Are PID sensors better than MOX for VOC monitoring?

Photoionisation detectors (PID) respond to a wider range of compounds with better stability, which makes them suitable for industrial and workplace monitoring. MOX semiconductor sensors are cheaper and useful for indicative indoor TVOC trends but are more affected by humidity and temperature.

Can a TVOC sensor identify the source of an odour?

Not directly. TVOC will rise during a release event but cannot identify which compound is responsible. Source attribution typically combines spatial sensor data, occupancy correlation and sorbent-tube sampling with laboratory analysis.

VOC monitoring

VOC monitoring — TVOC trends and the limits of broad readings

Volatile organic compounds emerge from materials, cleaning products, processes and occupants. Continuous TVOC monitoring identifies when something has changed; targeted sampling identifies what.

Laboratory glassware representing VOC analysis

AirQualityTech.uk · Editorial

Sources

Where indoor VOCs come from

VOC profiles vary widely between building types. Continuous monitoring is most useful when paired with knowledge of likely source classes.

Materials & furnishings

New paints, adhesives, sealants, carpets and engineered wood emit VOCs as they cure.

Cleaning & maintenance

Solvent-based cleaners and disinfectants release short-duration TVOC spikes.

Processes

Workshops, kitchens, laboratories and printing rooms have characteristic compound profiles.

Occupants

Personal care products, scented items and bioeffluents contribute a continuous background.

Method

How VOC sensors work — and what they cannot do

Indoor monitors typically use metal-oxide semiconductor (MOX) sensors, which respond to a broad mix of reducing gases. Calibrated to an isobutylene equivalent, they output a single TVOC value useful for trending and event detection.

Industrial and occupational applications usually call for photoionisation detectors. PID sensors offer a wider response and better stability, with results expressed against a reference compound. They still cannot identify individual species.

When identification matters — odour complaints, exposure assessment, BREEAM evidence — the workflow combines continuous TVOC monitoring with sorbent-tube sampling. Tubes are sent to an accredited laboratory and analysed by thermal desorption and gas chromatography to quantify specific compounds.

Comparison

TVOC sensor types at a glance

Sensor	Strengths	Limitations	Typical use
MOX (metal-oxide)	Low cost, compact, suitable for continuous indoor monitoring	Sensitive to humidity and temperature, indicative only	Office / classroom IAQ
PID (photoionisation)	Wider VOC response, better stability and selectivity	Higher cost, lamp servicing	Workplace and industrial
Sorbent tube + GC-MS	Identifies and quantifies specific compounds	Sampling event only, laboratory turnaround	Exposure assessment, source investigation

Investigation

From a TVOC spike to a confirmed source

Detect the event

Continuous TVOC sensors flag a sustained rise above baseline.

Correlate

Cross-reference timing with occupancy, cleaning schedules and processes.

Spatially confirm

Compare adjacent zones to find the zone of origin.

Quantify

Where exposure matters, take sorbent-tube samples for laboratory analysis.

FAQ

VOC monitoring questions

TVOC (total volatile organic compounds) is a single aggregated reading used for trending. Specific compounds — benzene, toluene, xylenes, formaldehyde and others — are identified and quantified through targeted sampling and laboratory analysis.

Discuss an Air Quality Monitoring Project

Continuous VOC monitoring, source investigation and targeted compound analysis for UK commercial buildings.

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