Sensors - VOC

Aeroqual offers three different types of sensor technology for the measurement of volatile organic compounds (VOCs), including non-methane hydrocarbon (NMHC).

These sensors respond to a broad range of VOCs although they each display a unique sensitivity to certain VOCs or classes of hydrocarbon.

• The three sensors are all sensitive towards aromatic hydrocarbons.
• PID type sensors use a 10.6 eV UV lamp that has a run time of up to 5000 lit hours. The operating life of the Sensor Head is up to 5 years with lamp replacement.
  • With our Hot Swap program, this is no longer a concern. Talk with your Aeroqual Representative to learn more!
• This lamp breaks down the VOCs into positive and negative ions. The detector measures the current of the ionized gas. The measured current is proportional to the concentration of VOCs present in the sample.
• None of the sensors respond to methane.
• The NMHC sensor and VOC sensor show unique sensitivity towards certain organic compounds.

All VOC sensors are calibrated at the Aeroqual factory using isobutylene. This means in the presence of 1 ppm isobutylene all three sensors will report 1 ppm.

The isobutylene conversion factor from ppm to mg/m3: 1 ppm = 2.29 mg/m3

However in the presence of other volatile organic compounds, the response will be very different for each sensor type. The PID sensor is an industry standard and has correction factors for a range of different gases (see PID sensor response correction factors below).

Note: If the GSS VOC or GSS NMHC sensor is being used to measure another organic compound, we advise you calibrate the VOC sensor towards that compound using a gas standard comprised of that compound.

The differences and similarities in selectivity of the different compounds should be considered when choosing a sensor for a specific application.

Other related compounds can be measured using Aeroqual’s specific sensors.

Note: If the atmosphere being measured contains a mixture of hydrocarbons (this is likely when measuring outdoor ambient air), consider measurement to be quantitative only.

The PID sensor response to a variety of gases is given in the table below. The response factor (RF) provides a sensitivity measure relative to isobutylene (RF=1). The PID sensor is more sensitive to compounds with lower RF values. Compounds not listed may also be detected by PID. For more information contact Technical Support.

VOC (PID) sensor specifications

Response factors

The default sensor concentration reading is in units of ppm of Isobutylene. You can convert this into ppm of another gas by multiplying the reading by an identified response factor.

Correction factors for a range of different gases for the PID sensor can be found on the Ion Science website. Search for the target gas, view the product details, then find the value for Gas Response Factor, 10.6 eV in the specifications section.

PID sensor response factor example

The PID sensor head is calibrated against Isobutylene and is being used to measure the concentration of heptane.

The reading in ppm of Isobutylene is 10ppm.
Therefore the concentration of heptane is 10ppm x 2.2 = 22ppm.

The PID sensor can also be used to qualitatively indicate the total VOC level. The units of measurement are ppm Isobutylene equivalent.

More information can be found here regarding the GSE Sensors and their cross-sensitivities: GSE Sensor Responsiveness

The Aeroqual GSS sensor response to a selection of gases is given in the table below. The response factor (RF) provides a sensitivity measure relative to isobutylene (RF=1). The GSS sensor is more sensitive to compounds with lower RF values. Compounds not listed may also be detected by GSS. For more information contact Technical Support.

VOC (GSS) sensor specifications

Response factors

*A smaller RF means the GSS is more sensitive to the compound.