Nitrogen Oxides NOx

Aeroqual designs and delivers perimeter air quality monitors that measure nitrogen oxides (NOx).

Here we cover NOx measurement principles and specifications.

Overview of nitrogen oxides

Nitrogen oxides (NOx) are a group of gases (predominantly NO and NO2) that contribute to air pollution processes such as smog formation and ground level ozone production, both of which have detrimental effects on air quality and human health.

NO and NO2 are produced by combustion processes. The primary source of NOx emissions is the burning of fossil fuels in vehicles, power plants and industrial operations.


Perimeter air quality monitor

The NOx analyzer module features in our perimeter air quality monitor: AQM 65 Monitoring Station.

Measurement principle

The sensor used in the NOx module is a Gas Sensitive Semiconductor (GSS) manufactured by Aeroqual. The sensing material is a n-type semiconductor whose resistance increases when exposed to oxidizing gases such as NO2. A converter converts NO to NO2 which allows NO and NO2 to be measured and for NOx to be reported. The sensor also responds to ozone, so the air stream is passed through an ozone scrubber before reaching the sensor.

The NOx module uses Aeroqual’s patented automatic baseline correction (ABC) to measure NOx. The module uses two different flow paths, one of which passes through a proprietary scrubber to remove NO2 and produce a baseline measurement. The flow rate is determined by a flow control orifice on the exhaust side of the sensor and measured at the inlet to the sensor module (expected to be approximately 60 mL min-1). The sensor resistance is measured during both the zero and measurement states, and these values are used to calculate the NOx concentration using a proprietary algorithm, once per minute.

Module specifications

The NOx module performance specifications are given in the table below.

NOx Analyzer Module

Range (ppb)

0 - 500

Display Resolution (ppb)


Noise: Zero (ppb); Span (% of reading)

<1; 1%

Limit of Detection (ppb)



3% of reading or 3 ppb

Linearity (% of FS)


24 hr Drift: Zero (ppb); Span (% of FS)

1; 0.2%

Products that measure nitrogen oxides

The following products measure nitrogen oxides, as well as particulate matter and gaseous pollutants in real-time.

Inquire about our nitrogen oxides products

Our NOx advanced monitoring systems deliver hyper-local data and real-time alerts, giving you actionable data to make the decisions that matter.