County health officials are warning residents with compromised health to limit their exposure to the smoke around the Pima County area, although air-quality monitors are not picking up particularly high levels of pollution.
The worst pollution levels were seen Monday morning in the Green Valley area - where they came in at 2.5 times the normal levels for fine-particle pollution - but those numbers had stabilized by the afternoon.
Raymond McLeod, a meteorologist with the National Weather Service in Tucson, said southerly winds are bringing in smoke from the Murphy Fire, which is burning south of Tucson near Tubac. The wind patterns aren't expected to change in the next couple days, he said, so as long as the fire is burning, Tucsonans may continue to have hazy conditions.
The smoke is going to be worse in the mornings, he said, since inversions trap the smoke low to the ground. A resident in Sonoita estimated the visibility Monday morning at two miles, he said, although Davis-Monthan Air Force Base and Tucson International Airport did not report any restrictions to visibility.
As the day heats up, the smoke will get pushed up into the upper atmosphere, he said. Gusty afternoon winds will also help break up the smoke, he said.
Although the Tucson Fire Department and the county Health Department did not report any uptick in respiratory-related calls, public-health officials are worried about particulate matter, the often invisible particles of dust that float in the air.
The smallest of them, measuring 2.5 micrometers, are the worst. Only a 30th as thick as a human hair, they can slip past the body's natural defenses, such as mucus and nose hair - and lodge deep within the lungs.
The U.S. Department of Agriculture estimates as much as 90 percent of particles in wild-land fire smoke are within the fine-particle size. They're so small, they can also stay in the air for days or weeks and can travel hundreds of miles.
The Environmental Protection Agency has set a health standard of no more than 35 micrograms per cubic meter, based on a 24-hour standard. Air-monitoring systems measured 70 in the Green Valley area at 9 a.m., although measurements stabilized by the following hour. So far, there has been no exceedance of the 24-hour standard throughout the course of the fire.
Susan Jones, the administrative assistant for the Green Valley Community Coordinating Council, said the smoke was thick enough that she couldn't see the mountains over the weekend. And while the wind pattern seemed to have shifted in the afternoon, she described Monday morning as "pretty odorific." Still, she said, the phone calls she had anticipated didn't materialize throughout the day.
In Tucson, the highest reading came midmorning at 40 on the south side near C.E. Rose Elementary School. Otherwise, most readings failed to show elevated levels.
Environmental Quality spokeswoman Beth Gorman acknowledged that may seem counterintuitive, given the visibility of the smoke, but suggested the particles might be larger than what the department is measuring, or they may be higher in the atmosphere than the monitoring stations, which are at ground level.
"It's not a panic situation," she said, but suggested those with heart or lung disease, or those sensitive to particulates, should reduce their exposure. That means trying to avoid exercising or working outside, or at least limiting exertion when they are outside. Air conditioning is often preferable to evaporative cooling to reduce smoke exposure. For healthy adults, exposure to elevated levels for small periods of time shouldn't result in significant health impacts.
Otherwise, for a general rule of thumb, she said: "Even though you're seeing this in the air, if you don't smell the smoke, the chances are you're not at risk. It doesn't seem to be pervasive across the community."
If nothing else, said meteorologist McLeod, the sunsets should be "kind of interesting."
Just to be on the safe side, maybe watch them from behind your (closed) window.
Contact reporter Rhonda Bodfield at email@example.com or 573-4243.