Smoke will return to Corvallis this weekend due to continuing wildfire-prone conditions, posing potential health risks.

The Willamette Valley has experienced smoke pollution over the past week due to a recent increase in regional fire activity, according to the United States Department of Agriculture Forest Service. In a morning brief, the Northwest Interagency Coordination Center reported two new large fires, one contained large fire and 16 uncontained large fires, including 14 in Oregon, as of the morning of September 1.

A fire is considered “large” if its size and intensity is great enough that its behavior is determined by interactions with weather conditions above the surface, according to the National Wildlife Coordinating Group website.

“Weather conditions primarily drive the fire activity and we have had hot, dry, weather patterns through the state for the past several weeks,” said Claire McGrew, assistant chief deputy at the Oregon Office of the State Fire Marshal.

McGrew said response teams are currently working hard to mitigate the effects of recent wildfires. Depending on the location, these teams can be made up of local fire departments, private contractors and the Oregon Department of Forestry among others groups.

While much of the smoke in the Willamette Valley cleared by September 1, Katherine Benenati, a public affairs specialist with the Oregon Department of Environmental Quality, said that smoky conditions are expected to return to the Willamette Valley.

In its September 1 smoke forecast, the USDA Forest Service predicted that dry conditions accompanied by near record-breaking temperatures will develop in much of the state over Labor Day weekend. These conditions create high potential for continued fire activity, which will likely bring smoke to the Willamette Valley, but may be more highly concentrated further south.

Benenati suggested that concerned residents should pay attention to Air Quality Index monitors, one of which is located in Corvallis. This index uses a color code from green for ‘good’ through yellow, orange, red, purple and magenta for ‘hazardous’ to reflect local air quality. The AQI measures the content of pollutants in the air including particulate matter, which is the main harmful component of wildfire smoke.

Particulate matter refers to a broad assortment of solid or liquid particles that mix into the air, ranging from relatively large particles, like dust and soot, to particles that are imperceptible to the human eye, according to the Environmental Protection Agency’s website. These particles can cause health problems in human respiratory and cardiovascular systems, and they can also aggravate existing heart and lung problems.

“If you’re in an unhealthy group—that would be like elderly, children, if you’re pregnant, if you have heart or lung disease—then you want to start taking precautions when the air quality is at orange, or ‘unhealthy for sensitive groups,’” Benenati said. “When you get up to ‘unhealthy’ those groups should avoid all physical activity outside, and then everybody else should avoid prolonged or heavy exertion outside.”

Taking into account climate change, increases in wildfire activity will take place in hot, dry areas, said Beverly Law, an Oregon State University professor in the Department of Forest Ecosystems and Society. As a result, Oregon will likely not experience any drastic increases, based on current observed trends.

Law added, however, that while significant increases in wildfires are not present in current data, Oregon summers have become hotter and drier since the 1970s. If that trend continues, wildfire activity could increase in the future.

“(With) aboveground biomass mortality in Oregon, 86 percent of it is due to harvest removal, 9 percent is due to beetles and 8 percent of it is due to fire,” Law said. “So that puts into perspective what is really impacting forests the most in Oregon.”

Biomass mortality, which measures the mass of all organic matter lost, is used instead of a count of lost trees to get more representative data on the impact of a fire.

Law added that forest fires—which predominantly involve the burning of organic matter near the forest floor, rather than trees themselves—produce smoke containing mostly moisture and particulate matter that does not enter the upper atmosphere. As a result, forest fires do not have a large impact in terms of greenhouse gases. However, this particulate matter is the main cause of respiratory and other health problems.

“We’re getting a lot of questions about what precautions people should take, what areas are affected,” Benenati said. “Keep an eye on the air quality index, those monitors are up on the Oregon smoke blog, they’re on (the Department of Environmental Quality’s) website (and) there is an air quality monitor in Corvallis.”