Continuous CO2 Monitoring Research Articles

Air-permeable redox mediated transcutaneous CO2 sensor

Standard clinical care of neonates and the ventilation status of human patients affected with coronavirus disease involves continuous CO2 monitoring. However, existing noninvasive methods are inadequate owing to the rigidity of hard-wired devices, insubstantial gas permeability and high operating temperature. Here, we report a cost-effective transcutaneous CO2 sensing device comprising elastomeric sponges impregnated with oxidized single-walled carbon nanotubes (oxSWCNTs)-based composites. The proposed device features a highly selective CO2 sensing response (detection limit 155 ± 15 ppb), excellent permeability and reliability under a large deformation. A follow-up prospective study not only offers measurement equivalency to existing clinical standards of CO2 monitoring but also provides important additional features. This new modality allowed for skin-to-skin care in neonates and room-temperature CO2 monitoring as compared with clinical standard monitoring system operating at high temperature to substantially enhance the quality for futuristic applications.

A new Multi-GAS system for continuous monitoring of CO2/ CH4 ratios at active volcanoes

We have designed, built, and tested a new Multi-GAS instrument which includes a CH4 sensor, along with CO2, H2O, and H2S sensors. We conducted laboratory-based experiments to calibrate the sensors, analyze possible cross-interferences among sensors, and evaluate the quality of the measurements. The results of these experiments demonstrate high-quality measurements with each sensor, with no cross-interferences and accurate and precise CO2/CH4 concentration ratios. These promising results from the laboratory experiments were validated with field measurements. We tested the new Multi-GAS instrument at four different sites on the flanks of Rincón de la Vieja and Miravalles volcanoes in Costa Rica. At each site, direct samples were also collected to compare these results to the Multi-GAS measurements. The results from direct sampling and Multi-GAS showed excellent agreement. These field tests confirmed that this Multi-GAS instrument has the potential to shed new light upon the dynamic interactions of magmatic systems with hydrothermal systems and therefore could help forecast phreatic and other types of volcanic eruptions.

Integrated near-infrared QEPAS sensor based on a 28 kHz quartz tuning fork for online monitoring of CO2 in the greenhouse

In this paper, a highly sensitive and integrated near-infrared CO2 sensor was developed based on quartz-enhanced photoacoustic spectroscopy (QEPAS). Unlike traditional QEPAS, a novel pilot line manufactured quartz tuning fork (QTF) with a resonance frequency f0 of 28 kHz was employed as an acoustic wave transducer. A near-infrared DFB laser diode emitting at 2004 nm was employed as the excitation light source for CO2 detection. An integrated near-infrared QEPAS module was designed and manufactured. The QTF, acoustic micro resonator (AmR), gas cell, and laser fiber are integrated, resulting in a super compact acoustic detection module (ADM). Compared to a traditional 32 kHz QTF, the QEPAS signal amplitude increased by > 2 times by the integrated QEPAS module based on a 28 kHz QTF. At atmospheric pressure, a 5.4 ppm detection limit at a CO2 absorption line of 4991.25 cm−1 was achieved with an integration time of 1 s. The long-term performance and stability of the CO2 sensor system were investigated using Allan variance analysis. Finally, the minimum detection limit (MDL) was improved to 0.7 ppm when the integration time was 125 s. A portable CO2 sensor system based on QEPAS was developed for 24 h continuous monitoring of CO2 in the greenhouse located in Guangzhou city. The CO2 concentration variations were clearly observed during day and night. Photosynthesis and respiration plants can be further researched by the portable CO2 sensor system.

Non-invasive carbon dioxide monitoring in neonates: methods, benefits, and pitfalls.

Wide fluctuations in partial pressure of carbon dioxide (PaCO2) can potentially be associated with neurological and lung injury in neonates. Blood gas measurement is the gold standard for assessing gas exchange but is intermittent, invasive, and contributes to iatrogenic blood loss. Non-invasive carbon dioxide (CO2) monitoring has become ubiquitous in anesthesia and critical care and is being increasingly used in neonates. Two common methods of non-invasive CO2 monitoring are end-tidal and transcutaneous. A colorimetric CO2 detector (a modified end-tidal CO2 detector) is recommended by the International Liaison Committee on Resuscitation (ILCOR) and the American Academy of Pediatrics to confirm endotracheal tube placement. Continuous CO2 monitoring is helpful in trending PaCO2 in critically ill neonates on respiratory support and can potentially lead to early detection and minimization of fluctuations in PaCO2. This review includes a description of the various types of CO2 monitoring and their applications, benefits, and limitations in neonates.

Ionic Liquid Impedance Sensor for Continuous Low Temperature CO2 monitoring

There is a significant need to develop sensor technology for applications in extreme environmental conditions. Robust gas sensors that can continuously monitor specific gaseous analytes in harsh environments are essential for a variety of applications such as environmental monitoring and greenhouse gas emissions in Arctic where temperatures are constantly in the sub-zero range. For efficient operation and long-term stability, these devices require sensing materials that can function at subzero temperatures as well as non-invasive readout mechanisms. Electrochemical techniques are advantageous for continuous gas sensing due to their cost effectiveness, simplicity, portability and easy miniaturization of the instrumentation. However, the application of constant or varying DC potential in commonly used voltametric and amperometric detection methods may result in interfacial redox reactions and formation of new products that could poison the sensor materials and take part in unfavorable side reactions. Electrochemical impedance spectroscopy (EIS) is a non-invasive alternate technique which measures impedance changes originating from change in polarization of the electrode-electrolyte interface upon addition of analyte gases. Compared to traditional aqueous electrolytes, the unique solvent and electrolyte properties of ionic liquids (ILs) enable them to operate in extreme environments without undergoing physical or chemical changes. In this presentation, we will discuss our results for the development of an ionic liquid (IL) based miniaturized impedance sensor for continuous CO2 monitoring in the -15 to 40oC temperature range using a microfabricated electrochemical sensor designed and fabricated with Pt black electrodes and hydrophobic [Bmpy][NTf2] ionic liquid electrolyte. The large hydrophobic NTf2 anion is shown to weaken cation−anion interactions, enabling a higher absorptivity of CO2. It also weakens water−anion interactions and thus impedes the absorption of H2O, minimizing the interference from humidity at the ambient conditions. Pt black provides a high surface area that allows simple and robust fabrication of planar electrodes on flexible polymer membranes. A non-invasive single frequency impedance spectroscopy (SF-EIS) method was demonstrated for the continuous and quantitative detection of CO2. In this method, impedance changes arising from increasing amounts of added CO2 analyte and [Bmpy][NTf2] IL at open circuit potential were measured at a set frequency of 1 Hz at different temperatures. It was seen that the impedance increased with decreasing temperature, and decreased with increasing amounts of added CO2. A linear relationship between the CO2 gas concentration and impedance was obtained, and increased sensitivity for CO2 detection was observed at low temperatures with a maximum slope of -5.092 ohm/%CO2 seen at -15oC. The same miniaturized and flexible planar electrochemical sensor with [Bmpy][NTf2] IL electrolyte was tested repeatedly for continuous sensing of CO2 at subzero temperatures over a two and a half month period, during which good stability and repeatability were obtained. To explain our impedance trend, we hypothesize that the high viscosity of IL at low temperature will result in the formation of a more packed, concentrated layer of ionic charges on the electrode surface. In the presence of CO2, the relatively rigid IL-electrode double layer at low temperature can be beneficial for chemical sensing since the molecular interactions between the CO2 analyte and [Bmpy][NTf2] could result in decreasing resistance and increasing conductivity by decreasing ionic attractions in the IL. Consequently, the high viscosity of ILs at low temperature, which is usually considered a limitation to practical in amperometric sensing, converts to an advantage in impedance sensing since ordered and concentrated electric double layer could provide high sensitivity and selectivity. In addition, the increased initial impedance at low temperature due to high IL viscosity and density is beneficial for our signal-off sensing mechanism. This reported CO2 sensor is among the first impedance based gas sensors shown to function continuously at sub-zero temperatures, providing CO2 measurements with good sensitivity at low cost and low power. These results obtained from our sensor show promise for potential use in real-time monitoring of carbon dioxide emissions in harsh low temperature environments, uniting the benefits of minimally invasive impedance transduction methods and robust IL sensing materials. Figure 1

Sensitivity optimisation of tuberculosis bioaerosol sampling.

Detection of Mycobacterium tuberculosis (Mtb) in patient-derived bioaerosol is a potential tool to measure source case infectiousness. However, current bioaerosol sampling approaches have reported low detection yields in sputum-positive TB cases. To increase the utility of bioaerosol sampling, we present advances in bioaerosol collection and Mtb identification that improve detection yields. A previously described Respiratory Aerosol Sampling Chamber (RASC) protocol, or "RASC-1", was modified to incorporate liquid collection of bioaerosol using a high-flow wet-walled cyclone (RASC-2). Individuals with GeneXpert-positive pulmonary TB were sampled pre-treatment over 60-minutes. Putative Mtb bacilli were detected in collected fluid by fluorescence microscopy utilising DMN-Trehalose. Exhaled air and bioaerosol volumes were estimated using continuous CO2 monitoring and airborne particle counting, respectively. Mtb capture was calculated per exhaled air volume sampled and bioaerosol volume for RASC-1 (n = 35) and for RASC-2 (n = 21). Empty chamber samples were collected between patients as controls. The optimised RASC-2 protocol sampled a median of 258.4L (IQR: 226.9-273.6) of exhaled air per patient compared with 27.5L (IQR: 23.6-30.3) for RASC-1 (p<0.0001). Bioaerosol volume collection was estimated at 2.3nL (IQR: 1.1-3.6) for RASC-2 compared with 0.08nL (IQR: 0.05-0.10) for RASC-1 (p<0.0001). The detection yield of viable Mtb improved from 43% (median 2 CFU, range: 1-14) to 95% (median 20.5 DMN-Trehalose positive bacilli, range: 2-155). These improvements represent a lowering of the limit of detection in the RASC-2 platform to 0.9 Mtb bacilli per 100L of exhaled air from 3.3 Mtb bacilli per 100L (RASC-1). This study demonstrates that technical improvements in particle collection together with sensitive detection enable rapid quantitation of viable Mtb in bioaerosols of sputum positive TB cases. Increased sampling sensitivity may allow future TB transmission studies to be extended to sputum-negative and subclinical individuals, and suggests the potential utility of bioaerosol measurement for rapid intervention in other airborne infectious diseases.

Origin and hazard of CO2 and H2S emissions in the Lavinio-Tor Caldara zone (Metropolitan City of Rome Capital, Italy)

Gas hazard was evaluated at Lavinio-Tor Caldara, the southernmost gas-discharging zone of the quiescent Albani Hills volcano in central Italy. Also this zone, like the other gas discharges of this volcanic complex, is located above a structural high of the buried Mesozoic carbonate basement, which represents the main reservoir for gas rising from depth. All extensional faults affecting the carbonates are leaking pathways along which gas may rise to the surface creating hazardous conditions. Gas is dominated by CO2 (>90 vol%) and the second component at Lavinio-Tor Caldara is H2S that displays the highest content (4.0–6.3 vol%) of all gas manifestations of the Rome region. This H2S enrichment corresponds to a marked decrease in 3He/4He (R/Ra) isotopic ratio suggesting that gas was contaminated in an upper crustal environment. The main gas discharge occurs at the natural reserve of Tor Caldara, in zones where past sulphur mining excavations removed the surficial impervious cover, or along a ditch. Comparison of the results of four soil CO2 flux surveys carried out in 2005–2018 at Miniera Grande within Tor Caldara, indicates that the highest soil CO2 release occurs shortly after local earthquakes. Continuous monitoring of CO2 and H2S air concentration and of wind speed has been carried out for four months in twelve anomalous gas realising sites of Tor Caldara. Results indicate that only H2S reaches lethal concentration (>250 ppm) near the soil in no wind nights, explaining the presence of small dead animals. At Lavinio, the main soil gas release occurs near old water wells that likely produced a gas blowout during drilling. A total release of over 20 tons/day from 2.93 km2 of gas of endogenous origin, has been estimated for the Lavinio-Tor Caldara area by a detailed soil CO2 flux survey (2572 measurement points over an area of 3.65 km2). The main structural lineaments of the area have N-S and W-E directions, but also NE-SW and NW-SE directions are well represented. Some sectors of the investigated area are exposed to a severe gas hazard for people and animals and precautionary measures should be adopted.

Carbon Dioxide Fluctuations Are Associated with Changes in Cerebral Oxygenation and Electrical Activity in Infants Born Preterm

To evaluate the effects of acute arterial carbon dioxide partial pressure changes on cerebral oxygenation and electrical activity in infants born preterm. This retrospective observational study included ventilated infants born preterm with acute fluctuations of continuous end-tidal CO2 (etCO2) as a surrogate marker for arterial carbon dioxide partial pressure, during the first 72 hours of life. Regional cerebral oxygen saturation and fractional tissue oxygen extraction were monitored with near-infrared spectroscopy. Brain activity was monitored with 2-channel electroencephalography. Spontaneous activity transients (SATs) rate (SATs/minute) and interval between SATs (in seconds) were calculated. Ten-minute periods were selected for analysis: before, during, and after etCO2 fluctuations of ≥5 mm Hg. Thirty-eight patients (mean ± SD gestational age of 29 ± 1.8 weeks) were included, with 60 episodes of etCO2 increase and 70 episodes of etCO2 decrease. During etCO2 increases, brain oxygenation increased (regional cerebral oxygen saturation increased, fractional tissue oxygen extraction decreased; P < .01) and electrical activity decreased (SATs/minute decreased, interval between SATs increased; P < .01). All measures recovered when etCO2 returned to baseline. During etCO2 decreases, brain oxygenation decreased (regional cerebral oxygen saturation decreased, fractional tissue oxygen extraction decreased; P < .01) and brain activity increased (SATs/minute increased, P < .05), also with recovery after return of etCO2 to baseline. An acute increase in etCO2 is associated with increased cerebral oxygenation and decreased brain activity, whereas an acute decrease is associated with decreased cerebral oxygenation and slightly increased brain activity. Combining continuous CO2 monitoring with near-infrared spectroscopy may enable the detection of otherwise undetected fluctuations in arterial carbon dioxide partial pressure that may be harmful to the neonatal brain.

Noninvasive monitoring of CO2 during polysomnography: a review of the recent literature.

Sleep-related breathing disorders are complex conditions that require the integration of clinical and sleep laboratory findings to support a diagnosis. Analysis of carbon dioxide (CO2) levels during sleep provides important additional information to the clinician that is not obtained from other polysomnographic indices, and that may have a direct impact on both diagnosis and patient mortality. Although arterial blood gas (ABG) is considered the gold standard for assessing PaCO2 levels, there are numerous drawbacks. Noninvasive methods for PaCO2 estimation include end-tidal and transcutaneous monitoring, which allow for continuous monitoring of trends. Review of the recent literature suggests that transcutaneous methods correlate strongly with PaCO2 levels and can provide an accurate surrogate in replacement of ABGs. End-tidal methods provide breath to breath information that can be used to assess hypoventilation; however, they have more variability, especially in patients with increased dead space and small tidal volumes. To date, however, there are limited studies investigating noninvasive CO2 monitoring during sleep. Given the benefits of CO2 monitoring and the importance of assessing for hypercapnia, noninvasive continuous CO2 monitoring should be considered for all patients undergoing polysomnography.

Transcutaneous carbon dioxide monitoring for the prevention of neonatal morbidity and mortality.

Carbon dioxide (CO2) measurement is a fundamental evaluation in a neonatal intensive care unit (NICU), as both low and high values of CO2 might have detrimental effects on neonatal morbidity and mortality. Though measurement of CO2 in the arterial blood gas is the most accurate way to assess the amount of CO2, it requires blood sampling and it does not provide a continuous monitoring of CO2. To assess whether the use of continuous transcutaneous CO2 (tcCO2) monitoring in newborn infants reduces mortality and improves short and long term respiratory and neurodevelopmental outcomes. We used the standard search strategy of the Cochrane Neonatal Review group to search the Cochrane Central Register of Controlled Trials (CENTRAL 2015, Issue 11), MEDLINE via PubMed (1966 to November 1, 2015), EMBASE (1980 to November 1, 2015), and CINAHL (1982 to November 1, 2015). We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomized controlled trials and quasi-randomized trials. Randomized, quasi-randomized and cluster randomized controlled trials comparing different strategies regarding tcCO2 monitoring in newborns. Three comparisons were considered, that is, continuous tcCO2 monitoring versus 1) any intermittent modalities to measure CO2; 2) other continuous CO2 monitoring; and 3) with or without intermittent CO2 monitoring. We used the standard methods of the Cochrane Neonatal Review Group. Two review authors independently assessed studies identified by the search strategy for inclusion. Our search strategy yielded 106 references. Two review authors independently assessed all references for inclusion. We did not find any completed studies for inclusion, nor ongoing trials. There was no evidence to recommend or refute the use of transcutaneous CO2 monitoring in neonates. Well-designed, adequately powered randomized controlled studies are necessary to address efficacy and safety of transcutaneous CO2 monitoring in neonates.

Oxygen mask capnometry typeR is useful device for continuous CO2 monitoring during different breathing patterns in extubated post abdominal surgical patients: a prospective observational study

Oxygen mask capnometry typeR is useful device for continuous CO2 monitoring during different breathing patterns in extubated post abdominal surgical patients: a prospective observational study

Portable dual-channel gas analyzer for continuous monitoring of carbon dioxide in gas streams

Abstract Development, characterization and application of a portable dual-channel analyzer based on gravity driven flow for continuous monitoring of CO2 in gas streams are presented. The analyzer is constructed from (i) a carrier/stripping solution reservoir, (ii) a diffusion scrubber (DS) in the form of a hollow fiber membrane (HFM) module integrated with a custom-designed flow-through pH-detector cell, and (iii) a waste solution reservoir. The analyzer is designed in such a way that the dilute sodium bicarbonate carrier/stripping solution flows downward by gravity into the lumen side of the hollow fibers in the HFM module which allows efficient contact with the gas stream. Absorption of CO2 into the carrier solution produces pH changes that constituted the analytical signal. Flat-bottom glass electrode and solid-state IrO2 electrodes were used as pH detectors in two types of custom-built flow cells, respectively. Under the optimized conditions, the measured pH signal showed Nernstian response to the CO2 concentration (59.6 and 62.0 mV/log[CO2] and r2 = 0.9992 and 0.9984 for the glass and IrO2 pH detectors, respectively) in the gas stream over a wide dynamic range (0.1-100 % CO2 in balance of nitrogen). Moreover, the presented analyzer based on either detector offered several favorable performance characteristics such as reasonably short response and recovery times; excellent signal stability and reproducibility and high selectivity in the presence of non-ionogenic gases, e.g., CH4, N2, O2, CO, etc. The suggested analyzer was applied successfully in the dual-channel monitoring of CO2 absorption from CO2-CH4 binary feed gas mixtures.

M1482: Quantitative and Qualitative Assessment of the Oxygen Delivery and EtCO2 Sampling During an Upper Endoscopy Procedure With the Oridion Smart Capnoline Guardian

The Oridion Smart Bite Bloc O2 Set (MD) is an airway management system intended for continuous monitoring of CO2, EtCO2 and respiration rate whilst providing oxygen before, during and after upper endoscopy procedures requiring the use of a Bite Bloc(EUS,ERCP). The device was cleared by FDA in 2004. The device includes a Bite Bloc integrated with a CO2 oral/nasal sampling line and simultaneously enabling oxygen provision to the patient.The modified version of the device (DUT) was designed to provide improved CO2 sampling and oxygen delivery and increased ease of use.It includes:1.oral nasal oxygen delivery option with up to 10L/min in place of the nasal only delivery in the previous device with up to 5L/min.2.improved anchoring of the oral CO2 sampling prong.3.addition of an optional gum comfort pad to provide a better grip for patients missing teeth.

Disturbed Sleep in a Patient with Duchenne Muscular Dystrophy

Disturbed Sleep in a Patient with Duchenne Muscular Dystrophy

Severe Hypercapnia during Cardiopulmonary Bypass due to Carbon Dioxide Insufflation - A case report -

Air embolization is a potential danger during open heart surgery. To prevent air embolization in incompletely deaired cardiac chambers, flooding of the surgical fields with carbon dioxide (CO2) is used during cardiopulmonary bypass. CO2 flooding may be more useful in de-airing for patients undergoing minimally invasive cardiac surgery. We experienced an episode of sudden, severe hypercapnia and respiratory acidosis in a 51-year-old female patient during hypothermic cardiopulmonary bypass for minimally invasive mitral valve replacement. During hypercapnia, hemodynamic and BIS data were stable except for a slight increase in mean arterial pressure. After ruling out other causes of hypercapnia such as oxygenator failure and malignant hyperthermia, severe hypercapnia disappeared gradually after the cessation of CO2 flooding in the surgical field. No neurologic or cardiopulmonary complications were noted after the operation. We concluded that frequent or continuous CO2 monitoring may be required during CO2 insufflation at surgical fields to prevent hypercapnic complications in minimally invasive cardiac surgery. (Korean J Anesthesiol 2008; 54: 94∼7)

Ventilatory assistance in patients with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) leads to progressive muscle weakness, causing respiratory failure 1, 2. Untreated patients die at <25 yrs of age, and the mean age of death in the 1960s was 15 yrs. The introduction of mechanical ventilation has improved survival compared with historical controls 1–3. This finding has led to general agreement that noninvasive ventilation prolongs life in patients with DMD, although no controlled studies have been performed to confirm this hypothesis 4. Noninvasive mechanical ventilation is initially offered at night to treat sleep-related breathing disorders and hypoventilation, which are common in patients with DMD 5, 6. Breathing during sleep should be evaluated by polysomnography with continuous CO2 monitoring 7, or by continuous CO2 monitoring alone if polysomnography is not available. Overnight pulse oximetry combined with an early-morning arterial blood gas measurement (to detect a base excess) may also be used to monitor nocturnal ventilation. As the disease progresses, hypoventilation starts to occur during the daytime, and additional daytime ventilation is offered 4. When noninvasive mechanical ventilation is inadequately effective, poorly tolerated or not feasible owing to …

Seismo-Geochemical Variations in SW Taiwan: Multi-Parameter Automatic Gas Monitoring Results

Gas variations of many mud volcanoes and hot springs distributed along the tectonic sutures in southwestern Taiwan are considered to be sensitive to the earthquake activity. Therefore, a multi-parameter automatic gas station was built on the bank of one of the largest mud-pools at an active fault zone of southwestern Taiwan, for continuous monitoring of CO2, CH4, N2 and H2O, the major constituents of its bubbling gases. During the year round monitoring from October 2001 to October 2002, the gas composition, especially, CH4 and CO2, of the mud pool showed significant variations. Taking the CO2/CH4 ratio as the main indicator, anomalous variations can be recognized from a few days to a few weeks before earthquakes and correlated well with those with a local magnitude >4.0 and local intensities >2. It is concluded that the gas composition in the area is sensitive to the local crustal stress/strain and is worthy to conduct real-time monitoring for the seismo-geochemical precursors.

A TGA/FT-IR study for measuring OC and EC in aerosol samples

Abstract. Carbon analysis consists in the evaluation of the carbonaceous content of the aerosol (TC) but, more importantly, of its distribution between the two components EC (Elemental Carbon) and OC (Organic Carbon) that are characterized by different physical-chemical properties. In spite of the numerous studies focused on this topic, nowadays a universal methodology for the determination of the two components EC and OC is not available. In fact OC and EC (also known as black carbon or soot) are operationally defined by the method of analysis and, as a consequence, different methods can produce different results. In this paper we present results on the application of TGA/FT-IR (Thermo-gravimetric Analysis/Fourier Transformed Infrared Spectroscopy) to the characterization of carbonaceous aerosols. The analytical methodology was applied to PM10 (particulate matter with aerodynamic diameter smaller than 10 μm) four-hour time resolution samples collected in Milan urban area. The method is a two-steps thermal one and it is based on the different thermal behaviour of OC and EC. It has been set up analyzing suitable standards containing both organic and elemental carbon. Carbon quantification is achieved by on-line, continuous monitoring of CO2 infrared absorption at 2361 cm−1. A good separation between OC and EC on particulate matter (PM) samples has been obtained. Ranges and average values were 12–70 μg/m3 and 20 μg/m3 for OC and 0.2–6 μg/m3 and 2 μg/m3 for EC. On average OC and EC made up 29 (±13)% and 2.5 (±1.8)% of the PM10 fraction, respectively. The method reliability has been verified by a preliminary comparison with TOT (Thermal Optical Transmission) technique. OC and EC values determined for ambient samples of PM10 were correlated with meteorological parameters as well as with Radon concentrations.

A diode-laser-based spectrometer for in-situ measurements of volcanic gases

We report the first results of the field operation of a novel, portable diode-laser spectrometer for gas-concentration measurements in volcanic areas. Remote detection of direct absorption line shapes was possible thanks to a telecom single-mode optical fiber that delivered radiation from a room-temperature distributed-feedback diode laser, emitting at 1.997 μm, to an open-path multiple-reflection cell, placed on gas effluxes. The system was deployed on two different active volcanoes in Italy, where simultaneous and continuous monitoring of CO2 and H2O concentrations has been demonstrated.

Temperature effects on release and ecologically relevant properties of dissolved organic carbon in sterilised and biologically active soil samples

To evaluate the effects of temperature and biological activity on the release and quality of dissolved organic carbon (DOC), incubation experiments were conducted with soil from the Ap-horizon of a Gleyic Fluvisol (sandy clay loam, pH 7.2; 6.4% C org). Samples were either non-sterile, sterilised by γ-irradiation or reinoculated after sterilisation. Incubations were performed at three temperatures: 5, 20 and 35 °C for 12 days with continuous CO 2-monitoring. DOC was obtained by percolating the samples before and after incubation with 1 mM CaCl 2 solution. DOC quality was assessed by ultra-filtration, UV-absorbance, Cu-complexation capacity and biodegradability. In the sterile samples, DOC-concentrations were hardly affected by incubation temperature and among the quality parameters, only the UV-absorbance of DOC decreased with increasing incubation temperature in all size fractions. In the reinoculated and non-sterile samples, DOC-concentrations decreased strongly with increasing incubation temperature. This was closely related to respiration activity and accompanied by increases in Cu-complexation capacity and biodegradability. In the larger DOC size fractions separated by ultra-filtration (MWCO>1000), UV-absorbance increased after incubation at higher temperatures. The results show that DOC is readily utilised as substrate by microorganisms and at the same time modified in its composition by selective degradation of UV-inactive compounds and by the release of low molecular, easily degradable compounds with high Cu-complexation capacity.