Nitrogen dioxide

02/12/2019

Nitrogen dioxide (NO2) is the air pollutant which has the greatest impact on human health and wellbeing. A major source of NO2 in cities comes from automotive exhausts. These exhaust gases contain NOx, which refers to mainly NO and NO2. The latter is in equilibrium with its dimer N2O4. A gas mixture containing NOx can be analysed using a non-specific NOx analyser such as a chemiluminescence-based analyser with converter. For the specific analysis of NO2 in a NOx-containing gas mixture a measurement technique like Cavity Attenuated Phase Shift (CAPS) can be used. Driven among others by the US Environmental Protection Agency (EPA) acceptance of direct-reading NO2 analysers as federal equivalent method for NO2, a need has emerged for the accurate specification of the amount-of-substance fractions of NO2 instead of NOx in analytical reference standards. 

To address this need, VSL has worked on fully characterizing the various NOx species in NO2 Primary Reference materials (PRM) to avoid improper results. Minimization and accurate quantification of impurities in NOx reference standards such as water, other nitrogen oxide compounds (e.g., nitric acid) and N2O4 are paramount, because their presence increases uncertainty and decreases long-term stability of the certified NO2 fraction. 
Furthermore, VSL is pursuing efforts to further reduce the uncertainty of their low fraction NO2 PRMs (≤ 10 x 10-6 mol/mol) and to improve their stability. Studies on different cylinder types and treatments to obtain (beyond) the state-of-the-art NO2 gas mixtures are taking place. 

During Pittcon 2019 (March 17 – 21, 2019, Pennsylvania Convention Center, Philadelphia, Pennsylvania, USA) our VSL expert will present the latest research results regarding NOx gaseous reference materials (9:10 - 9:30 am on Monday 18 March 2019, Abstract number 320-3; Location 121C, Session 320 Specialty Gases). 

Pittcon 2019 will be a major networking opportunity. Please use this opportunity and get into contact with VSL! Next to our NOx gaseous reference materials, you can get information about all our other services at our booth in the exhibition area (number 2232).