Low-cost gas-sensitive electrochemical (GSE) nitrogen dioxide (NO2) sensors are used for both indoor and outdoor monitoring. The sensors are stable, long lasting, require very little power and are capable of accurate measurement. These features mean they are often used in compact devices for monitoring outdoor air pollution measurements where NO2 is a criteria pollutant of interest.
However, GSE NO2 sensors are susceptible to cross-interference from ozone (O3) when measuring the outdoor air. We have tackled this issue by developing a new 0-1 ppm nitrogen dioxide (NO2) sensor head that contains an integrated ozone (O3) filtering layer. This gives you an accurate way to measure the air, by removing the ozone interference.
The challenges of measuring nitrogen dioxide (NO2)
Nitrogen dioxide sensors are susceptible to temperature (T), relative humidity (RH) and interfering gases, particularly ozone. These factors can all impact the NO2 measurement. We discuss the challenges with electrochemical NO2 sensors in more detail in this blog. This cross-interference with ozone reduces the usability of the NO2 sensor head, as an adjacent ozone reading is required to produce an accurate NO2 measurement.
Solutions to nitrogen dioxide cross-sensitivity
There are two main ways to reduce the effect of cross-sensitivity on electrochemical nitrogen dioxide sensors:
- Correcting for the ozone interference by using Aeroqual’s selective gas-sensitive semiconductor (GSS) ozone sensor technology alongside a GSE NO2 sensor. Our AQY micro air quality monitor overcomes these challenges by using an Aeroqual patented technique.
- Using selective filters (chemical scrubbing). This technique is used in our new filtered NO2 sensor head, creating a single sensor solution for our versatile portable monitors.
How does the new filtered NO2 sensor perform
Let’s take a look at how the new filtered nitrogen dioxide sensor performs. The following charts show the effect of the filtering layer we have used in the NO2 sensor. They also compare the performance of the new 0-1 ppm NO2 sensor head (with ozone filter) with the previous unfiltered NO2 sensor head. All data below is using 15-minute time averaged data.
In the chart above you can see how the old unfiltered NO2 sensor head responds to both ozone and NO2. When the ozone (purple) levels are high, the sensor is reading high. When but it is also responding to the ozone. This means that the reading you are getting is not an accurate NO2 measurement by itself.
In the chart above you can see the new filtered nitrogen dioxide sensor no longer responds during the periods of high ozone (purple). This means the NO2 reading of this sensor head is much more accurate out of the box and it no longer requires a secondary measurement or data source to be correct.
What products does the new sensor work with?
The new filtered NO2 sensor head is compatible with the following Aeroqual products:
Here are some case studies of how Aeroqual portable monitors have been used with NO2 sensors.
- Johns Hopkins University study on household air pollution (HAP) from biomass cookstoves
- University of Birmingham daily personal NO2 exposure study
- RSK Group Ltd for an Environmental Impact Assessment (EIA)
Aeroqual also offers the new filtered NO2 measurements in the following products:
St. John is responsible for supporting Aeroqual’s diverse international customers and representatives to provide each with tools to help them understand the air they breathe. With experience across a range of industries and an industrial design background, he regularly adds a bit of “colour” to the marketing and strategic direction for his range of products.