Ad: The biggest leap in nitrogen oxides measurement technology since 1970s

Enviro Technology’s Duncan Mounsor discusses the revolutionary new Teledyne-API N500 CAPS True NOx – NO₂ – NO analyser, and why it’s the biggest development in ambient NOx monitoring since the 1970s.

That’s quite a claim, can you explain more?

Sure, for the past 40-50 years, we’ve been mainly measuring ambient concentrations of NOx using an ageing technology called chemiluminescence. This technique has been extremely successful and is based on a well-developed and widely accepted measurement technology that has become a ‘Gold Standard’ reference method around the world. But it has now been surpassed by newer and better ways of measuring NOx and in particular the regulated component of which limit values exist for, namely NO₂.

Really? So why are networks and local authorities still using older chemiluminescent NOx analysers today, in the 2020s?

That’s a good question. I think it comes down to several things. 1: Chemiluminescence is written into CEN standards as a reference method. 2: Air quality monitoring networks are very conservative and slow to change (unless a measurement technique is found to be seriously flawed as has been the case in the past with particulate measurement equipment). 3: The air quality community may not always be aware of the advances in non-chemiluminescence based instruments, and the choice of equivalent instruments that are now available.

 So, what’s wrong with chemiluminescence?

 Limitations of chemiluminescent NOx analysers include the fact that they don’t measure NO₂ directly (NO₂ being the most important component of NOx). NO₂ is instead calculated by subtracting the NO measurement from the NOx measurement, and evidence suggests that in some locations, chemiluminescent NOx analysers over-estimate NO₂ concentrations – not very good if measurements appear to be at, or close to, the 40 µg/m³ annual limit value!

 Also, because a reaction cell must be maintained under vacuum, a power-hungry external pump must be used. A typical chemiluminescent NOx analyser with external pump consumes approximately 0.5kW/h of electricity continuously, day in, day out. With electricity unit costs soaring, this is an awful lot of money. And finally, because of the switching time between NOx and NO measurement channels required for the calculation of NO₂, chemiluminescent NOx analysers tend to be quite slow in responding to fast changing concentrations of NO₂ which can be typical at some kerbside sites and in certain applications.

 Why do you think the new TAPI N500 CAPS NOx-NO₂-NO instrument is so disruptive and revolutionary?

 The N500 measures NO₂ (as well as NO and NOx) using one of the most exciting modern non-chemiluminescent technologies called CAPS, (Cavity Attenuated Phase Shift).

Without going too deeply into the physics, CAPS measures NO₂ directly and precisely using wavelength/molecule specific absorption. It’s an ‘absolute’ measurement, without any conversion or calculation, and as such, is less uncertain and potentially more dependable.

Significantly faster than chemiluminescence, inherently more precise and consuming a whopping 75% less energy per kW/h, the N500 CAPS brings massive operational cost savings in energy consumption alone. Not only does it use a fraction of the power of chemiluminescence NOx analysers, but it also requires considerably less servicing, and with in-built long life sample filters and automatic calibration checking, can pretty much do away with local site operator (LSO) visits.

 And lastly, and perhaps most importantly, in June 2022, the Teledyne-API N500 CAPS True NOx–NO₂–NO analyser became MCERTS approved. In short, it’s a real game-changer!

Find out more at ET.