MiniPID 2 HS Sensor Deployment Guidelines

Introduction
Photoionisation detection (PID) sensors enable measurements of a wide range of organic volatiles in air at concentrations ranging from parts per billion to low percentages. The full range of the MiniPID 2 HS sensor is only 3000 ppb (3 ppm) isobutylene.  Isobutylene is universally used as a PID calibration gas.  In this document unspecified PID responses in ppb refer to an ppb isobutylene equivalent response calculated by frequent calibration of sensors with 2 ppm isobutylene. 

PID responses greater than ~3000 ppb cause a saturated HS MiniPID signal.  VOC readings >3000 ppb can be expected in some commonly encountered  environments, for example:

• Near heavy traffic, exacerbated by weather conditions or roadway architecture (eg urban canyons),  and at sites of unsealed refuelling  and fuel spillage (eg station forecourts).

• In industrial facilities where volatiles are routinely used in coatings and paint  preparations, or as a solvent.

• In clean rooms and heavily conditioned  or refrigerated environments where volatiles accumulate  due to low air turnover.

• In unventillated rooms and enclosed spaces where VOC’s have been allowed to accumulate.

• In domestic environments on occasion of heavy release of volatiles, such as from paints and varnishes, use of certain cleaning fluids or during cooking. 

By contrast, clean rural air delivers a PID response of less than 100 ppb.  In reasonably ventillated interior spaces at 20 to 25 oC (68 to 77 o F), 200 to 400 ppb is typical. However, these ambient levels increase significantly in the absence of ventillation and at higher temperatures

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