A 400-mile-long fog has blanketed California's Central Valley for weeks. Scientists and meteorologists say the conditions are ripe for such persistent cloud cover: an early rainy season, cold temperatures and a stable, stationary high-pressure system.
But take a stroll through X, Instagram or TikTok and you'll see that not everyone is so optimistic.
People report that the fog has a strange consistency and that it is strewn with black and white particles that appear unusual. They call it “mysterious” and emphasize the name “radiation fog”, which is a scientific description of such natural fog phenomena, not an indication that they carry radioactive material.
User X, who goes by Wall Street Apes, posted a video of a Northern California man running his finger through fog condensation on the grille of his truck. His finger rises, covered in white.
“What is this… right here?” the man says as the camera zooms in on his finger. “There's something in the fog that I can't explain… Check it out… you're all crazy… What's going on? They've got asbestos in there.”
Another user, @wesleybrennan87, posted a photo of two aircraft contrails crossing the sky through a gap in the fog.
“For those keeping an eye on the thick Thule (Radiation) fog in the California Valley, it cleared for a moment today just to see that they were quite active above our heads…” the user wrote.
Scientists confirm that there is something in the fog. But what it is and where it comes from, they say, is depressingly commonplace.
The Central Valley is known to have some of the highest levels of air pollution in the country.
“Fog is very sensitive to pollutants,” said Peter Weiss-Penzias, a fog researcher at the University of California, Santa Cruz.
“Fog droplets have a large surface area and are suspended in the air for quite a long time – days or even weeks – so during this time the water droplets can absorb a disproportionate amount of gases and particles, otherwise known as pollutants,” he said.
He said that while he hasn't done any analysis of the Central Valley fog during this latest event, it's not hard to imagine what might be lurking in the droplets.
“It could be a whole alphabet soup of different things. With all the agriculture in this area, the industry, the cars, the wood smoke, there's a whole bunch of contenders,” Weiss-Penzias said.
Reports of the mist turning into a jelly-like goo when left to sit aren't entirely surprising either, he said, given all the airborne biological material – fungal spores, nutrients and algae – floating around, which can also stick to Velcro-like water droplets.
He said the good news is that while the main way people are exposed to the material is inhalation, the mist droplets are relatively large. This means that when they are inhaled, they don't go too deep into the lungs – unlike the particulate matter we inhale on sunny, dry days. This stuff can penetrate lung tissue.
Ingestion is a big concern, he said, as fog covers plants or open water tanks.
So be sure to wash your vegetables and anything you leave outside that might be eaten later.
Dennis Baldocchi, a fog researcher at the University of California, Berkeley, agreed with Weiss-Penzias' assessment and said the storm system forecast to arrive this weekend will likely push out the fog and free the valley of its cold, muddy shawl.
But if a high pressure system returns in the coming weeks, he won't be surprised to see the region shrouded in fog again.
