What is the heavy particle fog being reported in various places in the US and UK?

"The dense fog alert issued by the National Weather Service could, however, help debunk such conspiracy theories with a scientific explanation.

Although the particles may seem unusual, fog is a visible aerosol comprising ice crystals or water droplets suspended in the air near the Earth's surface. If one shines light into a layer of fog, the particles become visible.

Fog also has the affinity to trap and absorb the polluted air on Earth's surface which could perhaps help explain the chemical smell. In humidity, smells become more potent as water droplets allow the odor-causing substances to remain concentrated and linger for a while."

https://www.msn.com/en-us/science/environmental-science/mystery-thick-fog-sweeps-across-the-us-with-burning-chemical-smell-in-the-air/ar-AA1wRYe4