Advanced Carbon‑Based NO₂ Sensor Enhances Indoor Air Quality Monitoring

Scientists have developed a highly sensitive and accurate nitrogen dioxide (NO₂) sensor that has lifesaving potential applications in domestic, public, and industrial settings. Long-term exposure to NO₂ — a major air pollutant that originates from combustion engines and industrial processes — can cause respiratory issues, which can be particularly severe and even life-threatening for babies and asthma sufferers. The gas sensor could provide accurate readings of NO₂ levels in the local environment in an affordable and portable Internet of Things device, which could sync with smartphones and applications.

Monitoring of air quality to prevent exposure to NO₂ at parts-per-billion (ppb) levels is currently only possible with unwieldy, expensive equipment and is therefore scarcely implemented. The goal of this work was to create a device that was sensitive and accurate enough to detect below 20 ppb of NO₂ in the air but that would also operate in real-world situations and be convenient and affordable enough to have the potential for widespread use.

The breakthrough came when the team developed an NO₂ sensing layer based on a laser-deposited carbon aerogel (LDCA), which they found to have exceptional selectivity towards NO₂ over other common air pollutants, making it unique amongst carbon nanomaterials. Using a scalable and inexpensive one-step laser process, the thin, porous, and well-adhered film of LDCA is deposited onto electrodes, which can then be housed in a range of device structures for continuous air monitoring. The sensor is so sensitive that it can detect close to 10 ppb of NO₂ in less than 15 minutes and crucially, can operate at room temperature — even performing well in humid conditions, a problematic environment for many other sensors.

Like condensation on a windowpane, nanomaterials such as the carbon used in this development, nearly always have surface water. Normally, this is a negative, as it interferes with the technology but in this case, the team was able to use the layer of water to their advantage to selectively dissolve NO₂ instead of other volatiles normally found in ambient conditions.

Potential applications for the sensor could include as a safety device to monitor the air quality in a baby's bedroom, to help inform the best walking or cycling routes and times of day to avoid high pollution levels, and even by real estate agents to provide prospective house buyers with information on the NO₂ levels in a home and area.

The data could also feed into a national or worldwide pollution monitoring database in order to effect positive action on air quality.