Black dust around your air vents is most often soot that can come from burning candles, using wood burning fireplaces or stoves or other things that can produce soot.
In some cases the black stuff around your air vents could be black mold.
Air vents are an ideal environment for many varieties of mold.
The air vents are dark, isolated, and have plenty of dust, which comprises organic matter for mold to metabolize.
Once condensation or moisture starts to accumulate, you've got the perfect conditions for mold to thrive.
Soot tends to cling to cold, damp spots on surfaces, forming dark stains, patches, and streaks on walls, ceilings, cabinets, and refrigerators.
The soot particles can originate from candles, furnaces, tobacco smoke, and even dust from the chimney, a vent, or even outside.
The black dust which is patchy and not so easy to wipe off can be a sign of black mold growing inside your air vents.
Mold formation can indicate problems with the air conditioning system.
One of the most effective ways to remove mold from your air ducts is by using a homemade solution of baking soda, detergent, and water.
This mix is efficient and safe for your health and the environment.
Common sources of black stuff around your air vents include burning paraffin wax candles, vegetable oil-based candles, or petroleum jelly candles, which emit black soot that can circulate through your HVAC system.
Using wood-burning fireplaces or stoves can also introduce black soot into your vents.