MetNO2 project leader, Dave Worton from NPL has published an opinion article entitled “Future Adoption of Direct Measurement Techniques for Regulatory Measurements of Nitrogen Dioxide: Drivers and Challenges” in the Viewpoint section of the American Chemical Society’s Journal of Environmental Science and Technology (https://pubs.acs.org/doi/pdf/10.1021/acs.est.0c04709).

This article describes the important of atmospheric nitrogen dioxide (NO₂) and that as a result of the chemiluminescence (CLD) measurement technique typically used to demonstrate regulatory compliance it remains the only regulated air pollutant that is not directly measured or calibrated. With the CLD method the NO₂ amount fraction is estimated as the difference between two channels, one that measures NO only and the other that measures total nitrogen oxides (NO_x = NO + NO₂) after NO₂ is either catalytically or photolytically converted to NO prior to detection. Interferences in the NO_x channel from other reactive nitrogen compounds (NO_y) result in inaccuracies in the estimated NO₂ amount fractions, which limits the applicability of this data to improve atmospheric models and satellite retrievals. With recent advancements in adsorption spectroscopy commercial instruments capable of direct NO₂ measurements are now readily available and the challenges to widespread use of direct NO₂ instruments for regulatory compliance are identified and discussed.