diffusive

Active real-time analyzers vs. passive/diffusive samplers for hydrogen sulfide (H2S) concentrations in air: a critical comparison 1,2 Venturi S. ,

1,2 Cabassi J. ,

1,2 Tassi F. ,

1,2 Capecchiacci F. ,

1,2 Vaselli O. ,

3 4 Bellomo S. , Calabrese S.

1) Dipartimento di Scienze della Terra, University of Florence, Via G. La Pira 4, 50121 Florence (Italy) 2) CNR – Istituto di Geoscienze e Georisorse, Via G. La Pira 4, 50121 Florence (Italy)

3) Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, 90123 Palermo (Italy) 4) Dipartimento di Scienze della Terra e del Mare, University of Palermo, Via Archirafi 36, 90123 Palermo (Italy)

INTRODUCTION The development of efficient techniques for the determination of airborne pollutant concentrations is a primary issue in environmental monitoring. Reliable measurements of toxic gases are critical for accurate estimations of air quality, identification of contaminant sources, characterization of atmospheric transport, and rapid individuation of health hazards. Two main measuring methods are currently used in environmental applications: • passive samplers: low-cost portable devices, operating according to the Fick’s first law (i.e. gaseous molecules move following a concentration gradient from areas of high concentration to low concentrations). • active real-time analyzers: high-frequency data acquiring instruments with promptly-readible concentration measurements. Their application to spatial monitoring of air quality could be challenging due to their cost, requirement of frequent calibration and need of constant power supply. Although passive samplers offer an appealing alternative to real-time measurements, particularly for regional-scale monitoring, their reliability in outdoor applications strongly depends on several environmental factors, such as air temperature, humidity and wind speed (Delgado-Saborit & Esteve-Cano, 2006). In this study a comparison between H2S measurements using both diffusive radial-type passive samplers (Radiello) and a real-time gas analyzer (Thermo Scientific Model 450i) is presented. The measurements were carried out in areas affected by both anthropogenic (landfills, urban sites, geothermal power plants) and natural sources (volcanic and hydrothermal systems).

References Delgado-Saborit J.M. & Esteve-Cano V., 2006. Field study of diffusion collection rate coefficients of a NO2 passive sampler in a Mediterranean coastal area. Environ Monit Assess, 120, 327-345. Fondazione Maugeri, 2007. Instruction Manual for Radiello Sampler. http://www.radiello.com/english/index_en.html Pavilonis B.T., O'Shaughnessy P.T., Altmaier R., Metwali N. & Thorne P.S., 2013. Passive monitors to measure hydrogen sulfide near concentrated animal feeding operations. Environ Sci Process Impacts, 15(6), 1271-1278, doi:10.1039/c3em00082f. Schiffman S.S. & Williams C.M., 2005. Science of odor as a potential health issue. J Environ Qual, 34, 129–138. Thermo Fisher Scientific Inc, 2012. Thermo Scientific Model 450i Hydrogen Sulfide & Sulfur Dioxide Analyzer Manual. https://www.thermoscientific.com WHO, 2000. Air Quality Guidelines for Europe, second edition. WHO Regional Publications, European Series, No. 91.

detectable odor annoyance 24h threshold threshold odor

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RESULTS Measurements were carried out over a wide range of H2S concentrations (from 2000 μg/m3) with exposure duration (from 52 to 206 minutes) increasing with decreasing concentrations. The wind speeds averaged over each sampling period were 100 %. Large temporal variations of the H2SThermo concentrations were observed in most measuring sites (Fig. 3). Vice versa, since passive samplers integrate and smooth the H2S realtime concentrations, short-term increments up to annoying levels were not recorded by Radiello samplers.

Fig. 3 160

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H2S (g/m3)

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THERMO SCIENTIFIC MODEL 450i H2S REAL-TIME ANALYZER The Thermo Scientific Model 450i gas analyzer utilizes a pulsed fluorescence technology to determine the concentrations of gaseous sulfur species in ambient air (Thermo Scientific, 2012). In particular, the instrument measures the UV light emitted by SO2 molecules excited by a pulsing UV source lamp. Therefore, the analyzer needs H2S to be converted to SO2 (conversion efficiency: >80 %). The air pumped by the instrument at a flow rate of 1 L/min alternatively bypasses the converter and goes through it, the gas analyzer measuring SO2 and CS (Combined Sulfur, i.e. SO2+H2S) contents, respectively. The difference between the two signals is the H2S content. The detection limit is 1.4 μg/m3 , with a precision of 1 % (Thermo Scientific, 2012).

Fig. 1

H2SRadiello (g/m3)

RADIELLO PASSIVE/DIFFUSIVE SAMPLERS Radiello H2S passive samplers are static sampling devices with a peculiar radial design of the diffusive body that allows a higher uptake rate and a greater sensitivity. The adsorbent cartridge is made of Diffusive Adsorbent body cartridge microporous polyethylene impregnated with zinc acetate. As H2S reacts with the organic salt, stable zinc sulfide forms. In the lab, ZnS is solubilized in water and analyzed via visible spectrometry (Fondazione Maugeri, 2007). The recommended exposure duration varies from 1 hour to 15 days, with detection limits of 42 μg/m3 and 1.4 μg/m3 for 1 hour and 24 hours exposures, respectively (uncertainty at 2σ: 8.7 %; Fondazione Maugeri, 2007).

HYDROGEN SULFIDE (H2S) Hydrogen sulfide (H2S) is a highly toxic gas, largely emitted in the atmosphere by both natural (mainly volcanic and hydrothermal systems) and anthropogenic activities (e.g. sewage treatment plants, vehicular traffic, geothermal power plants, oil and gas refineries). Its peculiar rotten-egg smell is clearly detectable even at concentrations between 0.7 and 42 μg/m3 (Schiffman & Williams, 2005) and, when present, causes odor nuisance to neighbouring communities. In order to avoid significant odor annoyance among the exposed populations, H2S concentrations should not exceed 7 μg/m3 with an 30-minute averaging period (WHO, 2000). At high concentrations, H2S can irritate eyes, damage the upper respiratory tract, and cause loss of smell. The effects of long-term exposure to low levels (100%) to measure H2S concentrations close to the odor annoyance threshold (i.e. 7 μg/m3) over short term exposures (