I saw this article at BoingBoing, and had to look it up.
From Wikipedia:
The Aroma of Tacoma, also known as the Tacoma Aroma, is a putrid and unpleasant odor associated with Tacoma, Washington, United States.[1] The smell has been described as similar to the odor of rotten eggs.[2] The odor is not noticeable throughout the city, but is rather concentrated in the Tacoma tideflats and is frequently smelled by motorists traveling that section of Interstate 5.[2]
That is part of it, also the Puget Sound is kinda like pushing everything to the south with the weather and the tides.
Thankfully it’s better these days. It was absolutely dreadful in the 70s and 80s