A number of factors have combined to increase volatile organic compounds (VOCs) air pollution from trees faster than VOC pollution from humans has declined.
They calculated that vegetal sources of monoterpenes and isoprene rose by up to 17% from the 1980s to the 1990s – equivalent to three times the industrial reductions.
The three major contributing factors are the natural reversion of abandoned farm land to forested land, the invasion of sweetgum trees, and the growth of large forests of pine trees for lumber.
Princeton University post doc Drew Purves got to the bottom of the tree pollution problem.
Further studies at Princeton and the federal Geophysical Fluid Dynamics Lab at Princeton are using sophisticated computer models to estimate the changes in ozone caused by the changes in tree-produced VOCs. Purves noted that interactions between VOCs, NOx and ozone are complex -- some may actually lower pollution -- so it would be premature to base environmental policy on studies of VOCs alone.
Purves, a postdoctoral fellow, wrote the article in collaboration with Stephen Pacala, professor of ecology and evolutionary biology at Princeton, as well as John Casperson of the University of Toronto, Paul Moorcroft of Harvard University and George Hurtt of the University of New Hampshire. The article is scheduled to be published later this fall in the journal Global Change Biology.
The scientists conducted the study by analyzing data collected by the U.S. Forest Service, which measured and cataloged 2.7 million trees on 250,000 plots of land across the country. They calculated the VOC emissions for each tree and each plot and used their findings to map VOC levels nationally. The scientists compared survey data taken in the 1980s with those taken in the 1990s to determine how levels were changing over time.
They found that areas where farmland has been abandoned during the last century have early generations of trees that produce higher levels of VOCs than older growth forests. In the South, pine plantations used for their fast-growing supplies of timber have proven to be havens for sweetgum trees, which are major producers of VOCs. Indeed, virtually every tree that grows fast -- a desirable quality for forestry production -- is a heavy emitter of VOCs.
"It's just one of those biological correlations," said Purves. "What you want is a fast-growing tree that doesn't produce a lot of VOCs, but that doesn't seem to exist."
The truth is plain to see: Nature is dangerous and needs to be brought under greater human control so that we can have a safer and cleaner environment. This shouldn't be surprising. After all, where does typhoid come from? Nature. Where does the Ebola virus come from? Nature. Where do cholera, diphteria, malaria, and tuberculosis come from? Or tidal waves? Earthquakes? Rattlesnakes? Tornadoes? Floods? Avalanches? Black widow spiders? The asteroids that probably wiped out the dinosaurs? You already know the answer to all those questions. And what about air polluting volcanoes? They aren't operated by the petroleum industry.
Consider the irony for construction. If you build with concrete, steel, plastic, and other less natural materials you will reduce the need to plant trees and therefore fewer polluting trees will be planted.
Polluting trees also call into question the idea of using various kinds of biomass as energy sources. If we grow more stuff then that disgusting and dirty (hey, plant roots have dirt all over them) plant matter is going to release all kinds of pollutants into the atmosphere.
The findings also could raise questions about potential strategies for developing "green" fuels. One idea for cutting greenhouse gas emissions is to create "biofuels" from renewable tree plantations; however, these plantations may lead to increased ozone levels, the authors note.
What to do? Technology can provide the answer: plants used for biomass and trees grown for lumber need to be genetically reengineered to be less polluting. If better engineering designs can make cars less polluting then why can't better engineering clean up trees and other natural polluters as well?
Ronald Reagan came in for a lot of criticism when he warned of the dangers of letting trees run amok and ruin our air.
Noting President Ronald Reagan's notorious 1980 reference to trees causing pollution (Reagan said: "Approximately 80 percent of our air pollution stems from hydrocarbons released by vegetation."), the authors conclude: "The results reported here call for a wider recognition that an understanding of recent, current and anticipated changes in biogenic VOC emissions is necessary to guide future air-quality policy decisions; they do not provide any evidence that responsibility for air pollution can or should be shifted from humans to trees."
But obviously Ronnie was on to something. Where others have been lured into looking at towering Redwoods and seeing ancient stately majestic beauties reaching serenely into the sky Ronnie saw right through them like he saw through communist fronts. While the real effects of trees were invisible to the rest of us Ronnie clearly saw that trees were waging a silent war on Western civilization.
Update: One other point: The older trees in older forests pollute less. Tree population aging is a good thing.