Worst Air Quality In World Is In Pacific Northwest

Smoke from wildfires is causing a thick smog in the 
Pacific Northwest. Here, it's obscuring the Seattle skyline
this morning 

 When we think of the Pacific Northwest, places like Seattle and Portland, we think of pretty clean air. 

The rain cleanses the air, and breezes off the ocean flush pollution away. 

Not lately.  The two worst cities in the world for air pollution over the past day or two were Seattle and Portland.

It was even worse there than cities that have notoriously bad air, like Beijing, Lahore and New Delhi.

Forest fires and a temperature inversion are to blame. A fire east of Portland has been burning since September 10 and continues to belch smoke. Other, smaller fires are contributing. Many of these started in a record heat wave that struck the region last week and weekend. Seattle hasn't seen any rain since June 9, and endured its driest summer on record.

Wildfires can cause horrible air quality any time they burn. It can be worse in the autumn.  Smoke and pollution can get trapped under a temperature inversion, in which a layer of warm air aloft acts as a lid that prevents the smoke from dispersing. 

In the summer, the sun angle is steep and the heat from the sun is powerful.  The heat from the sun can create updrafts that break up the inversion and let some of the pollution to escape. 

A lower sun angle in autumn and winter means the sun might not be powerful enough to break the inversion. So the particulates and smoke and other gunk keeps piling up. The air gets downright dangerous. 

The Puget Sound Clean Air Agency went as far yesterday to urge everyone to stay indoors if possible because the air was so bad. 

In the past, autumn inversions and air pollution have proven deadly. Among the most famous cases was the Denora, Pennsylvania smog on October 27-30, 1948.  A temperature inversion produced a persistent fog, and the steel mills in the area added choking clouds of smoke to the mix.  The smog was trapped under an inversion.

It became so dangerous that 20 people died.  Hundreds more were hospitalized and people with cardiac and respiratory issues were urged to evacuate. Rain arrived on October 31 and dispersed the smog.  Some experts say if the smog lasted a day or more longer, perhaps 1,000 people could have died.

The Denora smog disaster helped get the ball rolling to improvements that led to the Air Quality Act, which greatly reduced U.S. air pollution.

Much like in Denora, a series of rain storms is expected to hit the Pacific Northwest, starting Friday.  The rain and west winds off the Pacific will flush the bad air out, and contribute toward extinguishing the forest fires plaguing the region.