Trends in Atmospheric Trace Gas Measurement Instruments with Membrane-based Gas Diffusion Scrubbers

Abstract

A diffusion scrubber (DS) is an excellent tool for gas analysis, and there are many types of DS devices, varying both in structure and construction. In this paper, recent work on atmospheric trace gas measurements by means of DS devices are reviewed. Theoretical considerations on representative DSs are summarized first. Then, the characteristics of the key material, a gas-diffusion membrane, are discussed, and recent improvements and novel scrubbers for highly effective collection are outlined. A chromatograph is a suitable tool for the multi-gas analysis of collected species. On the other hand, solid-state fluorescence/absorbance detectors have been developed for the continuous measurement of target gases. The methods based on DS collection and subsequent detection have high sensitivities, and the detection limits can be in the low-pptv levels. Accordingly, they are capable of measuring background levels, and detecting very low levels of contaminants in a cleanroom. Miniaturized advanced DS units, perhaps the next generation of DS devices, are introduced at the end of this review. DS systems have contributed significantly to our knowledge of the atmospheric dynamics and atmospheric chemistry.

Gas collection efficiency of annular denuders: A spreadsheet-based calculator

“…Equating this axial distance to the length of the denuder, the fractional penetration f p is given by dividing this concentration value by the inlet concentration. In the following, we use available results for the thermal problem to predict the performance of three types of annular denuders: (A) those for which the outer wall is a sink, and the inner wall is inert (an inert rod-filled denuder, as it were, a geometry that has not been much used), (B) those for which the inner wall is a sink, and the outer wall is inert (this is the case for a variety of membrane-based diffusion scrubbers [2,3]), and (C) those for which both walls are sinks, as in common annular denuders. We also consider the limiting case that the inner radius shrinks to zero, and the annulus becomes a single tube.…”

“…The use of diffusion denuders, and their membrane-based analogs, diffusion scrubbers, have been extensively reviewed [1][2][3][4][5][6]. In its simplest form, a denuder is a tube with its inner walls bearing some material that acts as a sink for the analyte gas of interest.…”

Micro gas analyzers for environmental and medical applications

“…In contrast to the sorbent-coated diffusion denuders, this device can be used continuously and repeatedly. Among the membrane-based diffusion scrubbers, an annular arrangement is preferred for miniature systems [14]. The solution volume held in a small membrane tube is only ∼100 L. Annular diffusion scrubbers have been coupled to flow analyzers and applied to real atmospheric analyses for peroxides (H 2 O 2 , CH 3 HO 2 ) [15] and HCHO [16,17].…”

Gas sensors based on membrane diffusion for environmental monitoring

“…The membrane plays a vital role in sensing analytes in the environment: firstly, the membrane introduces a selective passage for analyte molecules through the membrane and regulates the diffusion kinetics; secondly, it remains the sensing component within the sensor body and protects the transducers from possible contaminants. Therefore, membrane-based sensors can selectively recognize gas analytes and it is independent of the matrix of the sample, which is superior to other sensors without membrane that is greatly affected by sample matrix, such as some polymerabsorption chemiresistors and some mass gas sensors [6][7][8].…”