Measuring Ozone in Air

Many applications require measurement and control of ozone of very low concentrations under 300 ppb (parts per billion). At these low concentrations, one needs to consider the following sampling issues with measuring ozone.

Ozone Characteristics

Ozone is Highly Reactive

1. Ozone is highly reactive. Ozone will react readily with organic materials and surfaces such as walls, flooring, ceiling material, plastic test chambers and people. The greater the accuracy of the ozone monitor, the greater the variations will become apparent. If you are testing the accuracy of ozone monitors in test chambers, ensure the devices inside the chamber are clean and do not readily react with ozone. Such materials that work well are fluoropolymers and glass.
2. Ozone will react with dust and oils. Ensure that all surfaces are clean and that any solvents used to clean such surfaces have completely dried. Even slight solvent residuals will have a dramatic effect on the sensor and residual ozone level in the chamber.
3. Ozone concentration gradients are common in rooms and are greatly influence by air movement and eddy currents. This effect will be more pronounced at concentrations less than 100 PPB.

Monitor Design and Use

• Aeroqual’s ozone monitors are designed with "active sampling" to maximize air sampling at the sensor (to minimize ozone losses). Most expensive, analytical instruments also employ active sampling (e.g. UV photometry).
• Products without "active sampling" (electrochemical and conventional HMOS products) will normally under-read ozone concentrations below 200 parts per billion and struggle with sensitivity and accuracy, particularly in low air flow.
• "Active sampling" requires air to be blown or pumped to the sensor under precise flow conditions. Aeroqual fan based monitors are designed to be held at right angles to any direct stream being measured. Avoid forcing pressurized air into active sampling monitors.
• Air inlets are manufactured from cleaned stainless steel mesh and fluoropolymer materials to minimize ozone loss. Do not use sampling tubing:
  • that alters flow characteristics,
  • that reacts with ozone,
  • longer then 1 foot or 30 cm on pumped based monitors without PTFE filters, e.g. centralized monitoring systems.