Trees and Air Pollution – It’s a complicated relationship, but a healthy one

Tuesday, July 16, 2019
Ah July – the heart of summer and a great month to get outside and explore your urban and community forests and other natural areas.   But the air quality in our urban areas, especially at this time of year, can be unhealthy.   The good news is that while the relationship between trees and air pollution is complicated, overall trees have been shown to have a positive effect on reducing air pollution, making your outdoor activities healthier and more enjoyable.
So how does air pollution impact your health and how are trees involved?

Air pollution, such as particulates (small particles usually generated by the burning of fuels to create energy) and ground level ozone (a gas which requires certain chemical compounds + heat + sunlight to form), can affect human health in many ways.  It can produce just a general feeling of discomfort, to increased respiratory difficulties like asthma, coughing, airway irritation, irregular heartbeat, and even premature death in people with heart or lung disease.  Fortunately, healthy trees play an important role in reducing air pollution.  For example, a tree’s leaves can "capture" airborne particulate pollution, especially the very small particles which are the most dangerous, removing them from the air we breathe.  Trees reduce the formation of ground level ozone by both absorbing contributing chemical compounds (such as volatile organics) through their pores and by lowering the ambient temperature.  Trees create cooling by converting water from the soil to water vapor in the atmosphere, which carries heat away from its point of origin. Since ground level ozone requires heat to form, cooler temperatures equal less ozone.  This cooling effect has the added benefit of reducing energy use.  Trees shade buildings during the summer and block winds in winter; less energy use means less air pollution generated by the production of energy for cooling and heating our buildings and vehicles.

OK, now for the complications.  Dense tree canopy can restrict airflow or trap pockets of polluted air at ground level preventing the dilution of air pollution by currents of cleaner air.  And while trees play a role in reducing volatile organic compounds (VOCs) created by energy production, they themselves are VOC emitters.  In areas with a large percentage of high VOC emitting trees, ozone levels can be eight times higher than in areas with low-VOC emitting trees. Lastly, we’d be remiss if we didn’t note that trees also emit pollen, a type of particulate.  Fortunately, most pollen grains are larger than the size of particles that have the greatest impacts on human health.

So, armed with the above information, what can you do?  Take these tree related actions to improve your overall health and well-being, and reduce air pollution:
  • Plant trees and support programs that help to maintain and increase a healthy tree canopy in your town;
  • Maximize the use of low VOC emitting trees in areas with air pollution problems;
  • Strategically plant trees to reduce energy use;
  • Use long-lived and low maintenance trees to reduce pollution emissions from planting, maintenance, and tree removal;
  • Diversify your urban and community forest so that no one tree dominates; and
  • Ensure trees have enough water to enhance their cooling capabilities.
After all, a healthy relationship is worth the effort!

This bermed shelterbelt was conceived and planted as part of the Heart of Camden's Environmental Mitigation Master Plan for the Waterfront South neighborhood of Camden, NJ to overcome decades of environmental injustice.  The shelterbelt serves as a visual screen and windbreak between local industry, the County sewage treatment plant, and the historic residential neighborhood.