With the fog, there's less light hitting the sensor, so the camera's going to capture noisier images. Most cameras will automatically apply noise reduction algo

With the fog, there's less light hitting the sensor, so the camera's going to capture noisier images. Most cameras will automatically apply noise reduction algorithms, and additional noise reduction can be done in Lightroom/Photoshop - when applied liberally, this can result in an appearance that almost looks like an oil painting, as clusters of similarly colored areas are smeared together.