Analysis of Atmospheric Radiosulfur at Natural Abundance by a New-Type Liquid Scintillation Counter Equipped with Guard Compensation Technology

Abstract

High-sensitivity measurements of radiosulfur (cosmogenic 35S; half-life: 87.4 days) at natural abundance using ultra-low-level liquid scintillation counter (LSC) methods have been developed and optimized in the last decade, providing new details in space, atmospheric, and hydrological sciences. These LSC methods heavily rely on instruments conventionally equipped with 650 kg lead blocks that passively shield cosmic and environmental background radiation, but this type of instrument is not commercially available anymore, hindering further applications of 35S. To solve this problem, we extended the methods to a new-type LSC equipped with new mathematics-based active shielding techniques (Guard Compensation Technology; GCT). The counting efficiency of the new-type LSC for low-35S activity samples (e.g., natural samples) is low and highly variable because a portion of true signals from 35S decay events was undesirably removed by GCT. We therefore developed a new data processing protocol to determine 35S activities accurately and precisely in the range between ∼1 and ∼13 disintegrations per minute, and its validity was tested by working standards with known 35S activities. As an application example, we measured concentrations of 35S in sulfate aerosols collected in Guangzhou, a megacity in subtropical South China. The obtained values are within the range of previously reported data from various mid-latitude sampling sites. Based on these results, we conclude that our protocol allows the continuing utility of 35S measurements using a new-type LSC for a deeper understanding of the atmospheric sulfur cycle and its influences on the environment, climate, and public health.

Toward the Origins of Quadruple Sulfur Isotope Anomalies in Modern Sulfate: A Multitracer Approach and Implications for Paleo- and Planetary Atmospheres

“…Blank filter papers were also subjected to the same extraction procedure to determine background levels of water-soluble ions and saccharidic tracers. Details of sampling and extraction processes are described in the literature …”

“…Saccharides in filter blanks are below the detection limit. Detailed analytical procedures can be found in the literature noted above. ,,, Given the negligible sea-salt contribution (<5%) to PM 2.5 in our study region, , the non-sea-salt components are not corrected for.…”

“…Details of sampling and extraction processes are described in the literature. 22 2.2. Quadruple Sulfur Isotope Measurements and Evaluations of Precision and Accuracy.…”

“…Cosmogenic 35 S was measured by a newly developed liquid scintillation counter (Quantulus GCT 6220, PerkinElmer) method and corrected for background activities of blank filters. 22 Concentrations of water-soluble ions (K + , Mg 2+ , Ca 2+ , NO 3 − , SO 4 2− ) and saccharides (levoglucosan, mannosan, arabitol, mannitol, glucose) were measured by ion chromatography (883 Basic IC plus, Metrohm) at GIGCAS 30 and a HPAEC-PAD (highperformance anion exchange chromatography with pulsed amperometric detection) system (ICS-3000, Dionex) at South China Institute of Environmental Sciences, 11,21 respectively. Although Na + , Cl − , and NH 4 + were also measured, these data are not reported in this study because Na + and Cl − backgrounds in our filters are high and the collected NH 4 + is easily lost from high-alkalinity glass-fiber filters via NH 3 volatilization.…”

Generation of zero-valent sulfur from dissimilatory sulfate reduction in sulfate-reducing microorganisms

“…Since ZVS was mainly present as elemental sulfurs (S 0 ), we treated the radiolabeled elemental sulfurs as radiolabeled ZVS ( 35 S-ZVS) that was extracted with carbon tetrachloride for quantitative analysis. Then, 0.5 mL sample containing different sulfur species was mixed with 2 mL of 30% H 2 O 2 , 2.5 mL of deionized water, and 10 mL scintillation cocktail (Ultima Gold LLT; PerkinElmer) for subsequent scintillation counting on a Quantulus GCT 6220 liquid scintillation analyzer (PerkinElmer) following the high-sensitivity radiosulfur analytical technique developed for natural abundance radiosulfur measurements ( 54 , 55 ). Given that the aim of these radiosulfur-labeled experiments was to semiquantitatively identify the source of ZVS, we reported our data in the unit of cpm (counts per minute) and did not correct for the background or counting efficiency to obtain activities at units of disintegration per minute or Bq.…”