Stricter Air Standard Pending

By Tony Davis, ARIZONA DAILY STAR

New rules could hit our ‘brown cloud’

When Liz Ownbey of the Tucson Mountains sees the wintertime brown cloud of pollution, she wants to don an oxygen mask before driving into the city.

When fellow Tucson Mountains resident Robert Nelson sees the same cloud of smoke, haze and vehicle exhaust, he’s glad he doesn’t live under it.

Starting this month, the brown cloud with its yellowish tinge should once again become as much a fixture in Tucson’s holiday season skies as turkey and dressing on the dinner table. In the winter, it can hover as low as 500 to 600 feet above ground. That often makes it less obvious to urban dwellers living directly under the cloud, but clearly visible to foothills and far suburban residents whose homes rise above it.

A year-round phenomenon caused by temperature inversions that trap pollutants close to the ground, the brown cloud generally grows thicker and lasts longer during cooler times, state and county health officials say.

While it’s hardly a health crisis compared with the more polluted skies of Phoenix, Salt Lake City and Denver, Tucson’s brown cloud still carries potential risks for people with asthma, bronchitis or other respiratory diseases, according to the Pima County Department of Environmental Quality.

The county’s air hasn’t violated any federal pollution standards since 1999. But Tucson’s skies might soon start getting the county in trouble with the federal government.

In late December, the Environmental Protection Agency plans to propose new, most likely stricter health standards for particulates. They’re tiny particles of soot from diesel-burning trucks, dust from dirt roads and construction activity, fireplaces, agriculture and other sources.

The agency won’t comment on the proposal before releasing it. An EPA staff report said last June that the current standards for coarse and fine particles aren’t strict enough to protect public health.

Tucson’s air quality appears well within the potential limits discussed in that paper for smaller, fine particles. But county officials say reports they’ve gotten from EPA officials suggest that the new standard for coarse particles may be tight enough that the county would exceed it several times a year. The EPA plans to approve the final standards next September.

The cloud itself is an aesthetic and health issue, said Beth Gorman, a program manager for the county environmental agency.

“The reason that a lot of people come to Tucson is for the mountain views,” Gorman said. “I also know from calls I get that people with respiratory problems are more sensitive to pollution than others.”

The county gets a handful of calls each winter from people complaining about fireplace smoke. It also gets three to five calls a month in the winter from people with respiratory ailments about the air quality in general, Gorman said. Those calls usually come on overcast days when smoke is trapped closer to the ground, Gorman said.

Some relief will be on the way in the next two years, say state Department of Environmental Quality officials. The EPA will OK tougher standards on sulfur content in diesel fuel next year and on diesel engines’ makeup in 2007.

Together, they should reduce vehicle diesel emissions that are a key source of particulates in the cloud, said Steve Owens, the state agency’s director. That should reduce the cloud’s rate of growth and could decrease its size, Owens said.

The most recent analysis of Tucson’s urban haze, from the mid- 1990s, found that about half of the brown cloud’s pollution comes from vehicle exhaust, the state agency says.

“It’s an unfortunate consequence of growth in many respects,” Owens said. “The biggest components of the brown cloud, fine particulates, diesel exhaust and dust, are a byproduct of growth and/ or cars driving more miles for longer periods of time each day.

“The farther out you have development and the farther people live from their places of businesses and shopping, the more miles they drive and the more exhaust.”

Augusta Davis, a Tucson Mountains resident, said she can see the cloud once or twice a week from her home and is frustrated that it sometimes blocks her view of all but the highest points in the Rincon Mountains across the Tucson valley.

“If there’s a brown layer in the air, to me, it’s a health problem,” Davis said. “We’re breathing that stuff.”

Here’s what you’ll find inside the brown cloud

* Motor vehicle exhaust: 45 percent

* Dust from dirt roads, construction activity and other sources: 19 percent

* Ammonium nitrate, formed by conversion of gaseous oxides of nitrogen: 9 percent

* Wood-burning ash: 8 percent

* Nitrogen dioxide, also from vehicle exhaust: 6 percent

* Ammonium sulfate, formed by conversion of gaseous oxides of sulfur: 3 percent

* Natural light extinction – the diminishing of light by natural atmospheric conditions: 9 percent

* Unknown: 1 percent

How the brown cloud forms

* In a temperature inversion, cold air that usually stays above warm air in the atmosphere sinks overnight and traps air pollutants close to the ground.

* Those pollutants form a thick layer that hangs over the valley.

* When cold air sinks and warm air sits above a valley such as Tucson’s, the various air masses don’t mix, the valley stays cold and the pollution sticks around.

* The five mountain ranges ringing most of Tucson aggravate the brown cloud by blocking winds that could blow the pollution elsewhere.

* In the winter, the sun rises later and cold air hangs on longer, delaying the breakup of the inversion and the brown cloud.

Sources: National Weather Service, Pima County Department of Environmental Quality and “Tucson Urban Haze Study Final Report,” from the mid-1990s, by the state Department of Environmental Quality.

* Contact reporter Tony Davis at 806-7746 or tdavis@azstarnet.com.