What this category covers
Environmental monitoring measures the conditions around a site rather than inside a process: ambient air quality, dust and particulates, volatile compounds, noise, illumination, and the weather that moves all of them. The instrument is usually deployed where the exposure is, not where the operator is, which makes the physical installation part of the measurement in a way it rarely is elsewhere.
The output is generally a record over time rather than a reading at an instant. That shifts the important characteristics onto logging behaviour - interval, memory depth, power autonomy and how the data is retrieved - because a monitor that cannot survive the deployment or cannot give the data back is of no use however good its sensor is.
Where a measurement is made for compliance, the applicable method and the calibration interval are fixed by the permit, the standard or the contract rather than by preference, and the instrument has to be chosen to satisfy them. Establishing that requirement first avoids the common situation of an instrument that measures well but reports in a form the regulator does not accept.
Product types in environmental monitoring
| Product type | How it measures | Usually specified for |
| Air quality monitor | Electrochemical, infrared or optical sensing of the target gas in ambient air | Ambient and workplace air where a specific gas or a small group of gases is the reported parameter |
| Dust monitor | Optical scattering or gravimetric sampling of airborne particulate | Site boundary and workplace dust, and any location where a deposition or concentration limit applies |
| Particle counter | Individual particles are sized and counted optically as they pass a beam | Clean areas, filtration performance and indoor air work, where the size distribution matters as well as the count |
| VOC detector | Photoionisation of volatile compounds, with the lamp energy determining the response | Solvent handling, coating and printing areas, and any location where a total-volatile figure is the indicator |
| Noise meter | An integrating measurement of sound pressure, with weighting and time constants applied | Workplace noise assessment, boundary noise and any measurement reported as an averaged level |
| Light meter | A photodiode or filter-corrected sensor reads illuminance directly | Workplace lighting surveys and verification of a specified illumination level |
| Weather station | Combined wind, temperature, humidity, pressure and rainfall sensors on a mast | Site weather records, dispersion studies and any monitoring programme where conditions explain the readings |
| Environmental data logger | Accepts several sensor inputs and stores readings against a real-time clock | Long unattended deployments where the record has to survive a power or network interruption |
Temperature and humidity data loggers, radiation monitoring equipment, water quality monitoring equipment and complete monitoring systems are listed under this category as well.
How to choose a monitoring instrument
There is rarely a single correct instrument for a duty, but there is always a
shortlist that can be justified and a set of answers that eliminates the rest. These
are the questions that decide it.
- The parameter and the method, and specifically whether a regulatory, contractual or internal standard fixes how it has to be measured and reported.
- Whether the result is a spot reading or a record over time, which is the single decision that shapes the rest of the specification.
- The logging interval against the record length required, because together they set the memory depth and the power the unit needs.
- Placement and exposure, which for ambient measurement frequently matters more than the sensor, and cannot be corrected after the fact.
- The environment at the location: ingress protection, operating temperature range, whether the unit is exposed, and whether it has to be portable between points.
- How the data is retrieved and exported, and whether it has to reach a system or can be read from the instrument at the end of the deployment.
- The calibration route: whether a reference gas, an acoustic calibrator or a calibration service is available locally, and how often it is needed.
- Interference and cross-sensitivity, since an ambient measurement is rarely as clean as a bench one and the neighbouring substances matter.
- Whether the measurement is evidence. Where it is, the record has to be auditable and the calibration traceable to a reference.
Working through the selection in order
- State the parameter and whether a standard, permit or contract fixes the method and the reporting format.
- Decide whether a spot reading or a continuous record is required, and over what period.
- Set the logging interval from the phenomenon being recorded, and the record length from how often someone can visit the site.
- Work out the placement and the exposure, then choose the enclosure, the mounting and the power arrangement from that.
- Choose the sensing technology from the parameter and from what else is present in the air, using the comparison above.
- Confirm the calibration route and the interval, and how a calibration is carried out in the field.
- Decide the data route: local storage and collection, a direct connection, or transmission to a system.
- Confirm that the record produced will be accepted by whoever reads it, before the instrument is ordered.
Comparing the technologies
| Technology | Best suited to | Limits | Typical measurement |
| Electrochemical cell | Toxic gases and oxygen at low concentration in ambient air | The cell is consumed over time, cross-sensitivity between gases is common, and periodic calibration with a test gas is required | Gas concentration |
| Non-dispersive infrared | Carbon monoxide, carbon dioxide and combustible gas where sensor poisoning is a concern | Only responds to gases with an absorption band, and other absorbing species in the same band interfere | CO2, CO, combustible gas |
| Photoionisation | Volatile organic compounds at low concentration | The lamp energy determines which compounds respond, and the lamp and window are consumables with finite lives | Total volatile organic compounds |
| Optical scattering | Dust and particulate across a wide concentration span | Depends on stable flow and handles coincidence poorly at high counts; humidity changes the reading by changing particle size | Dust and particle concentration |
| Integrating sound measurement | Noise reported as an averaged level over a defined period | The result depends on weighting, time constant and microphone placement, and the instrument needs calibration against an acoustic source | Noise level |
| Direct physical sensing | Illumination, wind, rainfall and the general weather record | Placement and exposure dominate the reading, and a badly sited sensor cannot be corrected afterwards in software | Light, wind, rainfall, climate |
Parameters to confirm before ordering
What is left after the technology is chosen is a list of values that only the
installation can supply. These are the ones that change the model, the price or the
lead time:
- The parameters to be monitored, and any method or standard the result has to satisfy.
- The measurement location and the conditions there, including exposure, temperature range and available power.
- Whether the requirement is portable, wall mounted or permanently installed outdoors.
- The logging interval and the record length needed, and how often the site can be visited.
- The alarm or notification requirement, if any, and where it has to go.
- The gases or substances expected alongside the target, since interference affects the choice of sensor.
- The calibration and reference materials available locally, and the interval the method requires.
- How the data is retrieved and in what format, including any system it has to feed.
- Whether the record forms part of a compliance obligation, and what form it has to take.
- Quantity, and whether the deployment covers one point or a network of locations.
Figures are quoted, not assumed
Specifications vary by model and application, so no performance figure is stated on
this page. Where a parameter has not been documented for a particular model, the
product page says so rather than filling the gap with a plausible number. Send the
values above and we will return the ones the selected model actually holds.
Where these instruments are used
