Traceable PM2.5 and PM10 Calibration of Low-Cost Sensors with Ambient-like Aerosols Generated in the Laboratory

This work builds upon previous efforts at calibrating PM (particulate matter) monitors with ambient-like aerosols produced in the laboratory under well-controlled environmental conditions at the facility known as PALMA (Production of Ambient-like Model Aerosols). In this study, the sampling system of PALMA was equipped with commercial PM2.5 and PM10 impactors, designed according to the EN 12341:2014 standard, to select different aerosol size fractions for reference gravimetric measurements. Moreover, a metallic frame was mounted around the PM impactor to accommodate up to eight low-cost PM sensors. This sampling unit was placed at the bottom of the 2-meter-long aerosol homogenizer, right above the filter holder for the reference gravimetric measurements. As proof of principle, we used the upgraded PALMA facility to calibrate the new AirVisual Outdoor (IQAir, Goldach, Switzerland) and the SDS011 (InovaFitness, Jinan, China) low-cost PM sensors in a traceable manner against the reference gravimetric method according to the EN 12341 standard. This is the first time that PM2.5 and PM10 calibrations of low-cost sensors have been successfully carried out with complex ambient-like aerosols consisting of soot, inorganic species, secondary organic matter, and dust particles under controlled temperature and relative humidity.

DETERMINATION OF THE VERTICAL GRADIENT OF GRAVITY FROM GRAVITY ANOMALIES

In connection with the need to use the vertical gradient in the processing of the results of gravimetric measurements and their interpretation when solving problems of geology, geophysics, geodesy, geodynamics and navigation, in addition to the urgent problems of improvement, socalled indirect methods of measuring the vertical gradient, there is an equally urgent task of developing methods for determining the vertical gradient of gravity, using dependencies between different physical fields. The article presents the development and study of a method for determining the vertical gradient from gravity anomalies using the relationship between gravity anomalies and altitude based on field data obtained in the area of the Tashtagol field on Mount Boulanger in 2019 and 2020.

Investigation of the repeatability of a cleaning method for silicon spheres by gravimetric measurements

After a short description of the metrological relevance of silicon spheres and the applied cleaning method, mass measurements of silicon spheres in vacuum and the evaluation of the results are outlined. The results show that the mass of silicon spheres in vacuum stabilises in the microgram range within two to three days after cleaning and that the repeatability of the applied cleaning method can be characterised by a standard deviation in the order of two micrograms.

Gravity field modelling for the Hannover 10 m atom interferometer

Absolute gravimeters are used in geodesy, geophysics and physics for a wide spectrum of applications. Stable gravimetric measurements over timescales from several days to decades are required to provide relevant insight into geophysical processes. Users of absolute gravimeters participate in comparisons with a metrological reference in order to monitor the temporal stability of the instruments and determine the bias to that reference. However, since no measurement standard of higher-order accuracy currently exists, users of absolute gravimeters participate in key comparisons led by the International Committee for Weights and Measures. These comparisons provide the reference values of highest accuracy compared to the calibration against a single gravimeter operated at a metrological institute. The construction of stationary, large-scale atom interferometers paves the way for a new measurement standard in absolute gravimetry used as a reference with a potential stability up to $$1\,\hbox {nm}{/}{\hbox {s}^{2}}$$ 1 nm / s 2 at 1 s integration time. At the Leibniz University Hannover, we are currently building such a very long baseline atom interferometer with a 10-m-long interaction zone. The knowledge of local gravity and its gradient along and around the baseline is required to establish the instrument’s uncertainty budget and enable transfers of gravimetric measurements to nearby devices for comparison and calibration purposes. We therefore established a control network for relative gravimeters and repeatedly measured its connections during the construction of the atom interferometer. We additionally developed a 3D model of the host building to investigate the self-attraction effect and studied the impact of mass changes due to groundwater hydrology on the gravity field around the reference instrument. The gravitational effect from the building 3D model is in excellent agreement with the latest gravimetric measurement campaign which opens the possibility to transfer gravity values with an uncertainty below the $${10}\,\hbox {nm}{/}{\hbox {s}^{2}}$$ 10 nm / s 2 level.

Analysis of the Dynamic Height Distribution at the Estuary of the Odra River Based on Gravimetric Measurements Acquired with the Use of a Light Survey Boat—A Case Study

This article presents possible applications of a dynamic gravity meter (MGS-6, Micro-g LaCoste) for determining the dynamic height along the Odra River, in northwest Poland. The gravity measurement campaign described in this article was conducted on a small, hybrid-powered survey vessel (overall length: 9.5 m). We discuss a method for processing the results of gravimetric measurements performed on a mobile platform affected by strong external disturbances. Because measurement noise in most cases consists of signals caused by non-ideal observation conditions, careful attempts were made to analyze and eliminate the noise. Two different data processing strategies were implemented, one for a 20 Hz gravity data stream and another for a 1 Hz data stream. A comparison of the achieved results is presented. A height reference level, consistent for the entire estuary, is critical for the construction of a safe waterway system, including 3D navigation with the dynamic estimation of under-keel clearance on the Odra and other Polish rivers. The campaign was conducted in an area where the accuracy of measurements (levelling and gravimetric) is of key importance for shipping safety. The shores in the presented area of interest are swampy, so watercraft-based measurements are preferred. The method described in the article can be successfully applied to measurements in all near-zero-depth areas.

Vibrational Spectroscopic Monitoring of the Gelation Transition in Nafion Ionomer Dispersions

Infrared and Raman spectroscopy techniques were applied to investigate the drying and aggregation behavior of Nafion ionomer particles dispersed in aqueous solution. Gravimetric measurements aided the identification of gel-phase development within a series of time-resolved spectra that tracked transformations of a dispersion sample during solvent evaporation. A spectral band characteristic of ionomer sidechain end group vibration provided a quantitative probe of the dispersion-to-gel change. For sets of attenuated total reflection Fourier transform infrared (ATR FT-IR) spectra, adherence to Beer's law was attributed to the relatively constant refractive index in the frequency region of hydrated –[Formula: see text] group vibrations as fluorocarbon-rich ionomer regions aggregate in forming the structural framework of membranes and thin films. Although vibrational bands associated with ionomer backbone CF2 stretching vibrations were affected by distortion characteristic of wavelength-dependent refractive index change within a sample, the onset of band distortion signaled gel formation and coincided with ionomer mass % values just below the critical gelation point for Nafion aqueous dispersions. Similar temporal behavior was observed in confocal Raman microscopy experiments that monitored the formation of a thin ionomer film from an individual dispersion droplet. For the ATR FT-IR spectroscopy and confocal Raman microscopy techniques, intensity in the water H–O–H bending vibrational band dropped sharply at the ionomer critical gelation point and displayed a time dependence consistent with changes in water content derived from gravimetric measurements. The reported studies lay groundwork for examining the impact of dispersing solvents and above-ambient temperatures on fluorinated ionomer transformations that influence structural properties of dispersion-cast membranes and thin films.

Process Control of Drug Product Continuous Manufacturing Operations—a Study in Operational Simplification and Continuous Improvement

Purpose The purpose of this manuscript is to demonstrate that implementation of gravimetric measurements provides the same assurance of product quality and process control as spectroscopic measurements (1) for control of drug content in a fixed-dose combination (FDC) tablet and (2) for identification of non-conforming material. Methods A wet granulation continuous tableting line was used to make the FDC drug product batches. Comparative data was generated for ten batches using near-infrared (NIR) spectroscopy for core tablets, and gravimetric in-process control measurements (IPCs) applied to the ratio control of intra- and extra-granular blend (IG and EG). HPLC reference data were collected to further demonstrate uniformity at each stage of the production process, including IG, final blend, and core tablets. All possible sources of variation not directly detectable by the gravimetric measurements were considered and quantified. Results The two IPC measurement techniques showed excellent agreement where both were within 2% of the target drug concentrations and within 2% of each other for the ten comparative batches. The NIR was more sensitive to material and process variations than the gravimetric IPCs; thus, it was more variable within and across batches. Gravimetric IPCs were demonstrated as an effective replacement for spectroscopic measurements for continuous tableting operations, capable of ensuring on target manufacturing and detection of non-conforming material. Conclusions As pharmaceutical companies continue to push toward operational simplicity and sustainable manufacturing processes, soft-sensor and gravimetric controls as alternatives to their spectroscopic counterparts will be applied more broadly for process monitoring and control.