Ronald Reagan had them rolling in the forests last year when he fingered trees as a chief culprit in the natin's air pollution battle. In one of his most widely reported -- and widely ridiculed -- campaign statements, Mr. Reagan proclaimed that "growing and decaying vegetation in this land are responsible for 93 percent of the oxides of nitrogen," expanding on an earlier statement in which he implied that trees were a major source of air pollution.
"Simplified," "naive," and "Neanderthal," responded the scientific community.
But also close to home. In exaggerated and misleading terms, say scientists, Reagan touched on a question that has long concerned many researchers, and which has become a highly politicized topic in the ongoing debate over how strictly man-made polluters should be regulated:
Do plants play a part in making air pollution?
No one knows for sure, but lots of people would like to find out. The way industry sees it, if vegetation does contribute to pollution, then the government's focus on controlling man-made polluters like cars and factories coudl be placing an unfair burden on business. The way air quality regulators see it, such proof would mean cracking down even harder on man-made polluters, because there's no way to slap an emission control device on Mother Nature. And the way scientists see it, well, they just want to know.m
"What pollutants have I no control over? That's critically important in terms of complying with the Clean Air Act and in drawing up state plans for compliance," says Carleton Scott, director of environmental sciences for Union Oil.
One thing scientists do know is that plants produce plenty of hydrocarbons, one of the key ingredients in the chemical reaction that produces smog. In fact , it is generally accepted that plants produce more hydrocarbons than do man-related activities -- by as much as 0.5 to 20 times more on a global basis, according to one estimate.
Other researchers respond, however, that such a comparison is completely misleading and generally has been used as a "whipping boy" in the whole man vs. plant debate. Althoughit is possible to put a plastic bag over a tree limb and measure the emissions of hydrocarbons, scientists so far have found it virtually impossible to find any traces of those same hydrocarbons in the urban air mixture. And therein lies the scientific dilemma: Where do these biogenic, or plant-produced, hydrocarbons go, and what do they do?
"It's still an open question," explains Dr. R. A. Rasmussen, a professor of air chemistry at the Oregon Graduate Center and a pioneer in this area of research in the early 1960s. "They are there, they exist. You can measure them at the source . . . . yet you go out to measure them in the atmosphere and they seem to be gone."
Many scientists agree, however, that what evidence there is seems to indicate vegetation is not a significant contributor to air pollution in urban areas. But because of the many scientific unknowns, research will continue at both the university and federal level in an attempt to better understand the effects of biogenic hydrocarbons in the atmosphere.
In addition, says Dr. Marcia Dodge, an EPA research chemist, the work has a political dimension. By searching for answers to the biogenic issue -- a search that intensified in 1978 with the publication of a controversial article alleging a connection between vegetation and ozone concentrations -- air quality controllers will protect themselves from industry charges that government unfairly imposes air quality standards when it does not know the impact of uncontrollable sources like vegetation.
"We can't have all the research being done by the other side," she says.
In at least one air quality basin, the San Francisco Bay Area, officials are moving to counter such industry broadsides. In the local plan now being drawn up for submission to the state as part of its EPA-required plan to control pollution, Bay Area experts are trying to calculate how much of the basin's ozone problem is caused by vegetation and how much by man-made sources.
"There's nothing we can do about controlling biogenics," says Ron Wada, air quality program manager for the Association of Bay Area Governments. "The question for us is that we need to take into account their effect, so that we know that what we say will happen as a result of the controls we propose, will happen."
Overall, however, many scientists agree that biogenic research is only one part of the very complex problem of air pollution. And, they say, the most important way to control pollution is still by regulating mobile and stationary man-made sources.
"It's bit of a spurious issue," fumes one Los Angeles air quality official. "We have a lot of work to do before we get down to trees.
"It's hard to stand here in LA and say that trees are causing all the pollution," he continues, "not with 7 million cars and 40,000 stationary sources. It's not credible. Not even the President of the United States can get away with saying it."