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E-mail StoryDispute persists over trees as polluter
| Sunday, Sep 17 2006 11:51 PM
Last Updated: Sunday, Sep 17 2006 11:51 PM
Politicians won’t touch it, air regulators hate to admit it and tree advocates would rather not discuss it, but here’s the ugly truth: Plants are a thriving source of air pollution.
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Tree emissions dwarf what comes from dairy cows. Dairies are pegged as major polluters, but plants out-emit dairies by more than 30-to-1 statewide. California’s trees release some 2,000 tons of smog-forming gases daily. Dairies produce 60 tons each day.
All of it is harmless until fumes from automobiles and other engines mix in, creating summer smog.
Because trees also have benefits, such as sucking up carbon dioxide and providing shade, researchers haven’t figured out whether they are overall good or bad for pollution.
Nevertheless — due in part to jurisdiction and politics — dairies, not trees, are a primary target of regional air regulators.
No joke
“(Former President) Reagan got laughed at for talking about (tree emissions) 30 years ago and a lot of people are afraid to talk about it now,” said J.P. Cativiela, a spokesman for the dairy industry group Community Alliance for Responsible Environmental Stewardship.
That’s not to say dairies shouldn’t be regulated, he said, but “sometimes we can get a little bit ridiculous when we think about pollution sources.”
In the San Joaquin Valley, where dairies are concentrated, plants out-emit dairy cows by more than five to one.
“Industry does bring this up,” said Stephen Shaw, an air quality specialist with the regional air authority known as the San Joaquin Valley Air Pollution Control District. But regulators “consider natural resources something we can’t do anything about,” he said.
The district can control emissions from dairy cows, wineries, refineries and other non-vehicular sources. Models show reductions in these sectors help air quality despite what’s released by plants, district staffers say.
Business advocates often bristle at being the focus of air police. New rules can mean big money.
Existing dairies dodged expensive equipment this summer, largely because regulators’ understanding of dairy emissions changes with each new study. Until more research is done, dairies are allowed to make procedural changes to reduce emissions rather than invest in new equipment.
Was Reagan right?
Plant emissions shed light on Ronald Reagan’s infamous observation that trees pollute more than cars on the road. His statement dabbles in fact — plants outdo motor vehicles when it comes to one specific emission variety — but the larger picture is more complicated.
Automobiles, power plants and engines produce a range of pollutants, one of which sullies the air year-round. Some of them are toxic in themselves, but they also mix with benign gases to form pollution.
On the other hand, raw automobile emissions also “quench” certain kinds of pollution, said Don Hunsaker, a supervisor at the valley air district. It’s another paradox of air chemistry, he said.
“People throw their hands up and say ... why even bother,” he said. But “the problem’s too big. It’s a matter of working harder to (meet) the standards.”
The notion of plants as polluters has “really hurt” local efforts to encourage tree planting, said Dana Karcher, executive director of the Tree Foundation of Kern.
Trees absorb pollution, she said. Their shade creates a cooling effect, which keeps polluting gases from evaporating and slows down smog’s chemical reaction. A well-placed tree can also minimize the need for air conditioning fueled by polluting power plants.
“A shaded street or parking lot does more for air quality than micromanaging oak (trees),” she said.
The Center for Urban Forest Research in Davis is trying to quantify the benefit of trees. The think tank, which is affiliated with the U.S. Forest Service, is studying Sacramento’s canopy to figure out its net effect on air quality.
“There’s all sorts of ifs, ands or buts” when it comes to trees and air pollution, said Jim Simpson, a meteorologist with the center.
Tree species ooze emissions at vastly different rates, and whether those emissions contribute to smog depends on climate and the mix of pollutants already in the air.
With the right mix of trees in the right place, “I think they can be a net benefit,” Simpson said.
In the benefit column, Sacramento’s 6 million trees remove about 1,000 tons of pollutants from the air each year, according to the center’s research.
Trees do absorb carbon dioxide, but when trees die and decompose they release it again. The real carbon dioxide reduction is in prevention; Sacramento’s shade reduces energy use, keeping 83,000 tons of carbon dioxide from being released from power plants.
The detriment column is still a work in progress, Simpson said. State data show plants in Sacramento County produce about 10 tons of emissions each day.
The forest for the trees
The city of Bakersfield doesn’t account for air quality when it advises developers and residents on the kinds of trees to plant. Some trees that do best in Bakersfield’s climate, such as oak and sycamore varieties, are also active emitters.
“When we start picking on our greenery, I don’t know where we’re going to go then,” said Pat Denney, who supervises the city’s tree maintenance crews.
The city no longer employs an urban forester to oversee the mix of trees in Bakersfield. The city is in the process of counting up its trees, but the inventory will be used to track tree maintenance rather than plan future tree planting.
If someone were planning Bakersfield’s trees with regard to pollution, he or she should try to achieve a mix, said Greg McPherson, director of the Center for Urban Forest Research.
“It doesn’t mean you don’t plant native oak,” he said. You just make sure “you’re not kind of blindly planting trees that may in fact be high emitters.”
In other words, the botanical bouquet needs to be managed — something long sought by Karcher and other tree advocates. They want the city to write a long-range plan for its trees, one that could address pollution and the value of shade.
“If you have a plan, the rest ... will follow,” Karcher said.