David South and Forest list readers: This is an interesting issue. I recently had the opportunity to do some literature research in this field, and was surprised to learn that volatile organic carbon emissions from natural vegetation contribute significantly to the production of photochemical smog. In my part of the world, poplars are probably the greatest contributor both in terms of their specific emission rates, but also by virtue of their tremendous abundance (especially trembling aspen) in the boreal forest. What I found interesting in the original post was President Reagan's statement that 80% of all air pollution in the US came from vegetation. While Reagan probably would have been correct to say that 80% of the photochemical smog is derived from VOC emissions from vegetation, it is debateable whether so much of the air pollution comes from that source. This is not just semantic 'air-splitting, since Reagan's original statement glosses over a real problem. Where there are serious pollution problems, i.e., in and around large cities, the density of trees is limited by the amount concrete and asphalt laid down to accomodate cars and their people. On their own the trees would contribute to smog production, but not usually in noticeable quantities. The only place I know of which has a noticeable natural smog problem is the Great Smoky Mountains in the eastern USA. As I understand it, the "smoke" in the Great Smokies is photochemical smog derived from emissions of the hardwood forests covering these mountains. In human-dominated environments that suffer from smog, the finger has fairly convincingly been pointed at industrial sources and auto exhaust as the major causes. Now (finally) to my point. When photochemical smog causes health and quality of life problems for people and other inhabitants of cities, then there is an air pollution problem. When photochemical smog has little discernable effect on us or other things we care about, then can we say that the air is polluted, especially if the source is natural vegetation? It reminds me of the definition of a weed: something growing where you don't want it to. Smog is pollution if it causes you problems. The point (really finally!) is that saying 80% of air pollution comes from vegetation suggests that vegetation causes 80% of our air pollution problems. This is clearly deflecting attention and action from the source of the problem, which is that human sources such auto emissions are the major source of the air pollution problem. Changing the tree species that line the streets might help, but the problem won't go away until the real source of the problem is tackled. There's my two-bits worth. I hope this stimulates some commentary. - Jim Stewart > From: David South <dsouth@SOFSERV.FORESTRY.AUBURN.EDU> > Subject: Re: Hardwood trees cause air pollution > Dear Readers; > Dr. Harley at the National Center for Atmospheric Research has said that > many hardwood > species are huge emitters of hydrocarbons (see below). This supports > President Reagan's statement that > "Approximately 80% of our air pollution stems from hydrocarbons released by > vegetation,...." > > Since the volume of hardwoods in Alabama has increased by 85 percent since > 1952, I assume the emission of hydrocarbons by hardwoods has also increased > by 85%. If a few sweetgum and sycamore trees cause air quality problems in > cities in California, how much air pollution would 57 million cubic meters > cause in Alabama? > James D. Stewart Telephone: (403) 492-6827 Dept. of Renewable Resources Facsimile: (403) 492-1767 University of Alberta E-mail: james.stewart@ualberta.ca
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