Differential optical absorption spectroscopy, or DOAS, is a technique that is used to monitor pollutants in the atmospheric air. This form of spectroscopy is often used in continuous emission monitoring systems (CEMS).

Avantes instruments are integrated into a variety of CEMS around the world. Due to the high stability requirements of this technique, any of the Avantes thermo-electrically cooled spectrometers are used in this application.

Though it has been around for a few decades, nowadays DOAS is performed by recording two absorption spectra, one as a reference scan through a column of atmosphere (ideally) free of contaminants and one through an identical pathlength containing the contaminant that needs to be analyzed. The light traveling through the measured atmosphere is partially absorbed by trace contaminants along the way following Lambert Beer’s Law of Absorption.

Configuring a DOAS setup

With DOAS, UV/Vis absorption can be used to measure a wide range of molecular species with a single broadband light source. Not only does DOAS decrease the cost of multi-species detection, but it is also often far less expensive for single-species detection as well because of its use of inexpensive CCD spectrometers and a constant current D2 emission lamp, like our AvaLight-DHc deuterium halogen light source. In many cases, DOAS can even be performed using direct or scattered sunlight.

Because of their high stability requirements, a cooled spectrometer like the AvaSpec-ULS2048x64TEC-EVO is an ideal choice for DOAS applications. For less demanding DOAS applications, our AvaSpec-ULS2048x64-EVO and AvaSpec-ULS2048XL-EVO are great lower-cost candidates.


In this video we show you how DOAS can be applied in various applications. More videos and tutorials can be found on our support page or YouTube channel.

Why Avantes for your DOAS application?

  • Thermoelectrically cooled spectrometers for high stability
  • Constant-current light sources for long-term measurements
  • Fast and accurate measurements
  • Extensive knowledge on DOAS and CEMS applications

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Application Examples

Below are some detailed application notes on various uses of differential optical absorption spectroscopy in different applications and industries.

Related Products

These are some of the products mentioned above. To find the perfect setup for your specific application, contact one of our sales engineers for advice.