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We report 3 years of data from one meteorological and three smaller stations in University Valley, a high-elevation (1677 m) site in the Dry Valleys of Antarctica with extensive dry permafrost. Mean air temperature was -23.4°C. Summer air temperatures were virtually always < 0°C and were consistent with the altitude lapse rate and empirical relationships between summer temperature, distance from the coast and elevation. The measured frost point (-22.5°C) at the 42 cm deep ice table is equal to the surface frost point and above the atmospheric frost point (-29.6°C), providing direct evidence that surface conditions control ground ice depth. Observed peak surface soil temperatures reach 6°C for ice-cemented ground > 15 cm deep but stay < 0°C when it is shallower. We develop an energy balance model tuned to this rocky and dry environment. We find that differences in peak soil surface temperatures are primarily due to the higher thermal diffusivity of ice-cemented ground compared to dry soil. Sensitivity studies show that expected natural variability is insufficient for melt to form and significant excursions from current conditions are required. The site's ice table meets the criteria for a Special Region on Mars, with 30% of the year > -18°C and water activity > 0.6. [ABSTRACT FROM AUTHOR]

Dry permafrost - ground with temperature always below 0°C and containing negligible ice - overlying ice-cemented ground has been reported in the Dry Valleys of Antarctica and on Mars. Here we report on a new site (79°49.213'S, 83°18.860'W, 718 m elevation) located on the side of Mount Dolence in Ellsworth Land, Antarctica. Year-round temperature and humidity measurements indicate that dry permafrost is present between depths of 13.5 and 49.0 cm - the location of ice-cemented ground. The mean annual frost point of the ice-cemented ground is -17.0 ± 0.2°C and the mean annual frost point of the atmosphere is -22.7 ± 1°C. The corresponding mean annual temperatures are -19.2°C and -20.3°C. Neither the temperature of the ice-cemented ground nor the air rise above freezing. Both the dry permafrost and the ice table may be habitable. In the dry soil at 3 cm depth there are 80 hours in the summer when temperature exceeds -5°C and water activity exceeds 0.8. At the ice table, temperature exceeds -10°C and water activity exceeds 0.8 for 35 hours in the year. The ice table and the dry permafrost above it would be considered a 'Special Region' on Mars. Further microbial investigation of this site is indicated. [ABSTRACT FROM AUTHOR]

The aim of this paper is to describe the evaluation process of the performance of the low-range saturator (LRS), when exposed to two different thermal environments. The examined saturator was designed, built, and tested at MIKES (Centre for Metrology and Accreditation, Finland), and then transported to the Laboratory for Process Measurement (LPM) in Croatia, where it was implemented in a new dew-point calibration system. The saturator works on a single-pressure-single-pass generation principle in the dew/frost-point temperature range between $$-70\,^{\circ }\hbox {C}$$ and $$+5\,^{\circ }\hbox {C}$$ . The purpose of the various tests performed at MIKES was to examine the efficiency and non-ideality of the saturator. As a test bath facility in Croatia differs from the one used in Finland, the same tests were repeated at LPM, and the effects of different thermal conditions on saturator performance were examined. Thermometers, pressure gauges, an air preparation system, and water for filling the saturator at LPM were also different than those used at MIKES. Results obtained by both laboratories indicate that the efficiency of the examined saturator was not affected either by the thermal conditions under which it was tested or by equipment used for the tests. Both laboratories concluded that LRS is efficient enough for a primary realization of the dew/frost-point temperature scale in the range from $$-70\,^{\circ }\hbox {C}$$ to $$+5\,^{\circ }\hbox {C}$$ , with flow rates between $$1\hbox { L}{\cdot }\hbox {min}^{-1}$$ and $$2.5\hbox { L}{\cdot }\hbox {min}^{-1}$$ . It is also shown that a considerable difference of the pre-saturator efficiency, indicated by two laboratories, did not have influence to the overall performance of the saturator. The results of the research are presented in graphical and tabular forms. This paper also gives a brief description of the design and operation principle of the investigated low-range saturator. [ABSTRACT FROM AUTHOR]

Abstract: An investigation of hygrometers for monitoring of water vapour (moisture) in natural gas has been performed, with respect to response on ethylene glycol co-exposure. The tested hygrometers are based on: 1. capacitor sensor, 2. quartz crystal microbalance (QCM), 3. fibre-optic sensor and 4. conversion of water to ethyne, quantified by a gas chromatograph (CaC2-GC). The moisture concentration level in the test gas was 50 μmol/mol during the experiments, corresponding to a frost point of approximately −48 °C (atmospheric pressure). The experiments were performed in the laboratory, using nitrogen as matrix gas. The QCM hygrometer responded with a downward drift of the frost point readings in the presence of traces of ethylene glycol (0.25 μmol/mol and 0.66 μmol/mol, respectively). The drift increased initially when the ethylene glycol concentration increased, and the frost point readings from the QCM hygrometer decreased close to 5 °C during a total of 20 days of ethylene glycol exposure. The QCM hygrometer seemed to recover slowly from the ethylene glycol exposure, indicated by a decreasing upward drift as soon as the ethylene glycol exposure ended. Both tested capacitor hygrometers responded significantly to ethylene glycol exposure. The responses were not uniform, though, with one performing considerably better than the other one. The experiments also demonstrated the insufficiency of chilled mirror techniques for interpreting water frost points or water dew points, with subsequent moisture concentration calculation, in the presence of ethylene glycol, even at trace amounts. This made the chilled mirror technique totally unsuitable for reference measurements after the introduction of ethylene glycol to the test gas. The fibre-optic sensor hygrometer and the CaC2-GC hygrometer showed minor response for ethylene glycol. In general the results from this work demonstrate the need for careful evaluation of individual moisture monitoring applications, before choosing a hygrometer. A well-considered strategy for quality control of the moisture monitoring, regardless of the chosen hygrometer, is of utmost importance to establish a moisture monitoring system with high accuracy. [Copyright &y& Elsevier]

A precision trace humidity calibration system using permeation tubes has been implemented, and measurements have been performed in the range between 100 nmol/mol (100 ppb) and 245 nmol/mol (245 ppb) with flow rates between $${1\,{\rm L}{\cdot}{\min}^{-1}}$$ and $${5\, {\rm L}{\cdot} {min}^{-1}}$$ . The preliminary results of the commissioning of the permeation tube generator and its use in the comparison of humidity analyzers based on different measurement principles are presented and discussed. The work reported comprises the first stage in establishing the detailed design and operational characteristics of the future standard moisture generation to extend the range currently covered by Spanish national humidity standards. A precision optical dew-point hygrometer, a quartz crystal microbalance moisture analyzer, and a cavity ringdown spectrometer have been compared, and the response times and repeatability have been investigated. The design criteria and the characterization of the system as well as the estimation of measurement uncertainty in each case are presented. [ABSTRACT FROM AUTHOR]

Recent studies have shed new light on humidity conditions in the polar atmospheric boundary layer, and cast doubt on the reliability of humidity measurements above the frost point humidity. These issues are addressed herein by considering the processes that affect humidity and its measurement in cold climate conditions and by analyzing observations from two sites, at which the relative humidity is frequently above 100% at sub-freezing temperatures, as shown by repeatedly observed in-cloud icing events. Humidity measurements were made at these two sites by the commonly used Vaisala HMP35 probe and HMP233 capacitance probes respectively and simultaneously by the same manufacturer’s HMP243 probe that determines the frost point by a heated capacitance sensor. The results confirm that the relative humidity is frequently well above the frost point, both due to radiative cooling and to the advection of moist air, and that the conventional humidity measurements are unable to detect these events. Furthermore, after such events, the iced sensors show too high a humidity. The false values occur due to ice growth on the probe and cannot be corrected by any algorithm. Our results indicate that these problems, inherent to conventional humidity measurements in cold and humid environments, are avoided by the use of HMP243, which has a heated humidity probe. [ABSTRACT FROM AUTHOR]

The water content of gas is of importance in a wide variety of areas such as oil and gas, carbon capture and storage, medical, nuclear, food and hydrogen cells. In cases where pressurised gas is being used or transported in pipelines (i.e. natural gas, carbon dioxide, compressed air....) changes in temperature or pressure may result in water condensing. The condensed water may cause a number of issues such as corrosion, ice and hydrate formation. In order to avoid water condensing the gas needs to be dried to a level where condensation will not occur at any temperature/pressure conditions encountered. There are a wide variety of methods and equipment available for making water content measurements in laboratory or industrial processes. The available devices vary in terms of different parameters such as accuracy, long-term stability, sensitivity to contaminants, response time, pressure rating, initial and running costs. This paper introduces a new method that can potentially be incorporated into equipment for use in both laboratory and field applications for accurate dew/frost point measurements at a wide range of pressures. Initial measurements have been made for nitrogen, methane and natural gas and the results have been compared with literature data and model predictions. [ABSTRACT FROM AUTHOR]

Many applications dealing with carbon dioxide are limited because of carbon dioxide frosting. Therefore, it has been important to accurately predict the temperature where carbon dioxide solidifies. In this work, using solid – vapor (SV) equilibria, the frost points of binary and ternary model systems resembling natural gases – that are, methane + carbon dioxide, nitrogen + methane + carbon dioxide and methane + ethane + carbon dioxide are predicted by the predictive Peng-Robinson 1978 (PPR78), Redlich-Kwong-Soave (RKS), Nasrifar-Bolland (NB) equations of state and a solid fugacity relation. The equations of state are used to describe the vapor phase in SV equilibria. Accordingly, the equations of state are coupled with a group-contribution temperature-dependent binary interaction parameter that was previously developed from vapor – liquid (VL) equilibria. The solid fugacity relation was developed in this work for describing solid carbon dioxide. The solid fugacity relation expands around the triple point temperature of carbon dioxide. It is explicit in temperature and pressure and needs triple point temperature and sublimation enthalpy of carbon dioxide as input parameters. The model is fully predictive and does not require any adjustable parameter. When the NB equation of state with the solid fugacity relation was applied to natural gas model systems (NGMS), the agreement with experiments was found satisfactory. The NGMS contained 0.1%–54.2% carbon dioxide, temperature and pressure ranged from 140 K to 216 K and 100 kPa–3500 kPa, respectively. The effects of nitrogen and ethane on the frost point were also evaluated and the model accuracy was found adequate. Average absolute deviation (AAD) in predicting 291 experimental frost points for binary and ternary mixtures containing carbon dioxide was found to be 1.58 K. • A fugacity relation to describe solid carbon dioxide was developed. • The fugacity relation is explicit in temperature and pressure. • Predictive equations of state were used to describe the vapor phase. • No adjustable parameter was required. • The frost points of model systems from low to the triple point temperature were predicted satisfactorily. [ABSTRACT FROM AUTHOR]

A Regional Metrology Organization (RMO) Key Comparison of dew/frost point temperatures over the range -30 °C TO +20 °C was carried out by the National Institute of Standards and Technology (NIST, USA) and the Laboratorio Costarricense de Metrología (LACOMET, Costa Rica), between February 2015 and August 2015. The results of this comparison are reported here, along with descriptions of the humidity laboratory standards for NIST and LACOMET and the uncertainty budget for these standards. This report also describes the protocol for the comparison and presents the data acquired. The results are analyzed, determining the degree of equivalence between the dew/frost-point standards of NIST and LACOMET.

A Regional Metrology Organization (RMO) Key Comparison of dew/frost point temperatures was carried out by the National Institute of Standards and Technology (NIST, USA) and the National Research Council (NRC, Canada) between December 2014 and April, 2015. The results of this comparison are reported here, along with descriptions of the humidity laboratory standards for NIST and NRC and the uncertainty budget for these standards. This report also describes the protocol for the comparison and presents the data acquired. The results are analyzed, determining degree of equivalence between the dew/frost-point standards of NIST and NRC.