At 12:27 pm today (Tuesday, August 14), the National Weather Service issued an Air Quality Advisory, which is in effect until noon tomorrow (Wednesday, August 15). Their advice? The air sucks right now, as you can probably tell by looking out your window. Smoke from wildfires in Washington State has been drifting into the Portland area, and light winds will keep it coming our way until tomorrow, when conditions should improve.
You can also take a look at the current air quality index, calculated by the DEQ and the Oregon Health Authority. As of 1 pm today (see image above), we are at a deep red "Unhealthy," which sounds awful, but keep in mind that it could be worse: there's the bruised-violet "Very Unhealthy" ranking, before it maxes out at clotted-blood "Hazardous," at which point we all cower inside and take deep hits directly from our air purifiers.
Portland Parks & Recreation issued a press release stating that today's programs are continuing as planned, and outdoor pools are currently open. But they're moving some of their programs indoors, if possible, and will post updates on Portland's Inclement Weather web page.
So basically, stay indoors if you can, and if you're going outside, don't exert yourself too much. If you've got plans to run a marathon today, keep your eye on any updates to the air quality index. If the map looks like red wine's been spilled on it, maybe reconsider.