Not all indoor air quality data is equal: Why monitoring accuracy, standards and certification matter 

As indoor air quality monitoring becomes increasingly important in creating healthier buildings, greater attention is being paid to the accuracy, reliability and consistency of the data these devices provide. 

Indoor air quality (IAQ) monitoring has become an increasingly important part of building management. From offices and schools to healthcare facilities and commercial developments, organisations are investing in monitoring technology to understand the environments in which people spend time. However not all indoor air quality monitors measure air pollution in the same way, to the same degree of accuracy, or with the same level of reliability.

Two monitors installed side by side can produce markedly different readings. Devices marketed as measuring the same pollutants may use entirely different sensing technologies, calibration methods and data processing algorithms. Even the way measurements are reported can vary between manufacturers. For building owners, facilities managers and organisations making decisions about occupant wellbeing, this presents a fundamental challenge with regards to what readings can they trust. A new international initiative is bringing this issue into sharper focus.

A global framework puts measurement reliability under the spotlight

The International WELL Building Institute (IWBI) has established the Global Commission on Healthy Indoor Air, bringing together expertise to accelerate improvements in indoor air quality. Its Global Framework for Action outlines a roadmap built around five interconnected priorities: awareness, policy, standards, market adoption and measurement.

Of particular relevance to the air quality monitoring industry is the recognition that gaps in accepted standards for sensor accuracy and interoperability are holding back progress. The framework calls for greater attention to calibration, validation, data comparability and the ability of monitoring technologies to communicate with building systems. As indoor air quality monitoring becomes more widespread, simply increasing the number of sensors installed in buildings will not necessarily produce better outcomes. The quality of the information those sensors provide matters just as much as the quantity. Without confidence in the measurements, organisations risk making decisions based on incomplete, inconsistent or misleading information.

Why do indoor air quality monitors produce different readings?

It is reasonable to assume that two devices measuring the same pollutant, in the same location, should produce approximately the same result. In practice, this is not always the case. There are several reasons why readings can differ and understanding them is essential when evaluating monitoring equipment.

1. Different sensing technologies produce different results

Indoor air quality monitors use different types of sensors to measure pollutants, and the technology used can affect the accuracy and reliability of the results.

Carbon dioxide (CO₂) monitoring is one example. Some devices use non-dispersive infrared (NDIR) sensors to measure CO₂ concentrations directly. Others, particularly lower-cost monitors, do not measure CO₂ at all. Instead, they estimate CO₂ levels using readings from volatile organic compound (VOC) sensors. This estimated value, known as eCO₂, is not the same as a direct CO₂ measurement. VOCs can be released by cleaning products, furniture, building materials and other sources, even when CO₂ levels remain unchanged. As a result, a monitor that estimates CO₂ from VOC readings may indicate a rise in CO₂ when the actual concentration has not increased. This makes eCO₂ less reliable for assessing ventilation and indoor air quality.

Similar limitations apply to particulate matter (PM) monitoring. Most compact air quality monitors use optical sensors to detect airborne particles and estimate concentrations of PM2.5 and PM10. However, these sensors do not directly measure the mass of particles in the air. Instead, they use the way particles scatter light to calculate an estimated concentration. The accuracy of these estimates can be affected by several factors, including particle size, composition, humidity and the calculations used by the device.

This explains why two air quality monitors placed in the same room may display different PM2.5 or PM10 readings. Neither device is necessarily faulty; they may simply use different sensors or methods to calculate pollutant concentrations.

The key point is that not all air quality monitors measure pollutants in the same way. Understanding whether a device provides a direct measurement or an estimate, and how its sensors work, is essential when interpreting readings and comparing monitoring equipment.

2. Calibration can make a substantial difference

Every sensor has measurement characteristics that influence its accuracy. Calibration establishes how a sensor's response relates to a known reference. Without appropriate calibration, even a technically capable sensor may produce inaccurate readings. However, calibration practices vary across the market.

Some devices undergo factory calibration against defined reference conditions. Others rely heavily on automatic correction algorithms or receive limited calibration before deployment. Certain sensors also require periodic recalibration or replacement to maintain their performance.

For example, some CO₂ sensors use automatic baseline correction algorithms that assume the sensor will periodically be exposed to air with a known background CO₂ concentration. This approach can be effective in buildings where CO₂ levels regularly return to the expected baseline but may be less reliable in continuously occupied or poorly ventilated environments where those conditions are not met. Depending on the sensor technology and calibration algorithm, this can introduce measurement errors or affect long-term accuracy.

Calibration is therefore not simply a manufacturing detail. It is a fundamental part of ensuring that data remains dependable throughout a device's operational life. Importantly, a calibration certificate alone does not guarantee permanent accuracy. The calibration method, reference equipment, measurement uncertainty and ongoing maintenance requirements all matter.

3. Environmental conditions influence sensor performance

Air quality sensors operate in complex environments. Temperature, relative humidity, airflow and the presence of other airborne substances can all influence measurement performance. For instance, high humidity can affect optical particle measurements because hygroscopic particles absorb moisture and increase in size. Certain gas sensors may also respond to substances other than the pollutant they are intended to detect, a phenomenon known as cross-sensitivity.

These effects are particularly relevant in buildings where environmental conditions change throughout the day. A monitor that performs well under controlled laboratory conditions may behave differently in a busy office, industrial facility or school. This is why sensor validation should consider realistic operating conditions rather than relying solely on controlled specifications.

4. Sensor placement and sampling methods matter

Even two accurate monitors can produce different readings if they are positioned differently. Air pollution is not distributed uniformly throughout a building. Concentrations can vary with proximity to ventilation outlets, windows, doors, occupants, printers, cleaning activities and other pollution sources.

A monitor mounted near a window will likely report different concentrations from one positioned in a poorly ventilated corner. Sampling frequency, response time, airflow through the instrument and data averaging periods can also affect the results. For example, one device might report a near-instantaneous reading while another displays a rolling average over several minutes. Neither reading is necessarily incorrect, but they are not directly comparable without understanding how the data has been collected and processed.

5. Manufacturers do not always report data in comparable ways

One of the less visible causes of disparity is how manufacturers process and present their measurements. Devices may use different filtering algorithms, correction factors, averaging intervals and reporting conventions. Some display raw or minimally processed measurements, while others apply substantial proprietary processing before presenting a final value.

VOC measurements for example, can be difficult to compare. One monitor might report a total VOC estimate in parts per billion, another in micrograms per cubic metre, and another as a relative air quality index. These values cannot necessarily be converted or compared directly because they may represent different measurement principles and assumptions.

Without clear documentation, users may believe they are comparing equivalent measurements when they are not.

The central issue is not simply whether a monitor produces a number. It is whether that number is meaningful, traceable and suitable for the decision being made.

Why unreliable data creates a bigger problem for buildings

The consequences of inconsistent monitoring extend beyond technical disagreements between manufacturers. Indoor air quality data increasingly informs ventilation strategies, building performance assessments, occupant communications and investment decisions. If the underlying information is unreliable, the decisions based on it may also be compromised.

A monitor that consistently under-reports pollutant concentrations could create a false sense of reassurance. Conversely, a device that over-reports concentrations might prompt unnecessary interventions or lead building managers to question otherwise effective ventilation systems.

For organisations managing multiple properties, the challenge becomes even more significant. If different buildings use monitors with inconsistent accuracy, calibration or reporting methods, comparing performance across an estate becomes difficult. A building appearing to perform better than another may simply be using different monitoring technology. This undermines the value of benchmarking and makes it harder to establish meaningful performance improvements. As organisations increasingly rely on environmental data to demonstrate progress against healthy building objectives, confidence in measurement quality is essential.

The role of standards: establishing a common basis for measurement

The IWBI Global Commission's focus on standards is particularly relevant because the indoor air quality monitoring market includes a wide range of products with very different performance characteristics. Standards provide a way to establish common expectations. Rather than relying exclusively on manufacturers' claims, buyers and specifiers can assess equipment against recognised performance criteria.

These may address factors such as:

• Measurement accuracy and uncertainty.
• Repeatability and reproducibility.
• Sensor response time and detection limits.
• Long-term stability and measurement drift.
• Performance under different environmental conditions.
• Cross-sensitivity to other pollutants.
• Calibration and validation procedures.
• Data reporting and interoperability.

There is no single universal standard that comprehensively certifies every indoor air quality monitor, every pollutant and every application. Different standards and assessment schemes address different aspects of measurement performance. This makes it essential to understand exactly what a particular standard or certification covers.

Understanding the standards and certifications that matter

Several existing frameworks already provide important foundations for more reliable indoor air quality monitoring.

MCERTS: independent assessment of monitoring performance

In the UK, the Environment Agency's Monitoring Certification Scheme, known as MCERTS, provides a framework for assessing environmental monitoring equipment against defined performance requirements. Where an appropriate MCERTS certification applies, it provides independent evidence that equipment has been tested and assessed against specified performance criteria.

This can provide greater assurance than relying solely on a manufacturer's unverified accuracy claims. However, MCERTS primarily covers defined environmental monitoring applications, including ambient air quality, and is not a universal certification scheme for all indoor air quality monitors or pollutants. Buyers should therefore check exactly which instrument or component has been certified, which performance standards apply and what the certification covers.

ISO 16000: establishing consistency in indoor air quality measurement

The ISO 16000 series provides international standards specifically concerned with the measurement and assessment of indoor air quality. It covers a range of monitoring considerations, including sampling strategies, measurement procedures and methods for assessing individual pollutants such as carbon dioxide, volatile organic compounds and airborne particles.

For example, ISO 16000-1 provides guidance on planning indoor air monitoring, including where, when and how frequently measurements should be taken, while ISO 16000-26 addresses sampling strategies specifically for carbon dioxide. Other parts of the series establish methods for measuring particular pollutants and testing certain detection technologies.

These standards are important because differences in monitoring locations, sampling methods and measurement procedures can contribute to inconsistencies in reported air quality data. Establishing common approaches can therefore help improve the reliability and comparability of measurements.

ISO 16000 is not a universal certification standard for indoor air quality monitoring devices. While it provides a framework for consistent measurement practices, it does not guarantee that different monitors will deliver the same level of accuracy or performance. Independent validation, appropriate calibration and transparent technical specifications remain essential when assessing the reliability of monitoring equipment.

WELL and RESET: encouraging better monitoring practices

Healthy building certification programmes are also influencing how indoor air quality is measured, monitored and managed. The WELL Building Standard, developed by the International WELL Building Institute (IWBI), includes requirements relating to indoor air quality, ventilation and building performance. It encourages organisations to assess indoor environmental conditions and demonstrate that their buildings meet defined health and wellbeing criteria, using appropriate testing and verification methods.

RESET Air is an international standard and certification programme with particular emphasis on continuous indoor air quality monitoring, establishing requirements for sensor performance, monitoring locations, data collection and reporting. Its approach helps organisations move beyond occasional air quality assessments towards ongoing measurement, providing greater visibility of changing indoor conditions and supporting more informed building management decisions.

Both programmes are helping to establish clearer expectations for the quality, consistency and accessibility of indoor air quality data. They also reinforce the importance of selecting monitoring equipment that is appropriate for its intended application and capable of producing reliable, meaningful measurements over time.

However, building certification and device certification are not the same thing. A building achieving a particular certification does not necessarily mean that every installed monitor has been independently tested or certified for every pollutant it measures. Equally, a monitor being suitable for use in a WELL or RESET project does not automatically demonstrate independent certification of its measurement accuracy. Understanding these distinctions is important for building owners and specifiers when assessing monitoring equipment and the reliability of the data it provides.

Regulation: will monitoring requirements become more consistent?

Standards and voluntary certification can improve confidence, but their impact depends on adoption. This raises a wider question: should there be more consistent regulatory expectations for indoor air quality monitoring?

Across the UK and internationally, building regulations, workplace health requirements and environmental policies already influence aspects of ventilation and indoor environmental quality.  However, these requirements should not be confused with a universal legal obligation to install certified continuous indoor air quality monitors. The regulatory position remains fragmented, and monitoring obligations depend on the building, jurisdiction and application.

A more consistent approach could help by establishing clearer expectations for monitoring performance, calibration, data quality and reporting. It could also make procurement more transparent, giving building owners greater confidence that equipment has been assessed against relevant technical criteria.

The objective should not be regulation for its own sake. It should be to ensure that measurements used to inform important building management decisions are sufficiently reliable for their intended purpose.

Interoperability: accurate data must also be usable

Measurement accuracy is only part of the challenge. For indoor air quality monitoring to deliver its full value, information must be accessible and capable of being integrated into wider building systems. This is another area highlighted by the Global Commission's framework.

Many buildings contain a mixture of monitoring equipment, building management systems, ventilation controls and software platforms. If those systems cannot communicate effectively, environmental information can become isolated. Proprietary interfaces, inconsistent data formats and limited access to historical measurements can make integration unnecessarily difficult.

Open communication technologies and well-documented interfaces can help address these barriers. For example, LoRaWAN enables low-power wireless devices to transmit measurements across buildings and wider estates. When supported by appropriate integration infrastructure, this data can be incorporated into building management and analytics platforms.

However, connectivity alone does not guarantee interoperability. Systems must also agree on data definitions, units, timestamps, measurement locations and quality indicators. A genuinely interoperable monitoring strategy should enable organisations to access, interpret, compare and retain their environmental data without unnecessary dependence on a single software platform. This becomes particularly important when managing large property portfolios or combining information from multiple manufacturers.

What needs to change?

Improving trust in indoor air quality data requires action from manufacturers, standards bodies, regulators, specifiers and building operators. Five areas deserve particular attention.

1. Greater transparency from manufacturers

Manufacturers should clearly disclose the sensing technologies used, the parameters measured, the conditions under which accuracy claims apply, and the calibration and maintenance requirements. Where measurements are estimated rather than directly measured, this should be made explicit.

2. More independent testing and validation

Independent assessment against recognised performance criteria can help establish whether monitoring equipment performs as claimed. Certification should be encouraged where appropriate schemes exist, with clear information about what has actually been assessed.

3. Consistent measurement and reporting practices

Standardised units, averaging periods, calibration procedures and reporting conventions would make data easier to interpret and compare. This would be particularly valuable for organisations monitoring multiple buildings or using equipment from different suppliers.

4. Better integration with building systems

Monitoring data should be accessible through documented interfaces and capable of supporting wider building management applications. Open communication approaches, consistent data structures and transparent integration requirements can reduce unnecessary barriers.

5. Stronger procurement and specification requirements

Building owners and consultants can influence the market by demanding clearer evidence of performance. Rather than selecting equipment solely on purchase price or the number of parameters advertised, specifications should consider accuracy, calibration, validation, certification, long-term stability and data accessibility.

Together, these measures would encourage a more consistent approach to indoor air quality monitoring.

Synetica's approach: precision, transparency and usable data

At Synetica, we believe that effective indoor air quality management begins with confidence in the measurements. Our enLink range of indoor air quality monitors, designed and manufactured in the UK, places an emphasis on measurement performance, practical deployment and accessible environmental data.

The range incorporates established sensing technologies, calibrated sensor options and detailed technical specifications to help customers understand what their equipment measures and how it performs. Selected products incorporate MCERTS-certified particulate matter sensing technology, while monitoring solutions support applications associated with WELL and RESET building requirements.

Using LoRaWAN connectivity, enLink devices can transmit environmental measurements for integration into wider monitoring and building management systems. Data ownership and accessibility are also important considerations, with the hardware designed to support subscription-free operation. This allows organisations to access and use their environmental information without being tied to a mandatory proprietary monitoring subscription.

For us, reliable monitoring is not simply about generating readings. It is about providing measurements that building owners, consultants and facilities teams can understand, interrogate and use with confidence.

The future of healthy buildings depends on trustworthy data

The IWBI Global Commission on Healthy Indoor Air has brought renewed attention to an issue that the monitoring industry must address. Improving indoor air quality is not simply a matter of installing more devices. It requires reliable measurement, appropriate calibration, transparent performance information, meaningful standards and the ability to compare data across different buildings and systems.

As demand for healthier indoor environments grows, these requirements will become increasingly important. Manufacturers have a responsibility to demonstrate how their equipment performs. Standards bodies and certification organisations have an important role in establishing common expectations. Building owners and specifiers must also ask more demanding questions about the technology they purchase.

Ultimately, the value of indoor air quality monitoring is determined not by how much data is collected, but by how much confidence we can place in it. If we want better buildings, we need better measurements. And that starts with recognising that not all indoor air quality data is created equal.

Further reading

• IWBI – Global Commission on Healthy Indoor Air
• IWBI – Global Framework for Action (PDF)