Metrological challenges for measurements of key climatological observables: Oceanic salinity and pH, and atmospheric humidity. Part 1: Overview.

Water in its three ambient phases plays the central thermodynamic role in the terrestrial climate system. Clouds control Earth's radiation balance, atmospheric water vapour is the strongest "greenhouse" gas, and non-equilibrium relative humidity at the air-sea interface drives evaporation and latent heat export from the ocean. On climatic time scales, melting ice caps and regional deviations of the hydrological cycle result in changes of seawater salinity, which in turn may modify the global circulation of the oceans and their ability to store heat and to buffer anthropogenically produced carbon dioxide. In this paper, together with three companion articles, we examine the climatologically relevant quantities ocean salinity, seawater pH and atmospheric relative humidity, noting fundamental deficiencies in the definitions of those key observables, and their lack of secure foundation on the International System of Units, the SI. The metrological histories of those three quantities are reviewed, problems with their current definitions and measurement practices are analysed, and options for future improvements are discussed in conjunction with the recent seawater standard TEOS-10. It is concluded that the International Bureau of Weights and Measures, BIPM, in cooperation with the International Association for the Properties of Water and Steam, IAPWS, along with other international organisations and institutions, can make significant contributions by developing and recommending state-of-the-art solutions for these long standing metrological problems in climatology.

Validation of atmospheric aerosols parallel sampling in a multifold device.

In this work, particulate matter was collected using an active sampling system consisting of a PM10 (<10 µm) inlet coupled to a multifold device containing six channels, connected to a vacuum pump. Each channel was equipped with a filter holder fitted with adequately chosen filters. The system was fixed on a metallic structure, which was placed on the roof of the laboratory building, at the Faculty of Sciences, in Lisbon. Sampling took place under flow-controlled conditions. Aerosols were extracted from the filters with water, in defined conditions, and the water-soluble fraction was quantified by ion chromatography (IC) for the determination of inorganic anions (Cl(-), NO3 (-) and SO4 (2-)). Equivalent sampling through the various channels was validated. Validation was based on the metrological compatibility of the content results for the various filters. Ion masses are metrologically equivalent when their absolute difference is smaller than the respective expanded uncertainty. When this condition is verified, the studied multifold device produces equivalent samples.

Detailed uncertainty budget for major and minor ions in stock combined calibration standards--influence of impurities in chemicals.

A general methodology for a systematic evaluation of the uncertainty was derived for each particular ion in stock combined calibration standards in which concentrations of different ions extend over up to five orders of magnitude resulting in detailed uncertainty budgets with the aim of recognising the major contributions to combined uncertainties. This work confirmed that it is justifiable that the mass fraction of impurities in other chemicals is taken into account when calculating the mass concentration of an ion in combined calibration standard solution similarly to what is already common practice in accounting for the purity of chemical. It was proven that impurities in chemicals which are sources of major ions have significant effect on uncertainty budget of minor ions; already if the major ion exceeds 25 times the minor ion's concentration. For several ions it was confirmed that mass fraction of the impurities was the major source of uncertainty.

Ionic composition of seawaters and derived saline solutions determined by ion chromatography and its relation to other water quality parameters.

Ion chromatography (IC) presents new possibilities for assessing information about environmental samples, namely waters of various compositions, ranging from high-purity water to highly saline ones. Constant proportion between major ions present in seawater, has been assumed in the past, from which the first practical equation relating chlorinity and salinity has been developed, being later substituted by a practical salinity scale, derived from conductivity measurements relative to a standard seawater, according to internationally accepted recommended procedures. Seawaters are characterized by salinity values around 35 while derived saline solutions may present considerable changes in ionic composition, conductivity, hence on salinity. Natural and anthropogenic phenomena may introduce new issues requiring clarification for which qualitative and quantitative information from additional sources is useful, e.g. ionic composition from IC. The different ranges of concentration of major and minor species present in seawater and derived saline solutions are a challenge for the optimization of a practical methodology for composition assessment in two single IC runs, one for anions and another one for cations, which has been attained in this work. Composition of saline solutions determined by IC was critically assessed in terms of anion-cation balance and further related to conductivity and salinity measurements aiming to evaluate the quality/completeness of ion chromatographic analyses performed at preselected conditions and to search for other meaningful relations for efficient recognition/distinction between saline solutions of different types.

Estimation of precision and efficiency mass transfer steps for the determination of pesticides in vegetables aiming at the expression of results with reliable uncertainty.

A 'bottom-up' approach for the expression of results obtained from analytical methods that include analytical steps with recovery inherently different from 100% [mass transfer steps (MTS): extraction, evaporation, clean-up procedures, digestion, etc.] is presented. The estimation of the combination of all MTS uncertainty involves the comparison of the experimental dispersion of replicated analyses of spiked samples with the estimation of the uncertainty obtained for the combination of all uncertainty sources except MTS ones ('incomplete' estimation). The estimation of MTS uncertainty by difference is performed after evaluating the statistical difference between the 'incomplete' estimation and the experimental dispersion (F-test). When the two estimations are statistically equivalent, the MTS uncertainty is considered to be negligible in relation to the other sources budget. The assumption of constancy of MTS performance within the analytical range is tested through single analyses at several concentration levels and is evaluated by the inclusion of the expected values at the intervals resulting from the combination of the MTS uncertainty estimation performed at one concentration level and the 'incomplete' estimation. The developed methodology can also be useful for method optimisation and validation and for the detection of small trends in results. The determination of pesticides in sweet peppers by GC-NPD was used to explore the above concepts.

Effect of different experimental parameters on the potentiometric evaluation of blood electrolytes using K+ as a test cation.

Potentiometric evaluation of ionic concentrations in physiological media has been reported to be significantly affected by the albumin containing matrix. Previous studies have attempted to clarify the origin of different patterns of variation of E versus albumin concentration at a constant 0.01 mol dm-3 KCl, depending on the experimental methodologies. This paper reports on measurements of K+ in albumin (BSA) containing KCl solutions, which have been pursued following different methodologies concerning the sequence of measurements, i.e., starting either from the most concentrated solution (100 g dm-3) (A) or from the most dilute solution (20 g dm-3) (B), and solution preparation, (a) dilution of an initial 100 g dm-3 albumin solution by successive addition of 0.01 mol dm-3 KCl, (b) concentration of an initial 20 g dm-3 albumin solution by addition of solid substance, (c) independent preparation of each albumin solution (20, 40, 60, 80 and 100 g dm-3) or (d) preparation of each albumin solution from direct dilution of a 100 g dm-3 stock solution with 0.01 mol dm-3 KCl. Convenient calculations were made and showed a significant contribution of albumin to the liquid-liquid junction potential. The variation of potential with albumin concentration is smaller for hypertonic than for isotonic bridge solutions, both for the dilution series (A,a and A,d) and for the concentration series (B,c and B,d). When the method for increasing the concentration is performed by addition of a solid substance to an initially diluted albumin (B,b), the slope of the E versus albumin concentration plot is larger for hypertonic than for isotonic reference electrolytes. This latter finding is in agreement with Payne's results when ultrafiltration was used to concentrate a protein solution. These observations are a clear indication that the method of preparation of concentrated protein solutions may significantly affect the results.