Dilution and permeation standards for the generation of NO, NO₂and SO₂calibration gas mixtures

Abstract

The evaluation results of the metrological performance of a dilution and a permeation standard for generating SI-traceable calibration gas mixtures of NO, SO2 and NO2 for ambient air measurements are presented. The composition of the in situ produced reference gas mixtures is calculated from the instantaneous values of the input quantities of the generating standards. In a measurement comparison, the calibration and measurement capabilities of five laboratories were evaluated for the three analytes at limiting amount of substance fractions in ambient air between 20 and 150 nmol mol−1. For the upper generated reference values the target relative uncertainties of ⩽2% (for NO and SO2) and ⩽3% (for NO2) for evaluating the laboratory results were fulfilled in 12 out of 13 cases. For the analytical results seven out of nine laboratories met the criteria for the upper values for NO and NO2, for SO2 it was one out of four. From the negative degrees of equivalence of all NO2 comparison results it was supposed that the permeation rate of NO2 through the FEP polymer membrane of the permeator was different in air and N2. Subsequent precision permeation measurements with various carrier gases revealed that the permeation rate of NO2 was ≈0.8% lower in synthetic air compared to N2. With the corrected NO2 reference values for air the degrees of equivalence of the laboratory results were improved and closer to be symmetrically distributed.

Measurement report: Characterization of uncertainties in fluxes and fuel sulfur content from ship emissions in the Baltic Sea

“…The laboratory maintains the traceability of the calibration to the SI units, and it is accredited according to ISO 17025:2005 for all measured gas compounds except CO 2 . The dynamic dilution method by accurate gas sources was used for the calibration (Haerri et al, 2017). The calibration concentrations were selected to cover the expected measurement ranges for each of the gas components.…”

Dynamic-gravimetric preparation of metrologically traceable primary calibration standards for halogenated greenhouse gases

“…Reference gas generation by applying the permeation method combined with dynamic dilution is an established, standardised technique, particularly for reactive gases (e.g., O'Keeffe and Ortman, 1966;Scaringelli et al, 1970;Brewer et al, 2011;Flores et al, 2012;Haerri et al, 2017). It is routinely used at METAS following a procedure in compliance with international standards (ISO 6145-10, 2002;ISO 6145-7, 2009).…”

“…The permeation rate is exponentially depending on temperature; secondary influences are carrier gas composition and pressure (Lucero, 1971;Moosbach and Hartkamp, 1993;Jost, 2004;Brito and Zahn, 2011;Haerri et al, 2017). For mass loss determination, each permeator is placed individually in our magnetic suspension balance 'Violetta' (hereafter MSB-Violetta, 5 model FLUIDIFF MP, installed in 2014, Rubotherm, Germany, Fig.…”

Effect of external pressures in dynamic gas mixers

“…The metered components are mixed in a chamber to form a gas mixture of a specified concentration [17].…”