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

NOx compounds are oxides of nitrogen, generally considered to be Nitric Oxide (NO) and Nitrogen Dioxide (NO2). Primary emissions of NOx are predominantly from combustion, such as vehicle exhaust emissions. But, NOx 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, NOx and its human health impacts, specifically respiratory issues, have moved up the policy agenda once again.

At Auchencorth Moss we have measured NOx 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 NOY (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 NOY, 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 NOY 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:

For further information please contact John Kentisbeer.

Blue Light NOx data plot

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