Using Sensors to Accurately Measure Formaldehyde

Formaldehyde is volatile, widely used, and associated with a variety of health issues. As a result, it is a significant indoor air pollutant, but measuring formaldehyde concentrations accurately and easily has long proven difficult due to issues with cross-sensitivity in detectors.

This article examines the risks associated with formaldehyde and analyzes how the SFA30 formaldehyde sensor offers a higher level of selectivity in formaldehyde detection.

Formaldehyde 101

While most refer to it as a biology-class preservative or embalming agent, formaldehyde is actually one of the most important basic industrial chemicals in the world. In reality, it is estimated that over 18 million tons of formaldehyde are produced on an annual basis.¹

As an important precursor, formaldehyde is highly versatile and used to manufacture thousands, if not millions, of consumer and industrial products. One application area that uses the most formaldehyde is the production of resins, which have many applications.

Formaldehyde resins are mostly used to make particle boards, plywood, and furniture. In addition, they are also used as auxiliary materials in the cement, leather, rubber, and surface coatings sectors and the manufacturing of controlled-release nitrogen fertilizers, curable plastics, and surface coatings. Due to its exceptional functionality, it is rare for other chemicals to be used in place of formaldehyde in these applications.

Image Credit: Shuttestock.com/sulit.photos

A Dangerous Air Pollutant

Initial concerns regarding formaldehyde as a dangerous air pollutant first began in the 1960s when inhabitants of prefabricated houses started to report adverse health effects, including irritation of the eyes and airways.² It was soon determined that formaldehyde emissions from particleboards bonded with formaldehyde resins were to blame.

Although formaldehyde is produced by the body naturally, breathing it in can be hazardous. Chronic exposure is associated with various health issues, including asthma and cancer, and can irritate the eyes and airways when concentrations exceed 0.1 ppm.

The CDC classifies formaldehyde as a systemic toxin, and safety and occupational health organizations across the globe have established acceptable exposure thresholds for formaldehyde in both occupational and non-occupational situations.^3,4

Part of the problem is that, at room temperature, formaldehyde is a gas. This means that small amounts of free formaldehyde in resins are prone to evaporate into the surrounding air, potentially reaching harmful concentrations. Due to the ubiquity of formaldehyde in building materials and consumer products, this is especially problematic indoors, with wood-based materials, insulation materials, coatings, and flooring representing a significant hazard.

There are, however, a few ways to reduce the risk of formaldehyde exposure. The optimum strategy, of course, is to eliminate sources before they become an issue. For instance, several groups promote the use of low-emitting materials in construction.⁵

Of course, given how many everyday items and products contain the chemical, eliminating formaldehyde sources is not always feasible. Simple ventilation solutions, such as installing ventilation systems in industrial environments or just opening windows, can efficiently reduce levels of formaldehyde (and other air pollutants) in areas where sources already exist.

The only real approach to guarantee safety, as with any gas hazard, is to use instruments that can measure the levels of formaldehyde in the air.

Formaldehyde Sensing

The World Health Organization recommends a 0.08 ppm exposure limit to avoid health issues, including sensory irritation.⁶ Yet, creating viable sensors that can detect formaldehyde concentrations in this range has proven challenging.

One of the main challenges that formaldehyde detectors face is selectivity: sensors geared toward detecting formaldehyde are typically sensitive to other VOCs, which commonly occur at much higher concentrations in indoor environments.

The accuracy with which formaldehyde can be detected takes a hit outside the lab due in no small part to the huge variety of VOCs in typical indoor environments. Present in ppm concentrations, many of these VOCs can fool formaldehyde sensors into registering higher levels of formaldehyde than are actually present in the air.  

For a long time, only spectroscopic devices have been able to reliably achieve accurate measurements of formaldehyde at concentrations of interest – however, these devices are typically expensive, difficult to transport and complex, rendering them unsuitable for most monitoring applications.

The SFA30 Formaldehyde Sensor from Sensirion

The SFA30 is an electrochemical formaldehyde sensor specifically designed to fulfill the need for fast, accurate, and simple formaldehyde detection in any environment.⁷ Engineered for formaldehyde selectivity, the sensor provides extremely low cross-sensitivity to other VOCs (less than <0.2% for ethanol).

The SFA30 has exceptional accuracy when exposed to volatile organic compounds (VOCs), which are prevalent in most residential and commercial environments. This feature reduces false positives and increases the sensor’s lifespan. The SFA30 is notable for having a low cross-sensitivity to ethanol, which causes errors in similar sensors.

The integrated humidity sensor and thermometer in the SFA30, designed to work in any environment, allow a specially-created algorithm to account for the effects of moisture and temperature on the sensing element. The SFA30 features anti-dry technology to ensure the liquid electrolyte's longevity and long-lasting stability over a six-year lifetime.

Versatile mounting options, in combination with selectable digital UART and I2C interfaces, also mean that the SFA30 can be effortlessly integrated into devices such as air conditioners, air purifiers, and indoor air quality monitors.

References and Further Reading

1. Franz, A. W. et al. (2016) Formaldehyde. in Ullmann’s Encyclopedia of Industrial Chemistry (ed. Wiley-VCH Verlag GmbH & Co. KGaA) 1–34 (Wiley-VCH Verlag GmbH & Co. KGaA, 2016). doi:10.1002/14356007.a11_619.pub2.
2. Salthammer, T., Mentese, S. & Marutzky, R. Formaldehyde in the Indoor Environment | Chemical Reviews. Available at: https://pubs.acs.org/doi/10.1021/cr800399g
3. Formaldehyde | Medical Management Guidelines | Toxic Substance Portal | ATSDR. Available at: https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=216&toxid=39
4. Formaldehyde | Medical Management Guidelines | Toxic Substance Portal | ATSDR. Available at: https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=216&toxid=39
5. US EPA, O. ANSI/ASHRAE/USGBC/IES Standard 189.1-2014: Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings (ASHRAE 189.1). https://www.epa.gov/smartgrowth/ansiashraeusgbcies-standard-1891-2014-standard-design-high-performance-green-buildings (2014)
6. Kaden, D. A., Mandin, C., Nielsen, G. D. & Wolkoff, P. Formaldehyde. WHO Guidelines for Indoor Air Quality: Selected Pollutants (World Health Organization, 2010)
7. SFA30 Formaldehyde Sensor Module | Sensirion. Available at: https://www.sensirion.com/en/environmental-sensors/formaldehyde-sensor-sfa30/

This information has been sourced, reviewed and adapted from materials provided by Sensirion AG.

For more information on this source, please visit Sensirion AG.