Small Air Samples Research Articles

A GC-IRMS method for measuring sulfur isotope ratios of carbonyl sulfide from small air samples.

A new system was developed for measuring sulfur isotopes δ 33S and δ 34S from atmospheric carbonyl sulfide (COS) on small air samples of several liters, using pre-concentration and gas chromatography - isotope ratio mass spectrometry (GC-IRMS). Measurements of COS isotopes provide a tool for quantifying the COS budget, which will help towards better understanding climate feedback mechanisms. For a 4 liter sample at ambient COS mixing ratio, ~500 parts per trillion (ppt), we obtain a reproducibility error of 2.1 ‰ for δ 33S and 0.4 ‰ for δ 34S. After applying corrections, the uncertainty for an individual ambient air sample measurement is 2.5 ‰ for δ 33S and 0.9 ‰ for δ 34S. The ability to measure small samples allows application to a global-scale sampling program with limited logistical effort. To illustrate the application of this newly developed system, we present a timeseries of ambient air measurements, during the fall and winter of 2020 and 2021 in Utrecht, the Netherlands. The observed background values were δ 33S = 1.0 ± 3.4 ‰ and δ 34S = 15.5 ± 0.8 ‰ (VCDT). The maximum observed COS mixing ratios was only 620 ppt. This, in combination with the relatively high δ 34S suggests that the Netherlands receives little COS-containing anthropogenic emissions. We observed a change in COS mixing ratio and δ 34S with different air mass origin, as modelled with HYSPLIT backward trajectory analyses. An increase of 40 ppt in mean COS mixing ratio was observed between fall and winter, which is consistent with the expected seasonal cycle in the Netherlands. Additionally, we present the results of samples from a highway tunnel to characterize vehicle COS emissions and isotopic composition. The vehicle emissions were small, with COS/CO 2 being 0.4 ppt/ppm; the isotopic signatures are depleted relatively to background atmospheric COS.

A GC-IRMS method for measuring sulfur isotope ratios of carbonyl sulfide from small air samples

A new system was developed for measuring sulfur isotopes δ33S and δ34S from atmospheric carbonyl sulfide (COS or OCS) on small air samples of several liters, using a pre-concentration and gas chromatography – isotope ratio mass spectrometry (GC-IRMS) method. Measurements of COS isotopes provide a tool for quantifying the COS budget, which will help towards better understanding climate feedback mechanisms. For a 4 liter sample at ambient COS mixing ratio, ~500 parts per trillion (ppt), we obtain a reproducibility error of 2.1 ‰ for δ33S and 0.4 ‰ for δ34S. After applying corrections, the uncertainty for an individual ambient air sample measurement is 3.3 ‰ for δ33S and 0.9 ‰ for δ34S. The ability to measure small samples allows application to a global-scale sampling program with limited logistical effort. To illustrate the application of this newly developed system, we present a timeseries of ambient air measurements, during the fall and winter of 2020 and 2021 in Utrecht, the Netherlands. The observed background values were δ33S = 1.0 ± 3.4 ‰ and δ34S = 15.5 ± 0.8 ‰ (VCDT). The maximum observed COS mixing ratios was 620 ppt, suggesting that the Netherlands receives little COS-containing anthropogenic emissions. We observed a change in COS mixing ratio and sometimes also δ34S with different air mass origin, as modelled with the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) backward trajectory analyses. An increasing trend of 40 ppt was observed in the COS mixing ratio between fall and winter, which is consistent with the expected seasonal cycle in the Netherlands. Additionally, we present the results from samples taken inside a highway tunnel in Utrecht to characterize vehicle COS emissions and isotopic composition. The vehicle emissions were small, with a COS/CO2 ratio of 0.4 ppt/ppm; the isotopic signatures are depleted relatively to background atmospheric COS.

On the Inherent Variability of Particulate Matter Concentrations on Small Scales and the Consequences for Miniaturized Particle Sensors

Despite all the evident benefits of miniaturized particulate matter (PM) sensors, an inherent drawback exists in the uncertainty and validity of the measurement, which is closely related to the discrete nature of particulates suspended in air. The miniaturization of these devices not only leads to a smaller footprint for the devices themselves but also to a smaller volume of air being sampled. Even if a perfect measurement system is assumed, an uncertainty lies in assigning a supposedly representative particle concentration value to an environment due to the inherent variability of PM concentrations on small scales. This stems from the fact that particles are stochastically distributed in the air, leading to a non-uniform concentration for arbitrarily small volumes. Consequently, an uncertainty exists according to counting statistics, as the number of investigated particles in a small air sample is also low. Depending on the metric, the uncertainty may be augmented, as a small number of particles cannot accurately capture the distribution of particle sizes, especially since the size distribution extends over several orders of magnitude. This distribution related uncertainty is relevant for surface and mass related metrics in addition to the uncertainty resulting from counting statistics. We detected a minor impact from the distribution of the particle mass density, which contributes to the uncertainty for mass-related metrics, such as PM1, PM2.5 and PM10. We investigated the expected measurement uncertainty by analytical means and concluded that the distribution of particle sizes, the sample size and the ambient particle concentration significantly affect the measurement uncertainty for the range of conditions considered. To the best of our knowledge, this uncertainty has not been discussed in the current literature.

Analysis of low concentration reduced sulfur compounds (RSCs) in air: Storage issues and measurement by gas chromatography with sulfur chemiluminescence detection

Reduced sulfur compounds (RSCs) were measured at low concentrations in small volume air samples using a cryo-trapping inlet system and gas chromatograph outfitted with a sulfur chemiluminescence detector (GC-SCD). The relative sensitivity of the system to the RSCs follows the sequence H2S<CH3SH<OCS∼DMS<CS2. The analytical system achieves a detection limit of 120ppt in a 100mL air sample, which is suitable for measuring reactive RSCs (e.g., H2S and CH3SH) at ambient or near ambient atmospheric concentrations. The inlet system allows for replicate sampling from a stored air sample (sub-sampling), thereby improving estimates of instrumental precision and demonstrating the reproducibility of the analytical method. Although the SCD theoretically provides linear responses equivalent to the sulfur mass injected, we found that the response properties for each RSC differed. At concentrations below 2ppb, the compounds H2S and CH3SH have diminished responses, leading to larger measurement uncertainties. Two generations of commercially available SilcoCan canisters were tested to evaluate the relative RSC loss due to storage in the canister and loss of inertness because of coating age. The older generation canister (>6 years from initial coating) saw significant loss of H2S and CH3SH within 2 days, while the more recent generation canister (<1 year from initial coating) yielded percent recoveries of RSCs in the range of 85% (H2S and CH3SH) to 95% (OCS, DMS and CS2) after 7 days of storage, suggesting that these canisters may be suitable for the short-term storage of low level RSCs. The development of this low concentration, low sample volume method is well suited for measuring RSC gas fluxes from natural soils in laboratory incubations and in field flux chamber studies.

A new CF-IRMS system for quantifying stable isotopes of carbon monoxide from ice cores and small air samples

Abstract. We present a new analysis technique for stable isotope ratios (δ13C and δ18O) of atmospheric carbon monoxide (CO) from ice core samples. The technique is an online cryogenic vacuum extraction followed by continuous-flow isotope ratio mass spectrometry (CF-IRMS); it can also be used with small air samples. The CO extraction system includes two multi-loop cryogenic cleanup traps, a chemical oxidant for oxidation to CO2, a cryogenic collection trap, a cryofocusing unit, gas chromatography purification, and subsequent injection into a Finnigan Delta Plus IRMS. Analytical precision of 0.2‰ (±1δ) for δ13C and 0.6‰ (±1δ) for δ18O can be obtained for 100 mL (STP) air samples with CO mixing ratios ranging from 60 ppbv to 140 ppbv (~268–625 pmol CO). Six South Pole ice core samples from depths ranging from 133 m to 177 m were processed for CO isotope analysis after wet extraction. To our knowledge, this is the first measurement of stable isotopes of CO in ice core air.

“Cold” solid-phase microextraction method for the determination of volatile halocarbons present in the atmosphere at ultra-trace levels

Anthropogenic volatile halocarbons are compounds of great environmental concern because of their involvement in global change phenomena. They are present in the atmosphere at concentration levels in the order of parts per trillion by volume. The chosen analytical method for their determination is capillary gas chromatography coupled to mass spectrometry, preceded by an enrichment step on suitable adsorbent resins. The method here presented makes use of the solid-phase microextraction as a pre-analytical technique, using sub-ambient temperature in order to enhance the retention capability of the fiber coating. The proposed method was evaluated in terms of extraction efficiency, linearity, reproducibility, and limits of detection. Results obtained showed that trace atmospheric halocarbons are detectable even when enriching very small air sample volumes. A good chromatographic resolution is obtained as a consequence of the extremely low injection volume. Finally a standard GC–MS instrumentation equipped with a simple split-splitless injector was employed, thus avoiding the use of expensive dedicated apparatus. The method was also applied to the analysis of actual samples collected both in remote, and in semi-remote sites.

Boundary-layer isotope dilution/mass balance methods for measurement of nocturnal methane emissions from grazing sheep

Following advances with methods for 13C/ 12C isotopic analysis of methane in small (⩽4 L) air samples, new isotope dilution techniques are proposed for measurement of methane emissions at the paddock scale from grazing ruminant animals. These techniques combine measurement of the isotopic δ 13CH 4 composition of air samples with a non-intrusive mass balance method applied in the nocturnal boundary layer. Flux estimates from trials using the isotope dilution techniques are compared with estimates based on scaling up individual animal emission measurements using a rumen gas tracer technique. The methane flux assessed by the latter technique ranged from 35 to 70 mg (CH 4) m −2 d −1 with a stocking density between 10 and 20 sheep ha −1. The isotope dilution based nocturnal boundary-layer estimates generally agreed to better than a factor of 2 and usually to within 20% of the average of individual animal emission rate per unit area of paddock. Both static and advecting mass balance methods are developed. In the advecting case, the upwind/downwind contrast in δ 13C was typically 0.2–0.5‰. Care was necessary with air sampling to avoid error in this small contrast contributing to error in the flux. Agreement between concentration- and isotope-based nocturnal boundary layer methods and the sheep breath measurements indicated that sample representativeness was generally good. Factors which affect the accuracy of the method are examined and include variability in nocturnal mixing height, the assumed δ 13CH 4 composition of the source sheep breath and diurnal patterns in sheep emission. This paper establishes new techniques useful in the paddock to landscape scale although widespread application awaits further development of technology for rapid and repeatable field analysis of δ 13CH 4 in small samples.

Automated system for simultaneous analysis of delta(13)C, delta(18)O and CO(2) concentrations in small air samples.

In this paper we present an automated system for simultaneous measurement of CO(2) concentration, delta(13)C and delta(18)O from small (<1 mL) air samples in a short period of time (approximately 1 hour). This system combines continuous-flow isotope ratio mass spectrometry (CF-IRMS) and gas chromatography (GC) with an inlet system similar to conventional dual-inlet methods permitting several measurement cycles of standard and sample air. Analogous to the dual-inlet method, the precision of this system increases with the number of replicate cycles measured. The standard error of the mean for a measurement with this system is 0.7 ppm for the CO(2) concentration and 0.05 per thousand for the delta(13)C and delta(18)O with four replicate cycles and 0.4 ppm and 0.03 per thousand respectively with nine replicate cycles. The mean offset of our measurements from NOAA/CMDL analyzed air samples was 0.08 ppm for the CO(2) concentration, 0.01 per thousand for delta(13)C and 0.00 per thousand for delta(18)O. A specific list of the parts and operation of the system is detailed as well as some of the applications for micrometeorological and ecophysiological applications.

A new gas chromatograph‐isotope ratio mass spectrometry technique for high‐precision, N2O‐free analysis of δ13C and δ18O in atmospheric CO2 from small air samples

A new gas Chromatograph‐isotope ratio mass spectrometry (GC‐IRMS) technique for the first N2O‐free, high‐precision (&lt;0.05‰) isotopic analysis of δ13C and δ18O in atmospheric CO2 from small air samples has been developed. On‐line GC separation of CO2 and N2O from a whole air sample is combined with IRMS under elevated ion source pressures. A specialized open split interface is an integral part of the inlet system and ensures a continuous flow of either sample gas or pure helium to the IRMS. The analysis, including all flushing, uses a total amount of 45 mL of an air sample collected at ambient pressure. Of this, three 0.5 mL aliquots are injected onto the GC column, each providing ∼0.8 nmol CO2 in the IRMS source. At this sample size, δ13C precision obtained is at the theoretical shot noise limit. For typical ambient air samples collected in the Southern Hemisphere, demonstrated precisions for δ13C, δ18O, and the CO2 mixing ratio (all measured simultaneously) are 0.02‰, 0.04‰, and 0.4 ppm, parts per million (ppm) respectively. Since these data are achieved from small air samples without contamination by atmospheric N2O or the use of cryogen, the technique will be a valuable tool in global carbon cycle research.

CO(2) concentration measurements on air samples by mass spectrometry

A new technique for measuring CO(2) concentration in air samples, based on mass spectrometry, is described as an alternative to the common gas chromatographic method. Using a dual inlet isotope ratio mass spectrometer (IRMS), the ratio of the abundances of the m/z peaks 44 and 28 is determined. The precision of measurements (standard deviation <3 ppmv) is generally as good as the analysis with gas chromatography for small air samples (<1 ml STP of air). A major advantage of this new method is the possibility of parallel elemental and isotopic measurements of many air components. The technique is further improved by new wide mass range mass spectrometers allowing simultaneous intensity measurements of several m/z values between 28 and 44, resulting in an uncertainty of <0.5 ppm. The precision is somewhat limited by the production of N(2)O and NO(2) from N(2) and O(2) in the ion source, which accounts for about half of the signal strength at m/z 44. Copyright 2000 John Wiley & Sons, Ltd.

Simultaneous Determination of Volatile Metal (Pb, Hg, Sn, In, Ga) and Nonmetal Species (Se, P, As) in Different Atmospheres by Cryofocusing and Detection by ICPMS

A sensitive method for multielemental speciation analysis of volatile metal and metalloid compounds in air has been developed. The analytes are sampled simultaneously in the field by cryofocusing on a small glass wool-packed column at -175 °C. Detection is performed in the laboratory by low-temperature GC hyphenated with ICPMS. Oxygen addition in the carrier gas was used to reduce interferences originating from the presence of volatile carbon-containing species in the samples. Plasma stability during analysis was monitored continuously by internal standardization (Xe). This system provides routine absolute detection limits of 0.06-0.07 pg (as Pb) for tetraalkyllead species (Me(4)Pb, Et(4)Pb), 0.2 pg (as Sn) for tetraalkyltin species (Me(4)Sn, Et(4)Sn), 0.8 pg (as Hg) for mercury species (Hg(0), Me(2)Hg, Et(2)Hg), and 2.5 pg (as Se) for selenium species (Me(2)Se). This instrumentation makes it possible to collect small air sample volumes and has been successfully applied to the determination of volatile metal and metalloid species in the atmosphere in urban and rural locations. Qualitative application in the semiconductor industry is also reported with regard to the detection of arsenic (ASH(3), tert-butylarsine), phosphorus (PH(3), tert-butylphosphine), alkylindium, and gallium species.

Determination of Water Vapor in a Small Air Sample by a Nondispersive Infrared Gas Analyzer

A portable, nondispersive infrared (NDIR) gas analyzer was modified to measure the concentration of CO2 and water vapor in small gas samples. A 2-mL gas sample was taken from a series of sealed flasks partially filled with a saturated solution of chemicals known to produce various levels of relative humidity (RH). The modified NDIR instrument quantified water vapor content by its absorption at 2.59 μm. Peak height was displayed on a strip chart recorder and a standard curve constructed. At a specific temperature, the vapor pressure (VP) and vapor pressure difference (VPD) were calculated for sweet pepper (Capsicum annuum L., cv. Mazurka) fruit packed in trays that were covered with plastic films having several levels of perforations. Water loss from the fruit was highly correlated with VPD inside the packages. The modified NDIR instrument has an advantage over other instruments used to measure RH because it can rapidly and simultaneously determine the concentration of water vapor and CO2 in a single injection of a small gas sample.

PreCon: A Fully Automated Interface for the Pre-Gc Concentration of Trace Gases on Air for Isotopic Analysis

Abstract For the high precision isotope analysis of atmospheric trace gases a computer controlled concentration interface has been developed. From small air samples it collects either N2O or CO2 derived from CH4 at their respective concentrations (0.3 ppm for N2O, 1.7 ppm for CH4) into a small diameter cold trap (−196°C) and interfaces via GC and open split to an isotope ratio mass spectrometer (Finnigan MAT 252) for on-line isotope evaluation. External reproducibilities for repeated measurements of 100 ml air samples from the same source of < 0.2° (δ-notation) have been achieved for 13C/12C from CH4 and for 15N/14N and 18O/16O from N2O. The precision is adequate to monitor the isotopic changes in these gases during a day's course.

Odorous Sulfur Compounds Emitted during Production of Compost Used as a Substrate in Mushroom Cultivation

Large-scale composting facilities are known to cause environmental problems, mainly through pungent air emitted by composting material. In air samples taken above stacks set up to prepare compost used as a substrate in mushroom cultivation, several volatile compounds were identified by means of the coupled techniques of gas chromatography and mass spectrography. Among the compounds identified, sulfur-containing compounds [H(2)S, COS, CH(3)SH, CS(2), (CH(3))(2)S, (CH(3))(2)S(2), and (CH(3))(2)S(3)] are the most conspicuous in causing a nuisance. Quantification of these compounds was performed by concentrating a relatively small air sample on Tenax GC. The sampling method appeared to be very useful under field conditions. During the composting process, the concentration of the volatile sulfur compounds in emitted air ranged from 1 to 35 mumol/m. The highest concentrations were obtained at the end of the outdoor process. Total sulfur emission amounted to 8.3 mg of sulfur per kg (fresh weight) of compost. The end product still contained 2.58 g of sulfur per kg (fresh weight) of compost. Suggestions about the origin of the volatile sulfur compounds are made.

Determination of the Combined Nitrogen‐15 Content of Dinitrogen and Nitrous Oxide in Air

AbstractA method for measuring the total 15N content of an air sample containing 15N‐N2O and 15N‐N2 has been developed. A high voltage arcing process is used to rapidly decompose N2O into N2 and NOx, to randomly distribute the N isotopes between the N2 and NOx pools, and to fix a sample of N2 as NOx. A routine mass spectrometric 15N analysis based on the 29:28 ion signal ratio of either the N2 pool or the NOx sample after conversion to N2 will be equivalent to the 15N content of the original sample. Two methods of 15N analysis were shown to be equally accurate and precise. The air sample may be arced and the N2 analyzed by direct inlet into the mass spectrometer while cryogenically trapping the NOx, or the NOx may be reduced to an NH+4‐N salt that can be stored and analyzed later. If only a small air sample is available, 10 mL of air (at ambient pressure and temperature) can be mixed with ultrapure O2 to a N2/O2 ratio of 9:91 in a 90‐mL arc vessel and arced at atmospheric pressure for at least 150 s to produce sufficient NOx to yield 1 mg of fixed N for mass spectrometric analysis. The arc method measures the combined 15N content of the major gas species produced by denitrification by a single analysis and may be applicable for field studies.

Measurement of the emanation of radon-222 from danish soils

The radon-222 emanation from 70 samples of Danish soils, subsoils, and sedimentary rocks has been measured. Two methods have been employed. The first one is to follow the growth of the radon concentration in a radon-tight sample container by transferring small air samples to a scintillation flask detection system. The second one is to measure the equilibrium gamma-activities of lead-214 and bismuth-214 in the sample when the sample container is open and, subsequently, when it is closed. Based on the measured emanation rates the samples are grouped in three classes: 1) less than 5 atoms · sec −1 · kg −1, 2) from 5 to 10 atoms · sec −1 · kg −1, and 3) more than 10 atoms·sec −1. In class 3) some diatomitic clays have shown emanation rates as large as 100 atoms·sec −1·kg −1.

A fluorometric method for determining low concentrations of hydrogen sulphide in air

A fluorometric technique for the determination of low concentrations of hydrogen sulphide in air streams is described and possible limitations examined. The method is particularly suitable where accurate measurements of these low hydrogen sulphide concentrations are required in small air sample volumes. The reagent is a simple solution of fluorescein mercuric acetate (FMA—biochemical laboratory reagent grade), in dilute aqueous sodium hydroxide. Hydrogen sulphide reacts rapidly with the alkaline FMA solution, causing a quenching of fluorescence which is related in a definite way to the amount of hydrogen sulphide contained in the air stream. Reagent stability, overall precision and reproducibility of the method were found to be very satisfactory.

Simple methods for measuring and maintaining the proportion of carbon dioxide in air, for use in ecological studies of soil respiration

A group of technical procedures and devices are described which have proved useful in the study of the effects of carbon dioxide concentration on soil invertebrates and microbes. They include: (i) Methods for handling carbon dioxide-air mixtures. 1. (ii) Methods for measuring carbon dioxide concentration in small air samples. (A brief review of available techniques is followed by a description of a micro-electrolytic method using a plastic syringe and the construction and use of buried Polythene sacs for field use.) 2. (iii) Methods for maintaining carbon dioxide concentrations in small closed containers using carbon dioxide buffers.