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Under the EU Air Quality Directive (AQD) 2008/50/EC member states are required to undertake routine monitoring of PM 2.5 composition at background stations. The AQD states for PM 2.5 speciation this should include at least: nitrate NO 3 - , sulfate SO 4 2 - , chloride (Cl - ), ammonium (NH4 + ), sodium (Na + ), potassium (K + ), magnesium (Mg 2+ ), calcium (Ca 2+ ), elemental carbon (EC) and organic carbon (OC). Until 2017, it was the responsibility of each country to determine the methodology used to report the composition for the inorganic components of PM 2.5 . In August 2017 a European standard method of measurement of PM 2.5 inorganic chemical components ( NO 3 - , SO 4 2 - , Cl - , NH 4 + , Na + , K + , Mg 2+ , Ca 2+ ) as deposited on filters (EN16913:2017) was published. From August 2019 this then became the European standard method. This filter method is labour-intensive and provides limited time resolution and is prone to losses of volatile compounds. There is therefore increasing interest in the use of alternative automated methods. For example, the UK reports hourly PM 2.5 chemical composition using the Monitor for AeRosols and Gases in Ambient air (MARGA, Metrohm, NL). This study is a pre-assessment review of available data to demonstrate if or to what extent equivalence is possible using either the MARGA or other available automatic methods, including the Aerosol Chemical Speciation Monitor (ACSM, Aerodyne Research Inc. US) and the Ambient Ion Monitor (AIM, URG, US). To demonstrate equivalence three objectives were to be met. The first two objectives focused on data capture and were met by all three instruments. The third objective was to have less than a 50% expanded uncertainty compared to the reference method for each species. Analysis of this objective was carried out using existing paired datasets available from different regions around the world. It was found that the MARGA (2006-2019 model) had the potential to demonstrate equivalence for all species in the standard, though it was only through a combination of case studies that it passed uncertainty criteria. The ACSM has the potential to demonstrate equivalence for NH 4 + , SO 4 2 - and in some conditions NO 3 - , but did not for Cl - due to its inability to quantify refractory aerosol such as sea salt. The AIM has the potential for NH 4 + , NO 3 - , SO 4 2 - , Cl - and Mg 2+ . Future investigations are required to determine if the AIM could be optimised to meet the expanded uncertainty criterion for Na + , K + and Ca 2+ . The recommendation is that a second stage to demonstrate equivalence is required which would include both laboratory and field studies of the three candidate methods and any other technologies identified with the potential to report the required species., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. more...

We have shown that the amount fraction of carbon dioxide in a nitrogen or synthetic air matrix stored in cylinders increases as the pressure of the gas mixture reduces, while the amount fraction of methane remains unchanged. Our measurements show the initial amount fraction of carbon dioxide to be lower than the gravimetric value after preparation, which we attribute to the adsorption of a proportion of the molecules to active sites on the internal surface of the cylinder and the valve. As the mixture is consumed, the pressure in the cylinder reduces and the amount fraction of the component is observed to increase. The effect is less pronounced in the presence of water vapor. More dramatic effects have been observed for hydrogen chloride. These findings have significant implications for the preparation of high accuracy gaseous reference materials with unprecedented uncertainties which underpin a broad range of requirements, in particular atmospheric monitoring of high impact greenhouse gases. more...

Deficiencies with the current European reference method for the analysis using inductively couple plasma-mass spectrometry of metals in samples from stationary emissions sources are presented based on experimental data obtained from real samples. The effect of these deficiencies on the quality and accuracy of data is highlighted with biases of up to 40% being observed in real samples. Suggestions to improve the performance of the standard method are presented. In particular, the beneficial effect of using a drift correction procedure to account for the decrease in instrument sensitivity observed during an analytical measurement series is demonstrated. It is shown that this corrective procedure results in substantial improvements to the accuracy of data produced. more...