Bilateral comparison of primary reference materials (PRMs) containing methanol, ethanol and acetone in nitrogen

Abstract

A range of oxygenated volatile organic compounds (OVOCs) are present in the atmosphere as a result of direct emissions and as products of atmospheric oxidation. Long-term measurements are important to understand changes to these emission sources and atmospheric oxidation processes. Accurate and stable traceable gaseous primary reference materials are needed to underpin rigorous quality assurance and quality control at monitoring stations such as those organised by the World Meteorological Organization Global Atmosphere Watch (WMO-GAW) programme. The development of a capability for providing traceable primary reference materials (PRMs) of OVOCs is of paramount importance due to the increasing prevalence of these compounds in the urban atmosphere and also because there is currently no Central Calibration Laboratory (CCL) for these components within the WMO-GAW programme. This EURAMET bilateral comparison demonstrates the measurement compatibility (≤ 3%) for three OVOCs (methanol, ethanol and acetone) at nominally 5 µmol mol−1 between two National Metrology Institutes: the National Physical Laboratory (NPL), UK and the Van Swinden Laboratorium (VSL), the Netherlands. The comparison shows that a gravimetric method for value assignment is applicable to acetone but that a more complicated procedure must be employed to value assign methanol and ethanol due to corrections for adsorption effects, which can be as large as 10 % of the nominal value. This work demonstrates the importance of making appropriate corrections to ensure the accuracy of these reference materials. NPL and VSL used different approaches to make these corrections providing confidence and independent verification. This work supports new calibration and measurement capabilities for methanol, ethanol and acetone in the range of 1 μmol mol−1 –10 μmol mol−1 with expanded uncertainties of 6.9 % (3 %), 7.3 % (3 %) and 1.7 % (2 %) for NPL (VSL), respectively, to be realized in the key comparison database and supports the development of the required traceability infrastructure to underpin long-term global measurements of these OVOCs.

Development of an SI-traceable transmission curve reference material to improve comparability of proton transfer reaction mass spectrometry measurements

“…The second group is acetone, DMS, MVK and PFTBA where the spread in the validation data is within 5 % and these are relatively new components where capabilities were developed more recently. Recognising the challenges in preparing PRMs containing siloxanes as a result of their low vapour pressures and observing the recent improvements in preparation since 2019, the D4-siloxane and D5-siloxanes can also be categorised as group 2 after excluding the earliest parent preparations used for A574 and A578 in 2017, which are inconsistent with more recent work as part of the EURAMET 1305 Siloxanes comparison (Van Der Veen et al, 2022). The final group is comprised of D3-siloxane and 1,2,4-TCB where the spread in validation data is within 10 % and these compounds represent those which the most challenging to prepare as a result of their low vapour pressures.…”

“…Stability of all six NPL PRMs were assessed by tracking the ratios of the FID responses of each component relative to an internal reference that was present in every mixture and which is known to be stable (Rhoderick, 2010;Rhoderick and Lin, 2013;Worton et al, 2022). Propane was originally included as an internal tracer to monitor stability but as the PTR-MS in H3O + mode cannot detect this compound it was replaced by benzene.…”

A new look at the sorption kinetics in reference gas standards

“…As a result, gravimetrically prepared methanol reference gas standards suffer from strong adsorption losses (e.g. about −9% at 5 µmol mol −1 for the cylinder passivation under test in [23]) making the use of adsorption corrections necessary. There exists a need for lower amount fraction standards as typical amount fractions in the atmosphere are in the sub nmol/mol and low nmol/mol range [19].…”

“…(1) By comparison against other gas mixture preparation methods (e.g. dynamic methods like diffusion cells or permeation) [23]. Such dynamic preparation methods can directly provide an absolute quantification of the adsorption loss.…”