Data quality
Sensor calibration — what makes monitoring data trustworthy
Every air quality measurement carries an assumption: that the instrument behind it is behaving as expected. Calibration is the discipline that keeps that assumption honest, sensor by sensor, deployment by deployment.
Why it matters
What calibration actually corrects
Offset and zero drift
Sensors shift their baseline over time. A zero check in clean reference gas or scrubbed air reveals offset before it contaminates the dataset.
Span and slope
A span check against a known concentration confirms the sensor's response across its working range, not just at zero.
Cross-sensitivity
Electrochemical and metal-oxide sensors respond to interfering gases. Calibration in representative conditions exposes how much this matters in the real environment.
Environmental dependence
Temperature, humidity and pressure influence many sensor types. Compensation is only as good as the calibration data behind it.
Methods
Factory, field and co-location
Factory calibration is performed under controlled conditions with traceable reference gases. It is the starting baseline — and the figure the manufacturer publishes. It does not, by itself, tell you how the sensor will behave on a school wall in February.
Field calibration brings the reference to the deployment. Portable calibration kits, span gas and zero air give a defensible check without removing the sensor. For network deployments, co-location against a reference instrument over weeks builds a correction model that captures the local environment.
Each method has a place. The choice depends on accuracy target, sensor accessibility, network size and the consequences of the decisions the data will inform.
Discipline
Calibration, verification, validation
| Activity | What it does | When it applies |
|---|---|---|
| Calibration | Adjusts the instrument against a traceable reference | Scheduled intervals, after relocation or after a major event |
| Verification | Confirms reading without adjustment | Routine checks between calibrations |
| Validation | Assesses fitness for purpose in the actual environment | After commissioning and periodically during the deployment |
| Data correction | Applies a model to historical data using paired references | Co-located networks and research deployments |
Limits
What calibration cannot fix
Sensor age
Electrochemical cells deplete. No calibration restores a depleted reagent — the cell needs replacement.
Poor placement
A sensor in a recirculating air pocket measures the air pocket, not the room. Calibration cannot rescue bad siting.
Inherent envelope
Low-cost sensors have a stated accuracy band. Calibration centres them within it; it does not narrow it.
Bad reference
A field calibration is only as good as the reference. Span gas certificates, transfer standards and reference instrument maintenance matter.
Records
Maintenance and traceability
A defensible monitoring programme keeps calibration certificates, field check logs, replacement dates and any correction factors applied. For regulatory contexts and dispute resolution, the audit trail is the data. Keep it from day one — retrofitting records into a year-old dataset is rarely satisfactory.
Suitable for
Who relies on calibrated monitoring data
Facilities and engineering teams
Decisions about ventilation, filtration and occupant exposure depend on data quality.
Schools and healthcare estates
Reporting to governing bodies and regulators needs traceable, validated measurements.
Consultants and environmental professionals
Investigations and certifications stand or fall on calibrated instruments and documented procedures.
FAQ
Calibration questions answered
Discuss an Air Quality Monitoring Project
From a single field check to a co-located network correction programme — calibration scoped to your data quality objectives.
Discuss sensor calibrationFurther reading
Sensors & monitors