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Altech Environmental

NOx - Nitrogen Oxides Monitoring Analyzer

Altech offers all the common solutions for the continuous monitoring of NOx (NOx CEMS). Since 1989, we have successfully installed over 2000 NOx continuous emissions monitoring systems worldwide.

We measure NOx using a discrete analyzer or as part of a multi-gas analyzer. With the MIR 9000 series multigas analyzers, it’s as simple as a configuration/programming change to decide which parameters are measured by the CEMS. CEMS systems measure NOx using dilution extractive, cold/dry or hot/wet direct extractive sample systems. NOx is also measured in ambient air monitoring systems.

One of the three following methods is used to measure NOx:

In Altech’s flagship MIR 9000, MIR-IS and MIR 9000H analyzers, non-dispersive infrared technology (NDIR) using the Gas Filter Correlation (GFC) technique is used to measure NO and in some applications NO2. The infrared bench consists of a light source, chopper, multipass sample cell, filter wheels, and solid-state detector (see Figure 1). The filter wheel containing the optical filter and gas cells provides a dual function. One is to modulate the light; the second is to isolate the wavelengths for measurement. This configuration provides for a much simpler optical and mechanical system. The modulated light is sent into a temperature stabilized (50ºC) multipass sample cell. Depending on the application, NOx can be measured as NO, NO+NO2, or total NOx by passing the sample through an NO2-NO converter so that the entire NOx sample is converted to NO. The MIR 9000 is available in cold/dry and hot/wet configurations.

In our MIR 9000CLD (Chemiluminescence Detector) and Topaze 32M analyzers, the proven chemiluminescence detection principle is used to attain low NO, NOx and NO2 measurements while maintaining stability of the measurements. The analyzer measures the luminescent signal generated by reacting NO with Ozone. The signal is detected with a temperature stabilized photomultiplier tube. The fast switching time plus special software algorithms minimizes negative NO2 artifacts. Excellent measurement stability is achieved through the use of temperature controlled critical orifices for sample flow. The CLD portion is a dry basis analyzer and the Topaze 32M is available in cold/dry or hot/wet configurations.

In our MIR FT analyzer, Fourier Transform Infrared spectroscopy is used. Fourier transform infra-red spectroscopy is a variant of infra-red absorption spectroscopy. Rather than measuring the absorption of each narrow band of wavelengths consecutively to generate an absorption spectrum, the amount of light from a broad band source transmitted through a scanning interferometer is measured as a function of interferometer optical pathlength. The Fourier transform of this is the absorption spectrum. FTIR analyzers are generally supplied in a hot/wet configuration.

Contact Altech for any questions you may have related to NOx CEMS or NOx analyzers at 630.262.4400 or Since we offer all common NOx measurement technologies and analyzer manufactures (if you require a specific manufacturer or model). Altech tailors its system offering to your specific application – Altech’s instruments that measure NOx are as follows:

Emission Monitoring

Air Quality Monitoring

Engine Gas Monitoring