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Identifying mystery rotten egg smell attacking SF this week

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San Francisco fog turned yellow by the sunset.
Try not to inhale.
The Vine Studios

It sounds like the setup for a joke, but apparently more than 50 people on Wednesday really did report a mysterious and overpowering odor of rotten eggs across the city.

It wasn’t a gas leak, it wasn’t a chemical or oil spill at sea, and it wasn’t the Chevron refinery acting up.

Which is all great news, but that leaves the lingering (literally—some people are still smelling it) mystery of what it actually was?

Some people will tell you that the mysterious smell of rotten eggs mean your house is haunted. So there’s that.

On a slightly less outlandish note, mysterious odors are sometimes simple mass hysteria: One person kinda-sorta thinks he or she smells something, and within minutes the mistaken impression spreads.

But assuming there was a natural, material source for the weird affliction, it turns out there’s a lot of precedent to consider.

For whatever reason, mystery waves of rotten egg smell are quite common in coastal cities.

Andrei Stanescu

In 2012, a similar odor outbreak in LA turned out to be the visiting stench of the Salton Sea, pushed north by a major storm.

Just a few months later the smell was back again, this time in the Huntington Beach area. The likely culprit: ships passing in the night. That is to say, oil tankers, letting off a little gas nearby.

In Mountain View in 2009, that egg smell wafted up after a mass algae bloom and die off in the ponds near Shoreline Park.

The smell settled in Seattle in early 2015, possibly a case of flooded rivers and quirky microclimates teaming up to trap odors in the lower atmosphere.

(Meanwhile, the nearby city of Tacoma, Washington is so often afflicted that the odor qualifies as a kind of local landmark. The probable cause there is industrial.)

In 2014, Icelandic volcanoes vented egg stink across the whole of Scandinavia.

That same year, Moscow officials blamed a leak at an oil refinery for similar phenomena. (Again, Chevron says they’re clear in Richmond.)

On the other hand, sometimes the mystery endures longer than the smell: It’s still not clear what’s blighting the suburbs of Melbourne, Australia.

In short, if you live anywhere near a significant body of water, sooner or later this distinctive but strategically general smell will probably strike.

Although, at least one running theory about San Francisco’s latest odor episode finds not the ocean but the desert at fault.

Seismic fault, that is, as ABC7 speculates that earthquakes in Nevada may have unleashed the smell.

There’s no word on what their source for that notion may be. But stranger things have happened.