VSL develops gas standards for portable emission measurement system (PEMS)

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VSL develops gas standards for portable emission measurement system (PEMS)

European legislation sets strict limits on nitrogen oxides (NOx) and particulate matter (PN) emitted from vehicle exhaust, as both are a major source of air pollution and are hazardous to human health. Emission tests with real car journeys have recently been introduced in the EU to provide a more realistic picture of these vehicle emissions. Such tests are performed with Portable Emissions Measurement Systems (PEMS) that allow real-world testing of emissions, but a full metrological characterization of these systems is currently lacking. VSL is a partner of the MetroPEMS project ((2020-2023), https://lnkd.in/exPVpDmc), which addresses the need for PEMS calibration standards and guidelines.

VSL develops reliable gas standards for testing and calibration of PEMS instruments. Nitrogen dioxide (NO2) at high mole fractions (> 500 µmol/mol) is one of the most important components in such gas standards. Gas standards with a low NO2 mole fraction (< 10 µmol/mol) pose an analytical problem due to the unavoidable presence of nitric acid (HNO3), as recently shown in an international comparison (https://lnkd.in/dYGbvhBB), but high NO2 mole fractions, as relevant for portable emission measurement systems, are even more challenging. This is due to the formation of N2O4, the NO2 dimer.

VSL has prepared several NO2 gas standards in the range of 500-2500 µmol/mol, including binary gas standards of NO2 in synthetic air and multi-component mixtures containing nitric oxide, carbon monoxide, carbon dioxide and NO2, in nitrogen.

The stability of the developed gas standards is currently being checked with various analytical techniques, including VSL’s new FTIR spectrometer facility, which allows the accurate quantification of both nitric acid and the NO2 dimer. The results of the first 6 months of stability testing are promising and this research will be continued to obtain 1 year stability data. The graph shows the VSL experimental data for the quantification of N2O4 in the binary NO2 gas standards and a simulation based on an equilibrium model for comparison. The results of this developmental study will be published.