Measuring the ozone level in a room with people
Information provided by EcoSensors.
Ozone concentrations can vary greatly in various places and the concentrations are often higher in unexpected places.
The key points to consider are:
Ozone is much heavier than air and tends to sink to lower levels.
Ozone has a low vapor pressure and therefore does not try to fill the room evenly. It tends to stay where it is.
Ozone tends to adhere to rough surfaces such as fabric and decomposes (is converted back to oxygen) as it passes through restricted and obstructed passageways.
Ozone becomes oxygen again with a "half-life" (time to reach half of its original concentration) typically 10-30 minutes.
The instrumentation can confuse ozone with other oxidizing gases such as chlorine compounds, acid fumes, and nitrogen oxides (NOx). Strong "reducing" gases, such as alcohol and solvent vapors, can reduce the apparent concentration of ozone.
Ozone has a sweet odor, but the odor threshold varies greatly depending on the person and the environmental conditions. Therefore, "odor" is not a reliable test for the presence or concentration of ozone.
The important measure is: What is the ozone concentration at the respiration level where the occupants of the room will be?
For ozone introduced through ducted air systems with good ambient air circulation, the alternate measurement point is near the entrance to the return air duct.