy cover was fairly similar among these cities (New York: 13.7 g/m2 /yr; Baltimore: 12.2 g/m2 /yr; Atlanta: 10.6 g/m2 /yr)h. These standardized pollution removal rates differ among cities according to the amount of air pollution, length of in-leaf season, precipitation, and other meteorological variables. Large healthy trees greater than 77 cm in diameter remove approximately 70 times more air pollution annually (1.4 kg/yr) than small healthy trees less than 8 cm in diameter (0.02 kg/yr)k. Air quality improves with increased percent tree cover and decreased mixing-layer heights. In urban areas with 100% tree cover (i.e., contiguous forest stands), short-term improvements in air quality (one hour) from pollution removal by trees were as high as 15% for ozone, 14% for sulfur dioxide, 13% for particulate matter, 8% for nitrogen dioxide, and 0.05% for carbon monoxide.” (Nowak, 2002, pg. 1)

Greenhouse gases circulate at a global level. So the existence of trees is important all over the world. Forests absorb and store as much as 30% of the carbon emissions from human activities. However, burning them will release it back into the atmosphere.

Though the importance of trees is worldwide, we might be most concerned with the trees in our local parks and schools. The quality of the air we breathe is directly connected to the trees closest to us.

This relationship between the global and local benefits of trees beyond just their beauty is what makes them indispensable for the protection of our planet and our health.

Want to learn more about how trees clean the air we breathe? Click here.

Or click here to learn about exactly how trees breathe.