Support

Deep dive: VOCs & Particulates

All you need to know about AirSuite's Volatile Organic Compound (VOC) and Particulate Matter (PM) sensors.

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If you want to learn more about how your VOC and PM sensors work under the hood, you’re in the right place. Read on to discover:

• The dangers of high exposure to VOCs and PM;
• How the sensors operate;
• How they calibrate, and;
• Technicalities to keep in mind.

Firstly, which materials or processes are responsible for VOC exposure?

Cleaning products, chemicals, craft and building materials, flames and combustion, vehicle fumes, and thousands of other processes and sources emit volatile organic compounds (VOCs).

Even installing new furniture or carpet from factories that undergo industrial processes, can expose you to VOCs.

Why’s it important to monitor VOCs?

Because they impact a building’s indoor air quality. At high levels, they can be very harmful. The health impact can range from mild airway irritation to serious respiratory issues and cancer.

What do AirSuite’s VOC sensors measure?

AirSuite sensors measure total VOCs (tVOCs) - that’s the total concentration of VOCs present in the air, measured in parts per billion.

What affects the accuracy of VOC sensor measurements?

VOC sensors are extremely sensitive, meaning that if you expose them to high VOC levels, you’ll see the readings spike within seconds. Try it out by putting some hand sanitiser or perfume next to the sensor, and checking the readings via the AirSuite mobile app.

However, the sensor calibrates itself based on its past measurements on a daily basis, so if it is constantly exposed to high levels of VOCs it may appear not to detect them. For best results, keep the space well-ventilated so that the sensor is frequently exposed to fresh air.

It is unlikely that you’ll notice when the VOC sensor applies calibration adjustments, because of how often it self-calibrates. This is different from, for example, CO₂ sensors, which can have a sudden spike during calibration.

The other factor affecting accuracy is the start-up time: when you first turn on your sensor, it needs to warm up a heating element before it can provide accurate readings.

How long does it take for the VOC sensor to warm up?

The amount of warm-up time your sensor needs depends on the power mode it is operating in. In AirSuite devices, we apply a different power mode depending on whether the device connects to the Internet via Wi-Fi or LTE.

• Sense Wi-Fi operate in the standard power mode, and will take accurate readings after approximately 2 hours.
• On LTE devices (such as Sense LTE or Glance LTE), the VOC sensor operates in an ultra-low power mode that pre-heats the element at a lower rate to preserve battery life. On these devices, allow up to 12 hours for the sensor to take accurate readings.

When you first turn on your device, you’ll see the VOC readings slowly increase while the element is heating up, until reaching a steady state.

If your sensor reboots (for example, after applying an over-the-air update), or is only turned off for a short time, it will retain its previous calibration state and the warm-up period does not apply.

Do I need to do anything to the sensors during this warm-up period?

No, you don’t need to do anything. Once you’ve turned your device on, the heating and calibration process will begin automatically.

What happens if the VOC levels exceed healthy thresholds?

It is usually best to look for spikes in VOC levels to find where problems may be occurring. If you see a spike, try to identify what happened at that time. Did someone use a cleaning product, or did you have a delivery of new furniture?

If your VOC levels seem like they are always high, the sensor may simply need recalibrating. Try turning it off for a while and then turning it back on again. You can also try taking it outside into the fresh air, and leaving it there for a while before bringing it back inside. Put another sensor in the same location to see if they both report the same readings.

Usually, you will see their trends and sharp spikes line up (a strong indicator for the presence of VOCs), while the absolute values can differ considerably.

By default, AirSuite notifications are enabled for temperature, CO₂ and VOCs. You will get a notification if VOCs exceed healthy levels.

To enable, disable or adjust thresholds, please refer to this support page.

I want to measure particles like mould spores, dust, or exhaust fumes. What do I need?

AirSuite offers particulate matter (PM) sensors as an optional add-on. It’s an extra little box which we plug in inside the device before we ship it to you. Ask for this add-on and we’ll do the rest.

Tell me more about PM - what does it mean?

A mix of solid particles and liquid droplets in the air, particulate matter or PM come in various sizes and compositions. The sources are both natural - like dust storms and forest fires - and human made - like emissions from factories, vehicles and construction sites.

Invisible to the naked eye, PM is categorised by size and measured in micrometres (µm).

The two most talked about are PM2.5 (combustion particles, organic compounds, metal, etc - particles with a diameter of 2.5 micrometres or smaller) and PM10 (dust, pollen, mould, etc - particles with a diameter of 10 micrometres or smaller).

The finer the particles, for example PM2.5, the greater the risk, as they can find their way deep into the respiratory system, including the lungs and heart, and even enter the bloodstream.

What do AirSuite PM sensors measure?

These sensors measure the mass and number concentrations of particles in the air like mould spores, dust and exhaust fumes. Different PM sizes are measured in categories like PM10 and PM2.5 (see above).

AirSuite devices contain an optical particle counting PM sensor. The sensor shines a laser through the air and measures the amount of light scattered by particles in the air. The more light scattered, the more particles are present.

All low-cost, consumer-grade PM sensors on the market today are optical particle counters. They are capable of measuring PM1 and PM2.5 with a level of accuracy that is acceptable for most applications, while PM4 and PM10 measurements are less accurate, because they are extrapolations from smaller particle measurements, based on typical aerosol profiles.

What’s the difference between mass concentration and number concentration?

Mass concentration represents the total weight of particles present in a given volume of air, measured in micrograms per cubic metre (µg/m³). This measurement provides information on the overall mass of particles, regardless of their individual size or number.

On the other hand, number concentration quantifies the actual number of particles within a given volume of air, regardless of their individual mass, expressed as the number of particles per unit volume of air. Mass concentration is the measurement typically referred to in most research and guidelines (e.g. those recommended by WHO).

The mass concentration and number concentration tend to be very closely correlated when there is a consistent distribution of particle sizes over time. But they can sometimes differ - when there is a moderate spike in mass concentration, but where the mass is dominated by small particles (e.g. PM1), the number of particles is likely to be higher.

How do I know if PM levels are healthy and safe?

High PM levels can indicate problems like mould growth or poor air quality. The World Health Organization (WHO) has recommended thresholds for safe daily PM exposure.

AirSuite provides recommendations on healthy range recommendations for each attribute measured by your AirSuite sensors on this support page.

What do WHO air quality guidelines recommend?

If you’re interested in some further reading - plus a breakdown on WHO’s updated air quality guidelines (as at 2021) - please visit their website, where you can read the full report, executive summary and more about air quality and health.

How do AirSuite’s PM sensors work?

Using a built-in fan, the PM sensors actively draw in surrounding air for measurement. This is different from VOC sensors which are passive.

The PM sensor takes readings every 15 minutes to avoid interfering with other sensors - running the fan moves the air around and could skew your other measurements slightly if it was on constantly.

How can I enable alerts for PM and what should I alert on?

First, follow our instructions to configure the thresholds, and enable organisation-wide notifications for PM2.5. We recommend alerting on PM2.5 instead of PM10, as PM2.5 measurements are more accurate.

Then, you can enable or disable email notifications for alerts triggered by devices in your organisation(s) in the My Account page of the Portal.

On this page, you can configure:

• Which organisations or specific deployments you receive alerts for
• Which category of alerts you receive (environmental or diagnostics)
• Whether you receive notifications at the ‘warning’ or ‘critical’ threshold, or both
• The delay (minimum continuous active time) before a notification is sent

How can I tell if mould levels are increasing?

If your PM10 level is really high, but your PM2.5 level is quite low, this can be an indication there is mould growth or mould spores in the air. On the other hand, if your PM2.5 levels are quite high, but your PM10 levels are relatively low, this is a sign you have a different problem.

How do I interpret the data?

While our sensor reports provide accurate, real-time information, they are not a substitute for expert analysis.

You can opt for reports which include colour-coded zones (green for good, red for bad) based on WHO recommendations.

Our readings are in the red zone. What should we do?

It depends on what’s happening in your space. If it’s a factory environment, the solution may be obvious like installing some extraction fans. If you’ve investigated the cause and the answer is not immediately clear, it could be worthwhile to consult a specialist who can advise you on the best course of action to improve your indoor air quality.

A specialist will take particulate matter samples and send them to a laboratory for analysis. This will help you identify the source of the problem and take the necessary steps to improve your indoor air quality.