A fog is produced from liquid droplets held in suspension. The larger droplet sizes are easier to be seen; the smaller droplets ULV (ultra-low volume) that range under 15 microns are mostly invisible. There are different droplet sizes:
Dry fog (5-15 micron Volumetric Mean Diameter)
Wet fog (20-30 micron VMD)
Mist (30-60 micron)
Fine Spray (above 60 micron)
Use Dry Fog droplets when you want droplets to diffuse widely. Use dry fog when wetting would lead to corrosion or a gas contact application such as odor control. The dry droplets have a greater surface to volume ration and diffuse easily with gas-like properties. They are more inclined to be carried by wind currents or prevailing wings.
The larger wet fog droplets are preferable for trying to settle dust or asbestos particles. Application for certain cleaning, mold control, or disinfection requires the surface to be wet. Fogging with a wet fog procedure would be superior over "mop and bucket" with uniform coverage, faster application, and speedy dry time.
You may need to experiment with the different droplet sizes for your particular application. For humidification purposes, you may need to balance the advantages of larger droplets with their higher flow rate (shorter run time) against the disadvantages of undesirable wetting, droplet fallout, and poor distribution. We recommend that you experiment with water (no chemical) in the location that you want to fog. If you need to use an oil-based fogger with an oil-based compound, substitute the water for kerosene.