Blue Light – the new way of analysing NOx at Auchencorth Moss

NO_x compounds are oxides of nitrogen, generally considered to be Nitric Oxide (NO) and Nitrogen Dioxide (NO₂). Primary emissions of NO_x are predominantly from combustion, such as vehicle exhaust emissions. But, NO_x is also formed in the atmosphere, by NO reacting with Ozone (O₃) to form NO₂ and Oxygen (O₂) – these are Secondary emissions. With some engines known to be exceeding official pollution limits in ‘real world’ running conditions, NO_x and its human health impacts, specifically respiratory issues, have moved up the policy agenda once again.

At Auchencorth Moss we have measured NO_x for over 20 years using a standard thermal conversion technique. This method uses a heated molybdenum catalyst to convert NO₂ to NO for analysis. This thermal conversion technique poses issues: what about other atmospheric compounds that may be thermally broken down to NO? This method therefore has the potential to overestimate NO₂ concentrations, by thermally breaking down NO_Y (other oxides of nitrogen, such as Nitric Acid) into NO for analysis.

In order to overcome this issue we have deployed an instrument which should meet the EMEP and ACTRIS standards, a Teledyne T200UP, Blue Light converter. Instead of breaking down NO₂ into NO thermally, this method uses a specific wavelength of (blue!) light to do it photochemically. This wavelength is specific for breaking down NO₂ and therefore minimises interferences from NO_Y, thereby providing more accurate NO₂ data. In 2016 a new auto-calibration system will be implemented.

This new analyser will allow us to compare our thermal and blue light converted NO₂ data. This will mean we can more accurately report NO and NO₂, as well as quantify the NO_Y fraction. This follows on from, and comprises a significant element in our previous work to describe a Nitrogen Budget for Auchencorth Moss.  Other work includes comparison with new low cost sensors to determine their reliability and accuracy.

Our data will be submitted as part of the EU ACTRIS II project to the EBAS database.

Relevant weblinks:

• Blue light converter signals way forward for NO2 Measurement
• Diesal car pollution
• EMEP monitoring strategy

For further information please contact John Kentisbeer.

Figure 1: Plot of NO and NO₂ data from the Blue Light instrument at Auchencorth Moss.