Indoor Air

We need clean, fresh, moving air to stay healthy and comfortable.  Air remains clean when we control pollutant sources and we remove pollutants with ventilation or air cleaners.  What’s in your air?

Maybe! Most sources of air pollution have been with us for a long time, but some modern sources emit new pollutants. And tightly sealed buildings make problems worse by trapping pollutants indoors.

Air contaminants come from our bodies, buildings, heating, smoking, cooking, cleaning, and other activities — even from outdoor air and soil, and drinking water. Air pollution exists when there are high levels in the air, from sources with high emissions and/or from inadequate ventilation.


  • Reduced ventilation. We build tighter and seal up leaks with caulk, weatherstrip, gaskets, vapor barriers, etc.  We save conditioned (heated/cooled) air and money, but we trap pollutants indoors.
  • Back-drafting. Strong exhaust fans can suck combustion gases back down flues.

We can see or smell some pollutants.  We see smoke, or dust collecting. We see moisture condensed on windows, and the mold it causes on damp surfaces.  We smell many pollutants at high concentration levels, and some even at very low levels.  Many pollutants cause health problems at levels well below what we can see or smell.  They often irritate eyes, nose, throat, or lungs, causing respiratory problems (like allergies), headaches, nausea, skin rash, and many other symptoms (but we diagnose buildings, not people).


The effect of pollutants on our health is a product of both the concentration and the length of time we are exposed. We spend much of our time indoors.


Why test the air?  A survey can check for what might be in the air, but an air test can put a number on how much.  What to test for? The most common air tests are for mold, radon, carbon monoxide, and volatile organic compounds (VOCs).  How to test? with

  • Continuous monitors.
  • Active samplers with a vacuum pump to draw air through a sampler to collect the pollutants for later laboratory analysis.
  • Passive samplers that rely on air currents and diffusion to bring air to the sampler.
  • Surface samplers such as sticky tape to lift mold growth or settled dust.

We must control sources, pathways, and driving forces to minimize air pollution.

  • Seal sources of pollution to reduce the emissions and pathways.
  • Natural ventilation reduces concentrationsof all indoor air pollutants. Buildings always leak air, more on windy days. Even on calm days, the “stack effect” moves air by gravity — hot air rises and leaks out high, while cold air infiltrates below.  Simply opening windows often helps.
  • Mechanical ventilation with exhaust fans can remove moisture, odors, smoke, and solvents — best if used close to the sources.
  • Circulation avoids local buildup.
  • Keep combustion appliances (fuel-burning stoves, heaters, or furnaces) in good repair and properly vented to outdoors.
  • Control dust by cleaning and air filtration.


  • Water (H2O) vapor/moisture/humidity – Sources: Breathing, bathing, cooking, clothes dryers, plants, damp earth.  Effects: Moisture allows the growth of molds and bacteria, and increases the release of formaldehyde from materials.  Control: Stop leaks; dry. Ventilate, especially bathroom, kitchen, and bedroom. Circulate the indoor air.
  • Odors – Sources: Cooking, people, pets, mold, new materials.  Effects: Odors are sometimes just a nuisance, but might help find a hidden pollutant source.  Control: Ventilate kitchen and bathroom and any smelly or damp areas. Air out or wash new materials before using.
  • Particles, “particulate matter” – Sources: Smoke, soot, mold, dust, asbestos, lead paint, pesticides.  Effects: Lung and throat ailments. The smaller particles, inhaled deep into our lungs, can cause the most problems.  Control: Reduce the levels in the air with filters in furnace or portable air cleaners. Reduce mold growth by drying. Open doors and windows while vacuum cleaning.
  • Formaldehyde (HCHO) – Sources: Urea-formaldehyde (UF) resin in foam insulation (UFFI) or glues in interior particleboard (flooring, cabinets), paneling, treated fabrics, etc.  Effects: Upper respiratory (eyes, nose, throat) problems.  Control: Remove or seal sources. Reduce humidity. Wash new fabrics.
  • Chlorine (Cl2) bleach (hypochlorite). Sources: Chlorine-based cleansers. Effects: Lung irritation. Odor Control: Use diluted, with ventilation.
  • Ozone (O3) – Sources: High voltages from electronic air cleaners, older dry copy machines.  Effects: Throat and lung damage.  Odor/ effect somewhat like chlorine.   Control: Reduce voltages, clean off dust.
  • Radon (Rn) & radon decay products – Sources: Earth, rocks, well water.  Effects: Lung cancer.  Control: Vent soil gases.
  • Volatile organic compounds (VOCs) – Sources: Solvents in many products, “petroleum hydrocarbon distillates”, pesticides.  Effiects: various.  Control: Use solvents with good ventilation. Store fuels and solvents outside. Air out dry- cleaned clothes. Clean the air with activated carbon “charcoal” filters in an air cleaner.
GASES FROM COMBUSTION (burning fuels indoors, like in a heater or a gas stove)
  • Carbon monoxide (CO) – Effects: Drowsiness, headaches, death.
  • Carbon dioxide (CO2) – Sources: Breathing, burning.  Effects: Drowsiness.
  • Nitrogen oxides (NOx) = nitric oxide(NO) + nitrogen dioxide (NO2) – Effects: Upper respiratory irritation.

©Richard Knights, Blue Sky Inspections, Seattle,