Ci-trees

City living has a lot going for it. There is the culture, the multiplicity of activities, the range of employment opportunities, the diversity and the general buzz that goes with all of it. There are of course, also some downsides and perhaps chief among these is the pollution. As often happens in cities though, there are super-heroes at hand to protect you from the worst ravages of pollution and these super-heroes are clad in brown and green. They are, of course, trees.

Pollution is a sweeping term but in fact air pollution comes in varying shapes and sizes. Particle pollution (also called particulate matter or PM) is the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope. The size of particles is directly linked to their potential for causing health problems. “Inhalable coarse particles”, such as those found near roadways and dusty industries, are larger than 2.5 micrometres and smaller than 10 micrometres in diameter. “Fine particles” (PM2.5) such as those found in smoke and haze, are 2.5 micrometres in diameter and smaller. Fine particulate air pollution has serious health effects, including premature death, lung inflammation, atherosclerosis and altered heart function.

In this new study researchers used the U.S. Environmental Protection Agency’s BenMAP program to estimate the incidence of adverse health effects across cities including Atlanta, Baltimore, Boston, Chicago, Los Angeles, Minneapolis, New York City, Philadelphia, San Francisco and Syracuse, New York. This data was then correlated with PM2.5 concentrations and the incidence of trees.

It was found that the removal of PM2.5 by urban trees is substantially lower than for larger particulate matter (particulate matter less than 10 microns – PM10), but the health implications and values are much higher. The total amount of PM2.5 removed annually by trees varied from 4.7 metric tons in Syracuse to 64.5 metric tons in Atlanta. The value of this in terms of reduced health costs varied from US$1.1 million in Syracuse to US$60.1 million in New York City. On average trees were estimated as saving one life per year in every city and in a city like New York as saving equivalent to eight lives annually.

Studies like this serve to highlight that is not an act of generosity to preserve and grow and trees and plants; it is an act of intelligent responsibility.