Wildfire smoke thick enough to briefly give Portland the worst air quality of any major city in the world Wednesday morning is choking Washington County, and the National Weather Service says it won't clear Tigard and Tualatin until late Thursday night.
The NWS air quality alert runs through 11 p.m. Thursday, Aug. 6, covering Washington County. Air quality monitors in nearby Beaverton and Hillsboro recorded readings as high as 138 on the Air Quality Index as of Wednesday, Aug. 5, placing the area in the "unhealthy for sensitive groups" range. No separate AQI monitor serves Tigard or Tualatin specifically, but both cities sit in the same eastern Washington County smoke zone.
Oregon's Department of Environmental Quality issued a separate advisory covering the Portland metro area, including all of Washington County, that remains in effect until further notice, according to oregonsmoke.org.
What's causing the smoke
The primary culprit is the Grasshopper Fire, burning 12 miles east of Government Camp in the Mount Hood National Forest. Sparked by lightning on July 23, the blaze had grown to 39,439 acres at just 20% containment by Wednesday. Three other large fires are adding smoke: the Rowe Creek Complex near Fossil (329,012 acres, 62% contained), the Shingle Fire near Mitchell (70,806 acres, 50% contained) and the Bench Fire near Warm Springs (67,079 acres, 84% contained).
An offshore wind pattern called a West Coast Thermal Trough is funneling smoke westward through the Columbia River Gorge and into the Willamette Valley, according to NWS Portland forecasters. Oregon DEQ notes smoke concentrations tend to worsen in evening hours as temperature inversions trap particulates near the ground.
Health risks
Dr. Ian Smith, head of pulmonary medicine at St. Charles Health System, said the fine particles in wildfire smoke, known as PM 2.5, are small enough to pass through lung tissue and enter the bloodstream.
"These particulates are small enough to get into the bloodstream, and that's what can cause people to have that really yucky feeling … where they feel really fatigued and just different," Smith told the Valley Times.
Smith said the resulting inflammation is similar to what alcohol does to the body and can increase the risk of heart attack and other cardiac events. People with asthma, COPD, heart disease or diabetes, children, adults over 65 and pregnant individuals should avoid all outdoor activity while AQI remains above 100.
How to protect yourself
Oregon DEQ recommends keeping windows and doors closed, running HVAC systems on recirculate mode and using a HEPA air purifier or a DIY box fan fitted with a MERV-13 furnace filter. If you must go outside, wear an N95 or P100 respirator. Cloth masks do not filter PM 2.5.
Washington County opened a 24-hour emergency shelter at the Just Compassion Access Center, 12264 S.W. Hall Blvd. in Tigard, but it closes at noon Thursday, Aug. 6. The Tigard Public Library at 13500 S.W. Hall Blvd. and Tualatin Public Library at 18878 S.W. Martinazzi Ave. are both open as cooling and clean-air spaces during regular hours Thursday (10 a.m. to 8 p.m.).
When will it clear?
NWS forecasters expect onshore Pacific flow to return late Thursday into Friday, Aug. 7, pushing smoke back east of the Cascades. The weekend forecast calls for cleaner air and temperatures easing into the low-to-mid 80s.
Residents can check real-time AQI readings at fire.airnow.gov or oregonsmoke.org. Tigard residents can also sign up for emergency alerts through the city's Everbridge notification system.
