Chasing a mystery odor is one of the most fun things I do, because it’s just my nose and my knowledge of buildings and typical sources.  (See the following page on finding a source.)

Of course if you recognize the odor, that might suggest a source right away.  (Like my neighbor Nancy, where the odor said dead rodent, but the task was finding out where.)

Odor Identity

  • Most odors are volatile organic compounds (VOCs), as are most of the gases we breathe.  Some are aldehydes, like “mold VOCs”.  Or amines, like putrescine or cadaverine.  Or terpenes like limonene and pinene (in turpentine, or cleaning products).  Or sulfur compounds, like methyl mercaptan (the odorant in natural gas).  Or phenols (cleaning products) or alcohols (paint glycols).
  • Other odors include hydrogen sulfide (H2S like rotten eggs), chlorine, ammonia.
  • Most problems come from low levels of very stinky compounds (with very low odor thresholds).

Odor Testing

  • Detect the odor:  the human nose and our sense of smell  is the fastest, most sensitive, smartest tool we have.
  • Describe the odor:  Does the problem area smell unusual? or like new carpet, paint, gasoline, solvent, smoke, burnt, food, stale, sour, rotten, damp, earthy, musty, moldy, urine, bad, sewage, dead, stink, or stench?  Avoid the word “chemical”, because of course everything in our physical world is a chemical.
  • Find the source of the odor.
  • Measure high levels of VOCs from a surface using thermal conductivity with a continuous direct reading combustible gas detector (Tif #8800A) that beeps faster nearer the source.  Or use a photoionization detector (PID) that reads in parts per million parts of air (ppm).
  • Identify individual VOCs:  For lab analysis of air samples, use GC/MS (gas chromatography with mass spectrometry), searching for VOCs with low odor thresholds such as terpenes, phenols, aldehydes, and alcohols.  (This is slow, expensive, and rarely useful.)

Odor Sources

  • Understand odors to help find the source.
  • A source size can be:
    • a point source (like a wall penetration), often strong and obvious when found, or
    • an area source (like wall or ceiling paint, or a wood finish), often weak and difficult to find, but the large area can still fill a room.
    • a fleeting, peripatetic source (difficult to find).
  • A source strength may be decaying:
    • continual source will not go away until stopped, or
    • a decreasing source is going away, then
    • residual source is much less, and slowly going away, but persistent (like creosote in wood, or fuel oil on a concrete floor).
  • A source type may be:
    • primary source that causes a problem, or
    • secondary source that absorbed an odor from a primary source, and became only a residual source after the primary source was removed.
  • Activities:  cooking, stoves, people, pets.
  • Building materials, either new or damp/moldy.
  • Heated source (heater, light fixture, electronics) that might emit only when hot.
  • Hidden source, like inside wall/floor cavities (may depend on wind direction), or behind cabinets.

Odor Effects

  • Odors are sometimes just a nuisance (like a very low level of something very stinky), but they might help find a hidden pollutant source (like mold inside a wall).

Odor Source Control

  • Remove suspect materials to see if the odor goes away.
  • Ventilate kitchen and bathroom and any smelly or damp areas.
  • Air out or wash new materials before using.
  • Pour water down a stinky floor drain every few months to keep the trap full and avoid sewer gases from entering.  And pour down a half-cup of mineral or cooking oil to slow water loss by evaporation.
  • Open a wall to expose and remove a source hidden inside an exterior wall cavity; or seal penetrations and positively pressurize the building to stop an odor leaking in.
  • Fumigate the unoccupied room or building with ozone for a day or more, then ventilate an hour or more.

Air Cleaning

  • Add a bed of granular activated charcoal (GAC) to your furnace or air handler cold air return (after the filter) to adsorb odors and other gases.
  • Use portable air cleaners with granular activated charcoal in rooms with the most odor.  (Call Sarah or Jim at AAA Aircare Systems 206-367-8600 to choose one or more.)

One of my clients called his intermittent odor “peripatetic” (walking about) until we found the source just sitting down hiding under a desk.