Several locations around the Northwest are experiencing poor air quality….with some locations having particle concentrations comparable to recent wildfire events.
But this time it’s not a wildfire. It’s woodsmoke plus SuperInversion. Puget Sound Clean Air Agency has imposed a Phase 1 Burn Ban.
Let’s start by looking at the air quality information from the PurpleAir network (below) this morning. Green is good air quality, yellow is declining, orange is worrisome and red/purple is unhealthy.
Air quality is moderate south of the Sound, but air quality has deteriorated severely around Spokane, northeast WA, and around Bend Oregon.
The source of the smoke is obvious: mainly smoke from firewood for heating. In parentheses, a highly renewable energy source.
Traditionally, the main air quality problem in the Northwest has been caused by wood smoke rather than summer wildfires. But wood smoke has subsided as a problem as more people use natural gas fireplaces/fireplaces and air quality agencies (such as the Puget Sound Clean Air Authority) issue and enforce burning bans in threatening situations. Wider use of natural gas has helped to clean up our winter air. And rising oil and gas costs have also stimulated the use of wood.
We are currently in a threatened position as a strong inversion of increasing temperature with height has developed over our region. Inversions are very stable features that act as caps on the lower atmosphere.
Above SeaTac Airport at 7 a.m. this morning, temperatures rose from 38-39F just above the surface (and even lower at ground level) to 49-50F at about 2000 ft. A strong low temperature inversion.
At Quillayute, on the Washington coast, temperatures rose from 1 to 13 degrees Celsius on a similar layer near the surface (see chart below). That’s about 22F warming up in a few thousand feet. OH. Mama Mia… that’s a powerful reversal!
So we have cold weather that stimulates people to increase wood burning and an inversion that covers the lower atmosphere, allowing pollution levels to increase.
Why do we have such a strong reversal? Blame it on the strong, persistent high pressure pointing to the ridge above us (see upper-level map for this morning below).
High creates sinking air at high altitude that prevents clouds from forming. With no clouds, the surface can effectively emit infrared rays into space, cooling the surface. Like having a refrigerator coil on the surface.
Subduction from high altitude causes air to compress and warm at medium altitudes. This speeds up the reverse even more!
And our nights are also very long now, allowing for more surface cooling.
Future prospects? The poor air quality is expected to continue (or even worsen) this week.
