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 As we all know by now, heat from Earth is trapped in the atmosphere due to high levels of carbon dioxide (CO2) and other heat-trapping gases that prohibit it from releasing heat into space, creating a phenomenon known as the "greenhouse effect." Trees remove (sequester) CO2 from the atmosphere during photosynthesis to form carbohydrates that are used in plant structure/function and return oxygen back to the atmosphere as a byproduct. About half of the greenhouse effect is caused by CO2. Trees therefore act as a carbon sink by removing the carbon and storing it as cellulose in their trunk, branches, leaves and roots while releasing oxygen back into the air.
But consider how trees also reduce the greenhouse effect by shading our homes and office buildings. This reduces air conditioning needs up to 30 percent, thereby reducing the amount of fossil fuels burned to produce electricity. This combination of CO2 removal from the atmosphere, and the cooling effect makes trees a double-threat to global warming. Not convinced? Here are few facts to chew on:
* One tree that shades your home in the city will also save fossil fuel, cutting CO2 buildup as much as 15 forest trees.
* Approximately 800 million tons of carbon are stored in U.S. urban forests with a $22 billion equivalent in control costs.
* Planting trees remains one of the cheapest, most effective means of drawing excess CO2 from the atmosphere.
* A single mature tree can absorb carbon dioxide at a rate of 48 lbs./year and release enough oxygen back into the atmosphere to support two humans.
* Each person in the United States generates approximately 2.3 tons of CO2 each year. A healthy tree stores about 13 pounds of carbon annually, or 2.6 tons per acre each year. An acre of trees absorbs enough CO2 over one year to equal the amount produced by driving a car 26,000 miles. An estimate of carbon emitted per vehicle mile is between 0.88 lb. CO2/mi. �" 1.06 lb. CO2/mi. (Nowak, 1993). Thus, a car driven 26,000 miles will emit between 22,880 lbs CO2 and 27,647 lbs. CO2. Thus, one acre of tree cover in Brooklyn can compensate for automobile fuel use equivalent to driving a car between 7,200 and 8,700 miles.
* If every American family planted just one tree, the amount of CO2 in the atmosphere would be reduced by one billion lbs annually. This is almost 5 percent of the amount that human activity pumps into the atmosphere each year.
* The U.S. Forest Service estimates that all the forests in the United States combined sequestered a net of approximately 309 million tons of carbon per year from 1952 to 1992, offsetting approximately 25 percent of U.S. human-caused emissions of carbon during that period.
* Over a 50-year lifetime, a tree generates $31,250 worth of oxygen, provides $62,000 worth of air pollution control, recycles $37,500 worth of water, and controls $31,250 worth of soil erosion.
Trees also remove other gaseous pollutants by absorbing them with normal air components through the stomates in the leaf surface. Some of the other major air pollutants and their primary sources are:
* Sulfur Dioxide (SO2) - Coal burning for electricity/home heating is responsible for about 60 percent of the sulfur dioxide in the air. Refining and combustion of petroleum products produce 21 percent of the SO2.
* Ozone (O3) - is a naturally occurring oxidant, existing in the upper atmosphere. O3 may be brought to earth by turbulence during severe storms, and small amounts are formed by lighting. Most O3 - and another oxidant, peroxyacetylnitrate (PAN) - come from the emissions of automobiles and industries, which mix in the air and undergo photochemical reactions in sunlight. High concentrations of O3 and PAN often build up where there are many automobiles.
* Nitrogen oxides - Automotive exhaust is probably the largest producer of NO. Oxides of nitrogen are also formed by combustion at high temperatures in the presence of two natural components of the air; nitrogen and oxygen.
* Particulates are small (<10 microns) particles emitted in smoke from burning fuel, particular diesel, that enters our lungs and cause respiratory problems.
* There is up to a 60 percent reduction in street level particulates with trees.
* In one urban park (212 ha.) tree cover was found to remove daily 48 lbs particulates, 9 lbs nitrogen dioxide, 6 lbs sulfur dioxide, and 2 lb carbon monoxide ($136/day value based upon pollution control technology) and 100 lbs of carbon.
* One sugar maple (12" DBH) along a roadway removes in one growing season 60 mg cadmium, 140 mg chromium, 820 mg nickel, and 5,200 mg lead from the environment.
Planting trees and expanding parklands improves the air quality of Los Angeles County. A total of 300 trees can counter balance the amount of pollution one person produces in a lifetime.
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