Mark Zahniser - Academia.edu (original) (raw)

Papers by Mark Zahniser

Research paper thumbnail of OH Reaction Kinetics and Atmospheric Impact of 1-Bromopropane

Journal of Physical Chemistry A, Jul 1, 1997

Research paper thumbnail of Sex and Gender Bias in Illustrations in Anatomy and Physical Diagnosis Texts

Research paper thumbnail of The detection and surgical management of recurrent colon and rectal cancers

Cancer Treatment and Research, 1987

Early aggressive surgery is not the universally accepted procedure of choice for the management o... more Early aggressive surgery is not the universally accepted procedure of choice for the management of recurrent colorectal cancer. Barring patients with multiple, diffuse metastases, surgical excision for cure can be accomplished at a second operation, with one-third of the re-operated patients remaining free of disease indefinitely [1, 2]. Second-look operations and the pre-planned use of carcinoembryonic antigen (CEA) to indicate when to operate, though still questioned by some, is now showing significant clinical benefit along with long-term free-of-disease survival in many patients.

Research paper thumbnail of Intercomparison of fast response commercial gas analysers for nitrous oxide flux measurements under field conditions

Research paper thumbnail of Supplementary material to "Long-term fluxes of carbonyl sulfide and their seasonality and interannual variability in a boreal forest

Research paper thumbnail of Clumped methane isotopologue ( 13 CH 3 D) thermometry of geological methane by tunable mid-infrared laser spectroscopy

Research paper thumbnail of Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe’s terrestrial ecosystems: a review

International Agrophysics, 2018

Research infrastructures play a key role in launching a new generation of integrated long-term, g... more Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, sp...

Research paper thumbnail of Real-time measurement of δ13C and δ18O in CO2 by QCLAS - from the soil to the free troposphere

Isotope ratios of CO2 are highly valuable to investigate CO2 sources, sinks and transport at loca... more Isotope ratios of CO2 are highly valuable to investigate CO2 sources, sinks and transport at local and global scales. However, relevant studies often require extensive and long term measurements under field conditions, which may not be feasible with standard isotope ratio mass spectrometers (IRMS). We have developed and validated an entirely cryogen-free quantum cascade laser absorption spectrometer (QCLAS) using a room temperature 4.3 μm QC laser. The QCLAS is based on the differential absorption technique and suited for long-term, unattended field applications, delivering both δ13C and δ18O in CO2 with a precision of 0.05 permil. The spectrometer was validated against IRMS in laboratory and field studies, and has been employed in a range of studies, including forest soil respiration, grassland sub canopy respiration and long-term measurements at a remote location. In a beech forest of the Swiss Jura, we applied the QCLAS to investigate 13C and 18O dynamics of CO2 in a closed chamb...

Research paper thumbnail of New method for isotopic ratio measurements of atmospheric carbon dioxide using a 4.3 μm pulsed quantum cascade laser

Applied Physics B-lasers and Optics, 2008

We present a new approach to the measurement of stable isotopic ratios of carbon dioxide using a ... more We present a new approach to the measurement of stable isotopic ratios of carbon dioxide using a near-room-temperature pulsed quantum cascade laser and a spectral ratio method based upon dual multiple pass absorption cells. The spectral ratio method improves precision and accuracy by reducing sensitivity to variations in the laser tuning rate, power and line width. The laser is scanned

Research paper thumbnail of Towards a stable and absolute atmospheric carbon dioxide instrument using spectroscopic null method

Atmospheric Measurement Techniques, 2013

Research paper thumbnail of Direct measurements of HONO and NO2 by tunable infrared differential absorption spectroscopy; Results from two field campaigns sampling aircraft exhaust and ambient urban air

Nitrous acid (HONO) is an important source of hydroxyl radicals (OH), the main oxidizing agent in... more Nitrous acid (HONO) is an important source of hydroxyl radicals (OH), the main oxidizing agent in the atmosphere. However, gaseous HONO has historically proven difficult to measure accurately and to date there is no standard technique. We describe a new instrument capable of high-frequency measurements of HONO and nitrogen dioxide (NO2) mixing ratios by tunable infrared differential absorption spectrometry. Mid-infrared

Research paper thumbnail of Long-term fluxes of carbonyl sulfide and their seasonality and interannual variability in a boreal forest

. The seasonality and interannual variability of terrestrial carbonyl sulfide (COS) fluxes are po... more . The seasonality and interannual variability of terrestrial carbonyl sulfide (COS) fluxes are poorly constrained. We present the first easy-to-use parameterization for net COS forest sink based on the longest eddy covariance record from a boreal pine forest, covering 32 months over 5 years. Fluxes from hourly to yearly scales are reported, with the aim of revealing controlling factors and the level of interannual variability. The parameterization is based on the photosynthetically active radiation, vapor pressure deficit, air temperature, and leaf area index. The spring recovery of the flux after the winter dormancy period was mostly governed by air temperature, and the onset of the uptake varied by 2 weeks. For the first time, we report a significant reduction of ecosystem-scale COS flux under large water vapor pressure deficit in summer. The maximum monthly and weekly median COS uptake varied 26 and 20 % between years, respectively. The timing of the latter varied by 6 weeks. The fraction of the nocturnal uptake remained below 21 % of the total COS uptake. We observed the growing season (April–August) average net flux of COS totaling −58.0 gS ha−1 with 37 % interannual variability. The long-term flux observations were scaled up to evergreen needleleaf forests (ENFs) in the whole boreal region by the Simple Biosphere Model Version 4 (SiB4). The observations were closely simulated by using SiB4 meteorological drivers and phenology. The total COS uptake by boreal ENF was in line with a missing COS sink at high latitudes pointed out in earlier studies.

Research paper thumbnail of Continuous infusion chemotherapy, radiotherapy, and FDG‐PET are feasible during extracorporeal membrane oxygenation

Research paper thumbnail of ChemInform Abstract: Chemical Kinetics of the Reactions of the OH Radical with Several Hydrochlorofluoropropanes

Research paper thumbnail of Measuring oxygen fluxes in a European beech forest - results from the OXYFLUX project

<p>Ecosystem assimilation and respiration result in anti-correlated fluxes of oxyge... more <p>Ecosystem assimilation and respiration result in anti-correlated fluxes of oxygen (O<sub>2</sub>) and carbon dioxide (CO<sub>2</sub>). While the ecosystem O<sub>2</sub>:CO<sub>2</sub> molar exchange ratio is usually assumed constant at ≈1.1 on longer timescales, variations for individual ecosystem compartments or shorter timescales have been reported in the past. We hypothesize that these exchange ratio variations can reveal information about underlying biotic and abiotic processes in plants or soil that cannot be inferred from traditional net ecosystem exchange measurements. To date, oxygen measurements have not been widely implemented in ecosystem research due to the technical challenge of detecting very small variations (ppm-level) against an atmospheric background of ≈21% (≈210,000 ppm).</p> <p>We evaluate the performance and applicability of two commercial oxygen analyzers Integrated into custom-built gas handling and calibration systems, and report first results from measurements of O<sub>2</sub>:CO<sub>2</sub> exchange ratios in a managed European beech forest in central Germany.</p> <p>System 1, consisting of a relatively slow response differential fuel cell O<sub>2</sub> analyzer (Oxzilla FC-2, Sable Systems Inc., USA) together with a non-dispersive infrared CO<sub>2</sub> analyzer (LI-840, LI-COR Biosciences, USA), was used to simultaneously measure O<sub>2</sub> and CO<sub>2 </sub>mole fractions in air sampled from soil, stem, and branch chambers. Chambers were operated in an open flow-through steady-state design aimed at equilibrium mole fractions within a few hundred ppm of atmospheric background. Using a multiplexer valve design, we measured chambers sequentially by directing chamber air at a controlled flow rate to the gas analyzing system.</p> <p>Preliminary analysis of August to December 2018 data show that chamber-based flux estimates for O<sub>2</sub> and CO<sub>2</sub> were anti-correlated at all times, and that the O<sub>2</sub>:CO<sub>2</sub> molar exchange ratios (defined as ‑Δ[O<sub>2</sub>]/Δ[CO<sub>2</sub>]) varied considerably over time and between the different ecosystem compartments (soil, stems, and branches) with a median (interquartile range) of 0.94 (0.75 to 1.09).</p> <p>In system 2, CO<sub>2</sub>, O<sub>2</sub> and water vapor (H<sub>2</sub>O) measurements were performed with a fast response (5 Hz) gas analyzer using tunable infrared laser direct absorption spectroscopy (TILDAS, Aerodyne Research Inc., USA). We measured fluctuations in O<sub>2</sub>:CO<sub>2</sub> exchange ratios in air sampled at 1.5 times the canopy height, i.e. a typical eddy covariance set-up.</p> <p>Analysis of the high-frequency data revealed instrumental noise levels of ≈±12 ppm O<sub>2</sub>. Fourier transformation of high-frequency data obtained during well-mixed boundary layer conditions indicate that turbulent fluctuations of the O<sub>2</sub> signal were insufficiently resolved when compared to the CO<sub>2</sub> power spectra. When averaging high-frequency data to 2-min aggregates, instrumental noise was reduced to ≈±1 ppm, similar to the precision of system 1. At this timescale, contemporaneous measurements of above-canopy air revealed agreement between the fuel cell and the laser systems, both in O<sub>2</sub> mole fraction (R<sup>2</sup> = 0.6 slope = 0.7, MAE = 1.6 ppm) and in estimated O<sub>2</sub>:CO<sub>2</sub> exchange ratios of 1.01 and 0.97 for system 1 and 2, respectively.</p> <p>Our presentation will expand on the applicability of both O<sub>2</sub> and CO<sub>2 </sub>measurement systems with regard to micrometeorological flux techniques. Specifically, we elucidate on the potential of using O<sub>2 </sub>flux measurements as a constraint for estimating ecosystem-scale gross primary production.</p>

Research paper thumbnail of Standardisation of eddy-covariance flux measurements of methane and nitrous oxide

International Agrophysics

Commercially available fast-response analysers for methane (CH4) and nitrous oxide (N2O) have rec... more Commercially available fast-response analysers for methane (CH4) and nitrous oxide (N2O) have recently become more sensitive, more robust and easier to operate. This has made their application for long-term flux measurements with the eddy-covariance method more feasible. Unlike for carbon dioxide (CO2) and water vapour (H2O), there have so far been no guidelines on how to optimise and standardise the measurements. This paper reviews the state-of-the-art of the various steps of the measurements and discusses aspects such as instrument selection, setup and maintenance, data processing as well as the additional measurements needed to aid interpretation and gap-filling. It presents the methodological protocol for eddy covariance measurements of CH4 and N2O fluxes as agreed for the ecosystem station network of the pan-European Research Infrastructure Integrated Carbon Observation System and provides a first international standard that is suggested to be adopted more widely. Fluxes can be...

Research paper thumbnail of Uptake of gas-phase halogenated acetic acid molecules by water surfaces

The Journal of Physical Chemistry

ABSTRACT

Research paper thumbnail of Uptake of sulfur dioxide(G) by aqueous surfaces as a function of pH: the effect of chemical reaction at the interface

The Journal of Physical Chemistry

Research paper thumbnail of Uptake of gas-phase alcohol and organic acid molecules by water surfaces

The Journal of Physical Chemistry

It is now recognized that many important atmospheric reactions occur inside aqueous droplets of c... more It is now recognized that many important atmospheric reactions occur inside aqueous droplets of clouds and fogs. Recognition of the importance of these heterogeneous processes has stimulated an increasing amount of research in this area and a growing understanding about the nature of heterogeneous processes. Mass accommodation coefficients (α) have been measured as a function of temperature in the range

Research paper thumbnail of High-precision simultaneous 18O/16O, 13C/12C and 17O/16O analyses for µg-quantities of CaCO3 by tunable infrared laser absorption spectroscopy

Analytical Chemistry

Stable isotope ratios ((18)O/(16)O, (13)C/(12)C, and (17)O/(16)O) in carbonates have contributed ... more Stable isotope ratios ((18)O/(16)O, (13)C/(12)C, and (17)O/(16)O) in carbonates have contributed greatly to the understanding of Earth and planetary systems, climates, and history. The current method for measuring isotopologues of CO2 derived from CaCO3 is primarily gas-source isotope ratio mass spectroscopy (IRMS). However, IRMS has drawbacks, such as mass overlap by multiple CO2 isotopologues and contaminants, the requirement of careful sample purification, and the use of major instrumentation needing permanent installation and a high power electrical supply. Here, we report simultaneous (18)O/(16)O, (13)C/(12)C, and (17)O/(16)O analyses for microgram quantities of CaCO3 using a tunable mid-infrared laser absorption spectroscopy (TILDAS) system, which has no mass overlap problem and yields high sensitivity/precision measurements on small samples, as small as 0.02 μmol of CO2 (equivalent to 2 μg of CaCO3) with standard errors of less than 0.08 ‰ for (18)O/(16)O and (13)C/(12)C (±0.136 ‰ and ±0.387 ‰ repeatability; n = 10). In larger samples of CO2, 0.68 μmol (or 68 μg of CaCO3), standard error is less than 0.04 ‰ for (18)O/(16)O and (13)C/(12)C (< ±0.1 ‰ repeatability; n = 10) and 0.03 ‰ for (17)O/(16)O (±0.069 ‰ repeatability; n = 10). We also show, for the first time, the relationship between (17)O/(16)O ratios measured using the TILDAS system and published δ(17)O values of international standard materials (NBS-18 and -19) measured by IRMS. The benchtop TILDAS system, with cryogen-free sample preparation vacuum lines for microgram quantities of carbonates, is therefore a significant advance in carbonate stable isotope ratio geochemistry and is a new alternative to conventional IRMS.

Research paper thumbnail of OH Reaction Kinetics and Atmospheric Impact of 1-Bromopropane

Journal of Physical Chemistry A, Jul 1, 1997

Research paper thumbnail of Sex and Gender Bias in Illustrations in Anatomy and Physical Diagnosis Texts

Research paper thumbnail of The detection and surgical management of recurrent colon and rectal cancers

Cancer Treatment and Research, 1987

Early aggressive surgery is not the universally accepted procedure of choice for the management o... more Early aggressive surgery is not the universally accepted procedure of choice for the management of recurrent colorectal cancer. Barring patients with multiple, diffuse metastases, surgical excision for cure can be accomplished at a second operation, with one-third of the re-operated patients remaining free of disease indefinitely [1, 2]. Second-look operations and the pre-planned use of carcinoembryonic antigen (CEA) to indicate when to operate, though still questioned by some, is now showing significant clinical benefit along with long-term free-of-disease survival in many patients.

Research paper thumbnail of Intercomparison of fast response commercial gas analysers for nitrous oxide flux measurements under field conditions

Research paper thumbnail of Supplementary material to "Long-term fluxes of carbonyl sulfide and their seasonality and interannual variability in a boreal forest

Research paper thumbnail of Clumped methane isotopologue ( 13 CH 3 D) thermometry of geological methane by tunable mid-infrared laser spectroscopy

Research paper thumbnail of Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe’s terrestrial ecosystems: a review

International Agrophysics, 2018

Research infrastructures play a key role in launching a new generation of integrated long-term, g... more Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, sp...

Research paper thumbnail of Real-time measurement of δ13C and δ18O in CO2 by QCLAS - from the soil to the free troposphere

Isotope ratios of CO2 are highly valuable to investigate CO2 sources, sinks and transport at loca... more Isotope ratios of CO2 are highly valuable to investigate CO2 sources, sinks and transport at local and global scales. However, relevant studies often require extensive and long term measurements under field conditions, which may not be feasible with standard isotope ratio mass spectrometers (IRMS). We have developed and validated an entirely cryogen-free quantum cascade laser absorption spectrometer (QCLAS) using a room temperature 4.3 μm QC laser. The QCLAS is based on the differential absorption technique and suited for long-term, unattended field applications, delivering both δ13C and δ18O in CO2 with a precision of 0.05 permil. The spectrometer was validated against IRMS in laboratory and field studies, and has been employed in a range of studies, including forest soil respiration, grassland sub canopy respiration and long-term measurements at a remote location. In a beech forest of the Swiss Jura, we applied the QCLAS to investigate 13C and 18O dynamics of CO2 in a closed chamb...

Research paper thumbnail of New method for isotopic ratio measurements of atmospheric carbon dioxide using a 4.3 μm pulsed quantum cascade laser

Applied Physics B-lasers and Optics, 2008

We present a new approach to the measurement of stable isotopic ratios of carbon dioxide using a ... more We present a new approach to the measurement of stable isotopic ratios of carbon dioxide using a near-room-temperature pulsed quantum cascade laser and a spectral ratio method based upon dual multiple pass absorption cells. The spectral ratio method improves precision and accuracy by reducing sensitivity to variations in the laser tuning rate, power and line width. The laser is scanned

Research paper thumbnail of Towards a stable and absolute atmospheric carbon dioxide instrument using spectroscopic null method

Atmospheric Measurement Techniques, 2013

Research paper thumbnail of Direct measurements of HONO and NO2 by tunable infrared differential absorption spectroscopy; Results from two field campaigns sampling aircraft exhaust and ambient urban air

Nitrous acid (HONO) is an important source of hydroxyl radicals (OH), the main oxidizing agent in... more Nitrous acid (HONO) is an important source of hydroxyl radicals (OH), the main oxidizing agent in the atmosphere. However, gaseous HONO has historically proven difficult to measure accurately and to date there is no standard technique. We describe a new instrument capable of high-frequency measurements of HONO and nitrogen dioxide (NO2) mixing ratios by tunable infrared differential absorption spectrometry. Mid-infrared

Research paper thumbnail of Long-term fluxes of carbonyl sulfide and their seasonality and interannual variability in a boreal forest

. The seasonality and interannual variability of terrestrial carbonyl sulfide (COS) fluxes are po... more . The seasonality and interannual variability of terrestrial carbonyl sulfide (COS) fluxes are poorly constrained. We present the first easy-to-use parameterization for net COS forest sink based on the longest eddy covariance record from a boreal pine forest, covering 32 months over 5 years. Fluxes from hourly to yearly scales are reported, with the aim of revealing controlling factors and the level of interannual variability. The parameterization is based on the photosynthetically active radiation, vapor pressure deficit, air temperature, and leaf area index. The spring recovery of the flux after the winter dormancy period was mostly governed by air temperature, and the onset of the uptake varied by 2 weeks. For the first time, we report a significant reduction of ecosystem-scale COS flux under large water vapor pressure deficit in summer. The maximum monthly and weekly median COS uptake varied 26 and 20 % between years, respectively. The timing of the latter varied by 6 weeks. The fraction of the nocturnal uptake remained below 21 % of the total COS uptake. We observed the growing season (April–August) average net flux of COS totaling −58.0 gS ha−1 with 37 % interannual variability. The long-term flux observations were scaled up to evergreen needleleaf forests (ENFs) in the whole boreal region by the Simple Biosphere Model Version 4 (SiB4). The observations were closely simulated by using SiB4 meteorological drivers and phenology. The total COS uptake by boreal ENF was in line with a missing COS sink at high latitudes pointed out in earlier studies.

Research paper thumbnail of Continuous infusion chemotherapy, radiotherapy, and FDG‐PET are feasible during extracorporeal membrane oxygenation

Research paper thumbnail of ChemInform Abstract: Chemical Kinetics of the Reactions of the OH Radical with Several Hydrochlorofluoropropanes

Research paper thumbnail of Measuring oxygen fluxes in a European beech forest - results from the OXYFLUX project

<p>Ecosystem assimilation and respiration result in anti-correlated fluxes of oxyge... more <p>Ecosystem assimilation and respiration result in anti-correlated fluxes of oxygen (O<sub>2</sub>) and carbon dioxide (CO<sub>2</sub>). While the ecosystem O<sub>2</sub>:CO<sub>2</sub> molar exchange ratio is usually assumed constant at ≈1.1 on longer timescales, variations for individual ecosystem compartments or shorter timescales have been reported in the past. We hypothesize that these exchange ratio variations can reveal information about underlying biotic and abiotic processes in plants or soil that cannot be inferred from traditional net ecosystem exchange measurements. To date, oxygen measurements have not been widely implemented in ecosystem research due to the technical challenge of detecting very small variations (ppm-level) against an atmospheric background of ≈21% (≈210,000 ppm).</p> <p>We evaluate the performance and applicability of two commercial oxygen analyzers Integrated into custom-built gas handling and calibration systems, and report first results from measurements of O<sub>2</sub>:CO<sub>2</sub> exchange ratios in a managed European beech forest in central Germany.</p> <p>System 1, consisting of a relatively slow response differential fuel cell O<sub>2</sub> analyzer (Oxzilla FC-2, Sable Systems Inc., USA) together with a non-dispersive infrared CO<sub>2</sub> analyzer (LI-840, LI-COR Biosciences, USA), was used to simultaneously measure O<sub>2</sub> and CO<sub>2 </sub>mole fractions in air sampled from soil, stem, and branch chambers. Chambers were operated in an open flow-through steady-state design aimed at equilibrium mole fractions within a few hundred ppm of atmospheric background. Using a multiplexer valve design, we measured chambers sequentially by directing chamber air at a controlled flow rate to the gas analyzing system.</p> <p>Preliminary analysis of August to December 2018 data show that chamber-based flux estimates for O<sub>2</sub> and CO<sub>2</sub> were anti-correlated at all times, and that the O<sub>2</sub>:CO<sub>2</sub> molar exchange ratios (defined as ‑Δ[O<sub>2</sub>]/Δ[CO<sub>2</sub>]) varied considerably over time and between the different ecosystem compartments (soil, stems, and branches) with a median (interquartile range) of 0.94 (0.75 to 1.09).</p> <p>In system 2, CO<sub>2</sub>, O<sub>2</sub> and water vapor (H<sub>2</sub>O) measurements were performed with a fast response (5 Hz) gas analyzer using tunable infrared laser direct absorption spectroscopy (TILDAS, Aerodyne Research Inc., USA). We measured fluctuations in O<sub>2</sub>:CO<sub>2</sub> exchange ratios in air sampled at 1.5 times the canopy height, i.e. a typical eddy covariance set-up.</p> <p>Analysis of the high-frequency data revealed instrumental noise levels of ≈±12 ppm O<sub>2</sub>. Fourier transformation of high-frequency data obtained during well-mixed boundary layer conditions indicate that turbulent fluctuations of the O<sub>2</sub> signal were insufficiently resolved when compared to the CO<sub>2</sub> power spectra. When averaging high-frequency data to 2-min aggregates, instrumental noise was reduced to ≈±1 ppm, similar to the precision of system 1. At this timescale, contemporaneous measurements of above-canopy air revealed agreement between the fuel cell and the laser systems, both in O<sub>2</sub> mole fraction (R<sup>2</sup> = 0.6 slope = 0.7, MAE = 1.6 ppm) and in estimated O<sub>2</sub>:CO<sub>2</sub> exchange ratios of 1.01 and 0.97 for system 1 and 2, respectively.</p> <p>Our presentation will expand on the applicability of both O<sub>2</sub> and CO<sub>2 </sub>measurement systems with regard to micrometeorological flux techniques. Specifically, we elucidate on the potential of using O<sub>2 </sub>flux measurements as a constraint for estimating ecosystem-scale gross primary production.</p>

Research paper thumbnail of Standardisation of eddy-covariance flux measurements of methane and nitrous oxide

International Agrophysics

Commercially available fast-response analysers for methane (CH4) and nitrous oxide (N2O) have rec... more Commercially available fast-response analysers for methane (CH4) and nitrous oxide (N2O) have recently become more sensitive, more robust and easier to operate. This has made their application for long-term flux measurements with the eddy-covariance method more feasible. Unlike for carbon dioxide (CO2) and water vapour (H2O), there have so far been no guidelines on how to optimise and standardise the measurements. This paper reviews the state-of-the-art of the various steps of the measurements and discusses aspects such as instrument selection, setup and maintenance, data processing as well as the additional measurements needed to aid interpretation and gap-filling. It presents the methodological protocol for eddy covariance measurements of CH4 and N2O fluxes as agreed for the ecosystem station network of the pan-European Research Infrastructure Integrated Carbon Observation System and provides a first international standard that is suggested to be adopted more widely. Fluxes can be...

Research paper thumbnail of Uptake of gas-phase halogenated acetic acid molecules by water surfaces

The Journal of Physical Chemistry

ABSTRACT

Research paper thumbnail of Uptake of sulfur dioxide(G) by aqueous surfaces as a function of pH: the effect of chemical reaction at the interface

The Journal of Physical Chemistry

Research paper thumbnail of Uptake of gas-phase alcohol and organic acid molecules by water surfaces

The Journal of Physical Chemistry

It is now recognized that many important atmospheric reactions occur inside aqueous droplets of c... more It is now recognized that many important atmospheric reactions occur inside aqueous droplets of clouds and fogs. Recognition of the importance of these heterogeneous processes has stimulated an increasing amount of research in this area and a growing understanding about the nature of heterogeneous processes. Mass accommodation coefficients (α) have been measured as a function of temperature in the range

Research paper thumbnail of High-precision simultaneous 18O/16O, 13C/12C and 17O/16O analyses for µg-quantities of CaCO3 by tunable infrared laser absorption spectroscopy

Analytical Chemistry

Stable isotope ratios ((18)O/(16)O, (13)C/(12)C, and (17)O/(16)O) in carbonates have contributed ... more Stable isotope ratios ((18)O/(16)O, (13)C/(12)C, and (17)O/(16)O) in carbonates have contributed greatly to the understanding of Earth and planetary systems, climates, and history. The current method for measuring isotopologues of CO2 derived from CaCO3 is primarily gas-source isotope ratio mass spectroscopy (IRMS). However, IRMS has drawbacks, such as mass overlap by multiple CO2 isotopologues and contaminants, the requirement of careful sample purification, and the use of major instrumentation needing permanent installation and a high power electrical supply. Here, we report simultaneous (18)O/(16)O, (13)C/(12)C, and (17)O/(16)O analyses for microgram quantities of CaCO3 using a tunable mid-infrared laser absorption spectroscopy (TILDAS) system, which has no mass overlap problem and yields high sensitivity/precision measurements on small samples, as small as 0.02 μmol of CO2 (equivalent to 2 μg of CaCO3) with standard errors of less than 0.08 ‰ for (18)O/(16)O and (13)C/(12)C (±0.136 ‰ and ±0.387 ‰ repeatability; n = 10). In larger samples of CO2, 0.68 μmol (or 68 μg of CaCO3), standard error is less than 0.04 ‰ for (18)O/(16)O and (13)C/(12)C (< ±0.1 ‰ repeatability; n = 10) and 0.03 ‰ for (17)O/(16)O (±0.069 ‰ repeatability; n = 10). We also show, for the first time, the relationship between (17)O/(16)O ratios measured using the TILDAS system and published δ(17)O values of international standard materials (NBS-18 and -19) measured by IRMS. The benchtop TILDAS system, with cryogen-free sample preparation vacuum lines for microgram quantities of carbonates, is therefore a significant advance in carbonate stable isotope ratio geochemistry and is a new alternative to conventional IRMS.