Ionic air purifiers. They charge or magnetize the particles and then they cling to everything. Remove a picture from the wall - is the ghosting around the outside? Remove a metal decorative piece - if the particles are magnetized the ghosting will be the opposite - it will be in the same design as the item.
Are you sure it is not mold? That could be a health risk. If you heating with an oil fired furnace it might be cracked and allowing exhaust in your home. You might need to have this checked out proffessionally since the by product of this exhaust is carbon monoxide.
burning oil
To effectively remove ghosting stains on your ceiling, start by cleaning the affected area with a mixture of warm water and mild detergent. If the stains persist, try using a mixture of white vinegar and water or a commercial cleaner specifically designed for removing smoke and soot stains. Be sure to follow the instructions on the cleaner and test it on a small, inconspicuous area first. If the stains are still visible, you may need to repaint the ceiling to completely cover them.
To stop the black residue from a baseboard heater, the wall around and near the heater should be cleaned as there are dust particles attached to the wall. This is called ghosting which fine particles of soot attach to the wall that is cooler than the temperature.
Burning candles release soot and other particles into the air that can rise and accumulate on the ceiling over time. These particles can stick to the ceiling surface and create a dark, dirty layer. Using candles made from cleaner-burning materials can help reduce the amount of soot produced.
Incomplete combustion of carbon-containing compounds, such as hydrocarbons, can lead to the formation of black residue due to the production of elemental carbon (soot). This soot is responsible for the black color seen in the residue.
Soot is typically black in color.
soot
Soot will accumulate over time and may form more quickly if the gas contains impurities.
A black ceiling fan is likely to show the same amount of dust, unless the dust is dark in color. For instance, it could be mold spores or soot particles from candles. In this case a black fan will be less likely to show the particles.
Soot is a noun. It is the black residue left behind by burning some substances.
Black contrails in the sky are caused by the exhaust emissions from aircraft engines mixing with atmospheric conditions, such as temperature and humidity, resulting in the formation of soot particles that appear black in color.