Indoor Air Quality
Know Your Indoor Air Quality to Improve Your Health and Productivity
When we think of "air quality", we tend to think of air pollution in the regions surrounding our homes. We rely on measures such as the Air Quality Index to let us know when airborne pollutants in our towns or cities reach levels that may cause or exacerbate health issues. When summer humidity brings an increased risk for asthma sufferers or when dangerous smog accumulates in cities, the message is simple: to protect your health, stay indoors.
However, some of the most polluted air we breathe is found indoors. From dust to formaldehyde to VOCs, unseen elements and particulate matter inside our homes and offices can cause both short- and long-term health issues. Given that people spend about 90% of their time indoors, measuring and controlling indoor air quality should be a top priority.
A growing body of research points to a link between COVID-19 cases and low humidity and/or high levels of pollution. Furthermore, high CO2 concentrations relate to virus infections.The higher the proportion of CO2, the higher the proportion of air that was breathed several times. And thus the risk of inhaling aerosols that another person in the same room has breathed out shortly before. The CO2 concentration is therefore a kind of indirect measurement for possible exposure to viral aerosols.
Being able to control and monitor these variables is therefore more important than ever.
Important Indoor Air Quality Indicators
CO2 is part of the human metabolism. It is produced when, for example, carbohydrates are metabolized to generate energy. The produced CO2 is then transported out of the body by respiration. The CO2 concentration in the inhaled air is decisive for the metabolism. Depending on the level of the concentration in the air breathed in, various symptoms can occur that affect daily life and health. High CO2 concentrations in the air we breathe lead to concentration problems and fatigue. The performance potential of people in the room decreases constantly the higher the amount of CO2 in the air gets. Furthermore, CO2 concentrations relate to the potential of virus infections.
The level of CO2 in the air can be thought of as a "traffic light" system: Green is between 400–1'000 ppm; yellow is between 1'000–1'600 ppm and is where 80% of people are satisfied with perceived air quality; red is ≥1'600 ppm and is where there are detectable negative impacts on human health and well-being. At this level, the air quality is considered poor and the risk of viral transmission is increased.
Humidity and Temperature
Do you find it hard to breathe in your home some days? Are you more prone to headaches and asthma attacks during the summer months? You’re not allergic to heat - but you may have serious humidity problems in your home or office. When we talk about indoor air quality, humidity is one of the main things we’re referring to. Too high or too low humidity levels in closed spaces can lead to various issues. For example, bacteria and viruses that cause respiratory infections thrive in extremely high and extremely low humidity. Mold spores, dust mites and other allergens survive best in high humidity environments. Furthermore, higher humidity can increase the levels of noxious chemicals in the air, which may include ozone and formaldehyde.
40-60 % relative humidity is an optimal level for the immune system and our respiratory system. It reduces the spread of seasonal respiratory diseases and increases well-being. Scientists are therefore calling on the WHO (World Health Organization) to revise the global guidelines for indoor air quality with the petition 40to60RH. Click here to learn more about it.
Volatile Organic Compounds (VOCs)
VOCs originate from a number of different possible sources, like building materials, tobacco smoke, people and their activities, and indoor chemical reactions. Most common VOCs include benzene, ethylene glycol, formaldehyde, methylene chloride, tetrachloroethylene, toluene, xylene, and 1,3-butadiene. Exceptionally high VOC levels are typically found in new buildings or after renovation. Further, when using products that contain VOCs, such as air fresheners or cleaning agents, people expose themselves and others to high pollutant levels that can persist long after the activity has finished. A number of systematic human exposure studies have shown various adverse health
effects caused by exposure to elevated VOC levels. Among the effects reported by participants are dryness and irritation of the eye, the nose and the throat, headaches, and dizziness.
Sensirion’s powerful VOC Algorithm analyzes VOC events detected by the SGP40 sensor and maps them to a VOC Index. This VOC Index provides a practical quantification of VOC events relative to each individual sensor’s typical indoor environment. In this way, it behaves similarly to the human nose, which is highly susceptible to changes in odor, but it also detects VOC events that are not perceived by humans. The VOC Index indicates to what extent the indoor air quality has deteriorated or improved compared to the sensor’s typical VOC environment. Learn more about the VOC index at www.sensirion.com/sgp40.
Particulate Matter (PM2.5)
Particulate Matter (PM) is a complex mixture of solids and aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. Particles are defined by their diameter for air quality regulatory purposes. Those with a diameter of 10 microns or less (PM10) are inhalable into the lungs and can induce adverse health effects. A number of adverse health impacts have been associated with exposure to PM2.5. Short-term exposures (up to 24-hours duration) have been associated with premature mortality, increased hospital admissions for heart or lung causes, acute and chronic bronchitis, asthma attacks, emergency room visits, respiratory symptoms, and restricted activity days.
Indoor PM levels are dependent on several factors including outdoor levels, infiltration, types of ventilation and filtration systems used, indoor sources, and personal activities of occupants. In homes without smoking or other strong particle sources, indoor PM would be expected to be the same as, or lower than, outdoor levels. To know what the limits of PM exposure are, please consider official air quality standards. The US Environmental Protection Agency defines the AQI levels as follows: With regard to primary (health-based) standards for fine particles (generally referring to particles less than or equal to 2.5 micrometers (μm) in diameter, PM2.5), the EPA is revising the annual PM2.5 standard by lowering the level to 12.0 micrograms per cubic meter (μg/m3) so as to provide increased protection against health effects associated with long- and short-term exposures (including premature mortality, increased hospital admissions and emergency department visits, and development of chronic respiratory disease), and to retain the 24-hour PM2.5 standard at a level of 35 μg/m3.
Formaldehyde (chemical formula H2-C=O or often HCHO) is a colorless gas and the simplest organic molecule containing C, O, and H. It is highly reactive and has several natural and man-made sources. Formaldehyde is actually a VOC (mentioned above) and is one of the most common VOCs that are harmful in the home. Formaldehyde concentrations are much higher indoors than outdoors and hence formaldehyde is qualified as a very specific indoor pollutant.
The most significant sources of formaldehyde are likely to be pressed wood products such as particleboard, plywood, or medium-density fiber board (MDF) made using formaldehyde-based resins. These materials are frequently used as sub-flooring and shelving and in cabinetry and furniture. Elevated formaldehyde concentrations can be present in freshly built, furnished, or painted rooms for months.
In relevant concentrations, formaldehyde is a pungent-smelling gas, can cause watery eyes, burning sensations in the eyes and throat, nausea, and difficulty in breathing. Sensory irritation by formaldehyde has been reported for concentrations as low as 0.15 mg/m3 (120 ppb). High concentrations may trigger attacks in people with asthma. There is evidence that some people can develop a sensitivity to formaldehyde. It has also been shown to cause cancer in animals and formaldehyde is classified by IARC as carcinogenic to humans (Group 1).
Guidelines and Standards
The WHO has established an indoor air quality guideline for exposure to formaldehyde of 0.1 mg/m3 (80 ppb) as a 30-minute average. Local guidelines range from 8 ppb to 100 ppb depending on the environment and duration of exposure
Indoor Air Quality Applications
|Air Treatment Devices|
Air Purifiers / Air Conditioners / PTAC
Vent Hoods / Fume Hoods
Humidifiers / Dehumidifiers
|Air Monitoring Devices|
Indoor Air Quality Monitors
Wall Mount Sensors
Mobile Phones / Consumer Electronics
How Can You Improve Your Indoor Air Quality?
To improve your indoor air quality, it is important ot know about your air quality conditions so that you can properly maintain your home and work spaces with smart actions such as source control, changing filters, investing in air purifiers, letting fresh air in etc. (Source: Havard Health Publishing). That's where Sensirion steps in. With our market leading environmental sensor solutions, we enable precise and accurate monitoring of these air quality indicators. By having a smart ventilation system / routine or by using air treatment devices such as air purifiers or air conditioners with fresh air exchange, you can improve your air quality, increase your health and minimize the risk of virus infections.
Overview Environmental Sensors
|Carbon Dioxide (CO2) Sensors|
|The SCD4x is Sensirion’s next generation miniature CO2 sensor that offers an unmatched price-to-performance ratio. SMD compatibility and the small footprint allow cost- and space-effective integration to boost freedom of design for customers. The integrated best-in class humidity and temperature sensor enables superior on-chip signal compensation and addition RH and T outputs.||In line with Sensirion’s industry-proven humidity and temperature sensors, the SHT40 offers the best price-performance ratio on the market. The SHT40 offers reduced power consumption and improved accuracy specifications. With the extended supply voltage range from 1.08 V to 3.6 V, it’s the perfect fit for mobile and battery-driven applications.||SGP40 is Sensirion’s new digital VOC (volatile organic compounds) sensor designed for easy integration into air treatment devices and air quality monitors. In combination with Sensirion’s powerful VOC Algorithm, the sensor signal can be directly used to evaluate indoor air quality, e.g., for triggering the gradual fan control of an air treatment device.||The MCERTS-certified SPS30 particulate matter (PM) sensor marks a new technological breakthrough in optical PM sensors. Its measurement principle is based on laser scattering and makes use of Sensirion's innovative contamination-resistance technology. This technology, together with high-quality and long-lasting components, enables precise measurements from the device's first operation and throughout its lifetime.||The SFA30 is Based on Sensirion’s electrochemical technology and offers excellent formaldehyde sensing performance with a uniquely low cross-sensitivity to other VOCs. The sensor module’s on-board SHT sensor provides accurate humidity and temperature readings and enables a fully temperature/humidity compensated and factory calibrated formaldehyde concentration output in ppb.|
Glow C is an air quality monitor, smart plug and smart nightlight all in one. It monitors indoor temperature, humidity, and airborne toxic chemicals (VOCs) and provides users with real-time insight into their air quality via the Awair app. In addition to monitoring air quality, Glow C’s smart plug can automatically trigger an attached device (such as a humidifier, air purifier or fan) to resolve air quality issues the moment they arise. At night, Glow C doubles as a smart nightlight with customizable color settings and motion triggers.
The direction to increase occupant comfort and productivity has led to the development of new, innovative thermostat and sensor fused technologies that contribute significantly to improving air quality, while relying on Sensirion’s SCD30 CO2 sensor and SHTC3 digital humidity and temperature sensor. The O3 Sensor Hub in particular detects motion, sound, light, humidity, and temperature, and is perfectly designed to fit the most urgent consumer needs.
“Thanks to Sensirion’s high-quality and extremely accurate environmental sensors, the LAIR ONE provides reliable air quality measurements combined with a refined user experience,” says Hamedo Ayadi, CEO at LAIR GmbH’s software provider Intelligent Data Analytics GmbH & Co. KG.
"Thanks to the sensor from Sensirion, we can ensure that CARU air determines CO2 concentrations accurately and reliably", says Susanne Dröscher, Co-CEO of CARU AG. "We are glad to have found in Sensirion a Swiss supplier that guarantees our high standards of quality and reliability."
"Sensirion is clearly an industry leader when it comes to digital sensors and their VOC sensors are perfect for our devices owing to their small size, stability, and accuracy. We’re thrilled by the sensors’ quality and the ease with which we have been able to integrate them into our products,” says Kevin Cho, CTO & Co-Founder at Awair.
“Sensirion’s ability to cost effectively, package high precision sensing technology in a tiny footprint has allowed us to design sensor rich devices capable of providing more accurate, faster and smarter feedback of the conditions of a monitored space.” says Delta Control’s Product Manager, Gamal Mustapha.
An air sensor that not only monitors CO2 but also the VOC concentration in enclosed areas, as well as the temperature and humidity. LAIR ONE thus covers the four most important factors for air quality and lets the user know when fresh air is needed thanks to its discreet yet clearly visible ambient status light. With its small size, modern design and high-quality manufacturing, it not only fits in any living room or office, but also works perfectly in restaurants or schools.
Thanks to CARU air, ventilation is built into everyday life. The CO2 measuring device CARU air works like a traffic light, indicating when it is time to ventilate: at the earliest, yellow (1000 - 1399 ppm CO2) and at the latest, red (> 1400 ppm CO2). Since a few weeks, the first CARU air units have been installed in selected schools, offices, medical practices and retirement homes. The feedback: positive all around!
How do I understand the RH response time of 8s? Is that the time I have to wait before I take my first measurement after powering the sensor?
It is the time taken to achieve 63% of a step function, in this case given by a humidity step from 10% RH to 90% RH. The value of 8s is valid at 25°C and 1m/s airflow. At lower temperatures, the response time will be slower; at increased temperatures, the response time will be faster. The sensor adapts to ambient conditions even without power.
Do you have a chemical sensitivity chart for our reference?
As with all polymer-based capacitive humidity sensors, SHTxx sensors are sensitive to chemicals. Sensirion does not have a chemical sensitivity chart. Compliance with the handling instructions is recommended to ensure correct functioning of the sensor.
Beside the substance itself, the duration of exposure, the concentration of the contaminating substance and the temperature are critical to contamination. As a rule of thumb, the air one can breathe over a long period without any harm to health is not expected to contaminate the SHTxx.
I measure a deviation of temperature from a test sensor to my reference. What could be the cause?
If a temperature deviation is observed, please be aware that an out-of-specification deviation must be larger than the sum of the specified accuracy tolerances of the tested sensor and reference sensor. Make sure the reference is working well.
The possible causes of such an effect may include heating or cooling elements close to the sensor, too many subsequent measurements (self-heating), a housing that slows down the response time, the use of wires to connect the sensor, or a missing decoupling capacitor between VDD and GND.
Possible solutions might include disconnection of the sensor from the heating element by adding slits into the PCB, or connecting the sensor only with narrow bridges to the rest of the PCB. Make sure the sensor is not mounted directly on to heat sources or heat sinks. Reduce sampling. Shorten the cables and/or use a decoupling capacitor (typ. 100nF) between VDD and GND pins of the sensor as close as possible.
Guidelines for sensor implementation can be found in the Design Guide.
Can I use your humidity sensors to measure absolute humidity?
Not directly. Our sensors measure relative humidity, but relative humidity values can be converted to absolute humidity or dew point if needed. Please see application note 'Humidity at a Glance', available in the Download Center, for more details.??
What is the best way to verify your humidity and temperature sensors?
Please refer to our Testing Guide Humidity to learn how the sensor's performance can be verified. The document can be found in the Download Center on our Website.
Are SCD30 factory calibrated?
Yes, all SCD30 are factory calibrated. However, a NDRI based CO2 sensor is a delicate optical instrument. Mechanical stress during handling and assembly can offset the sensor. Apply the Forced Recalibration (FRC) or Automatic Self Calibration (ASC) procedure to correct such offsets.
Ideally, a sensor calibration is performed after sensor installation, to compensate for potential mechanical stress during installation.
What is the definition of CO2eq?
The CO2 equivalent (CO2eq) is an estimation of the CO2 concentration based on a H2 measurement. The SGP30 provides a signal which is calibrated to Hydrogen (the H2_signal). Based on empirical correlations between H2 and CO2, a conversion factor between H2 and CO2 has been determined. The CO2eq output is finally given by the measured H2 concentration and the empirical conversion factor.
What is special about the Sensirion Multipixel Gas Sensor?
- Outstanding long-term stability
Siloxane-resistant metal-oxide gas sensor. Siloxanes are the main reason for MOx sensor sensitivity degradation. They are found in most real-life applications due to their widespread use in many consumer product e.g. silicon, cosmetics and so on.
- Easy integration:
- small 2.45x2.45x0.9mm3 DFN package
- The sensor provides calibrated indoor air quality signals over an I2C interface
- on-chip humidity compensation
- Multi-pixel platform
The SGP features a multi-pixel platform integrating 4 sensing elements into one DFN package. This improves selectivity and long-term stability of MOx gas sensors. Currently, the multi-pixel platform offers tVOC and H2-based CO2eq air quality Signals.
- Every SGP sensor is individually calibrated during production. No calibration is required by the customer.
What is the recommended production line test?
The SGP features an on-chip self-test which is recommended for production line testing. This test will ensure proper electrical connection of the SGP and that the sensor was not damaged during mounting. To run such a test, the Sensirion SGP gas sensor comes with an on-chip self-test. The “Measure_test” command, as described in the datasheet, starts the self-check and will return “0xD400” if all internal tests were passed. It is that simple.
What is the IP protection level of the SGP?
The SGP features a dust and water protection membrane that makes it robust against water and dust in consumer device applications. However, the SGP does not have an IP level specification.
What is the humidity cross-sensitivity of the SGP sensor?
All MOX sensors including the SGP show a certain cross-sensitivity to humidity.
The SGP30 and the SGPC3 feature an on-chip humidity compensation for the air quality signals and the raw signals. To use the on-chip humidity compensation an absolute humidity value from an external humidity sensor like the SHTxx is required.
Which gases does the SGP gas sensor measure?
Metal-oxide based gas sensors are sensitive to a broad range of gases like H2, CO, VOCs (Alcohols, Aliphatic Hydrocarbons, erpenes, Aromatic Hydrocarbons, Ketones, Esters,…), NO2,…
For indoor air quality application, the SGP is optimized for the detection of VOCs and H2. MOx sensor are not sensitive to CO2.
The sensitivity to different gases can be modified by material engineering, e.g. by changing the sensing material or adding certain doping materials and by changing the operation temperature of the sensor.
What is the expected life time of the SGP?
The main limitation for the life time of traditional MOx sensor is contamination by Siloxanes. With the SGP, Sensirion has solved the Siloxane degradation problem of MOx sensors. Accelerated Siloxane degradation tests performed as part of the qualification of the SGP ensure the stability of the sensor for more than 10 years in indoor conditions. In addtion, stress tests at high temperatures and humidities are performed as part of the qualification of the SGP.
To ensure the reliability of the ASIC and the package of the SGP Sensirion performs an extensive set of accelerated life-time test according to JEDEC specifications. These tests ensure sensor reliability for 10 years of operation.
Particulate Matter sensors (PM)
Where can you find particulate matter?
Particulate matter can be found in In indoor and outdoor environments.
- It is common to find PM sources like spray or smoke (cigarette, candle, incense, etc…).
- A very common source of PM is also dust. The usual dust that everyone knows, which can be seen by shaking a mattress or on the surface of furniture when we didn’t clean our place for some time. This dust can be also seen by the bare eye, when a sunlight enters our home through a window and we see many particles flying through it.
- Cooking might also generate many particles. Boiling oil creates quite high PM concentrations in the air.
In outdoor environments, PM is normally generated through the combustion of solid and liquid fuels, such as for power generation, domestic heating and in vehicle engines.
In towns and cities, emissions of PM2.5 from road vehicles are an important source. Consequently, levels of PM2.5 (and population exposure) close to roadsides are often much higher than those in background locations.
In some places, industrial emissions can also be important, as can the use of non-smokeless fuels for heating and other domestic sources of smoke such as bonfires. Under some meteorological conditions, air polluted with PM2.5 from mainland may circulate over neighboring islands or land – a condition known as the long-range transportation of air pollution.
What is the difference between PM2.5 and PM1 and PM10?
The number “x” in PMx stands for particle diameter smaller than “x” micrometers. PM2.5 defines thus inhalable particles with diameters that are generally 2.5 micrometers and smaller. PM10 defines thus inhalable particles with diameters that are generally 10 micrometers and smaller.
What is particulate matter?
PM is a mixture of airborne solid particles and liquid droplets. It can be inhaled and cause serious health problems. The smaller the particles are, the deeper they can penetrate through our breathing into the respiratory system and into the bloodstream. Historically, PM-values are measured in μg/m3
It has been proven that indoor humidity plays an important role in preventing virus transmission and improving the response of the immune system. Extensive research shows that a relative humidity (RH) between 40% and 60% is optimal to minimise the spread of viruses such as influenza. Scientists are therefore calling on the WHO to revise the global guidelines for indoor air quality.
The importance of indoor humitidy is crucial to us. As market leader in humidity sensing it is important to us to support petition 40to60RH. Improving people's health is part of our mission and therefore we encourage everyone to support this petition to gain the attention of the World Health Organization.
Support the petition and learn more about it: www.40to60rh.com
Ventilate indoor spaces regularly and thoroughly - this is recommended by the Federal Environment Agency to reduce the risk of Sars CoV-2 infection. This announcement is particularly relevant in view of the fact that the school has started again at full class size. For this reason, the supply of fresh air in the classrooms should also be as high as possible, regardless of other protective measures such as keeping minimum distances or wearing a mouth-and-nose cover. After all, droplets and tiny aerosol particles should play a decisive role in the transmission of Sars-CoV-2. Especially the aerosol particles that are produced when breathing, coughing, speaking and sneezing can float in the air for hours or days, according to current knowledge. Consistent ventilation can significantly reduce the risk of infection, but cannot provide 100% protection.
Upcoming SEN55 Sensor Combo Module: All-In-One Air Quality Sensing!
Are you interested in a sensor combo module measuring humidity, temperature, VOCs, particulate matter and oxidizing gases (NOx and O3)? We published a preview of our upcoming SEN55 combo sensor module - click here to learn more.
If you are planning to develop an air quality monitor or air quality treatment device, Sensirion is your partner of choice. Feel free to already contact us to get more information about the upcoming SEN55 environmental sensor node!
Benefits of designing in SEN55 into your application:
- Less costs on supplier management & logistics
- Less R&D costs and time
- Lower BOM costs
- Lower assembly costs easier & faster design in (mechanical & software)