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Shifting precipitation patterns due to climate change may impact peatland methane (CH4) emissions, as precipitation affects water table level which largely controls CH4 cycling. To investigate the impact of variable precipitation on peatland CH4 emissions, we measured CH4 fluxes and their 13C isotope composition (δ13C–CH4) across two summers marked by drought (2020) and heavy precipitation (2021) in a northern temperate poor fen in New Hampshire, USA. Monthly variation in CH4 fluxes and δ13C–CH4 was larger than interannual variation and variation between peatland microforms. While the seasonal pattern of CH4 emissions was not significantly different between years, the magnitude of seasonal changes in CH4 flux and δ13C–CH4 provided insight regarding the processes controlling CH4 emissions. Between July and August 2020, water table levels dropped > 15 cm, CH4 emissions decreased by an order of magnitude, and δ13C–CH4 increased ~ 10‰, suggesting lower water table levels promoted CH4 oxidation and reduced emissions in late summer. Rainstorms in July 2021 caused flooding and stimulated high CH4 emissions, but the impact of increased water table levels due to heavy precipitation on CH4 fluxes was transient and did not have an apparent effect on emitted δ13C–CH4. While drought conditions had a clear impact on CH4 fluxes and δ13C–CH4, our results suggest rainstorms and subsequent flooding do not have a sustained impact on CH4 emissions from temperate peatlands. [ABSTRACT FROM AUTHOR]

Water table depth and vegetation are key controls of methane (CH4) emissions from peatlands. Microtopography integrates these factors into features called microforms. Microforms often differ in CH4 emissions, but microform‐dependent patterns of belowground CH4 cycling remain less clearly resolved. To investigate the impact of microtopography on belowground CH4 cycling, we characterized depth profiles of the community composition and activity of CH4‐cycling microbes using 16S rRNA amplicon sequencing, incubations, and measurements of porewater CH4 concentration and isotopic composition from hummocks and lawns at Sallie's Fen in NH, USA. Geochemical proxies of methanogenesis and methanotrophy indicated that microforms differ in dominant microbial CH4 cycling processes. Hummocks, where water table depth is lower, had higher porewater redox potential (Eh) and higher porewater δ13C‐CH4 values in the upper 30 cm than lawns, where water table depth is closer to the peat surface. Porewater δ13C‐CH4 and δD‐CH3D values were highest at the surface of hummocks where the ratio of methanotrophs to methanogens was also greatest. These results suggest that belowground CH4 cycling in hummocks is more strongly regulated by methanotrophy, while in lawns methanogenesis is more dominant. We also investigated controls of porewater CH4 chemistry. The ratio of the relative abundance of methanotrophs to methanogens was the strongest predictor of porewater CH4 concentration and δ13C‐CH4, while vegetation composition had minimal influence. As microbial community composition was strongly influenced by redox conditions but not vegetation, we conclude that water table depth is a stronger control of belowground CH4 cycling across microforms than vegetation. Plain Language Summary: Northern peatlands are significant sources of the greenhouse gas methane (CH4) to the atmosphere. Patterns of CH4 emissions across peatlands often mirror patterns in water table level, vegetation cover, and elevation over small spatial scales as these factors influence microbial CH4 production and consumption. We investigated microbial CH4 production and consumption across areas in a northern peatland with varying water table depth and vegetation cover using measurements of belowground CH4 chemistry and microbial DNA sequencing. We observed consistent signals in the belowground concentration and stable isotope composition of CH4, which can indicate where different microbial processes are occurring, that suggest slightly elevated areas with lower water table depth are hotspots for CH4 consumption while CH4 production is more prominent in areas that are lower and wetter. Overall, both CH4 chemistry and microbial communities were more strongly influenced by changes in moisture than vegetation. These insights are important for understanding how climate change may impact CH4 cycling, as CH4 producing and consuming microbes respond differently to changes in temperature and moisture. Better understanding of the distribution of CH4 production and consumption across the landscape may also help scale predictions of CH4 emissions across larger areas for global modeling efforts. Key Points: Surface porewater δ13C‐CH4 and δD‐CH3D values were more reflective of methanotrophy in hummocks and methanogenesis in lawnsCommunity composition of methanogens and methanotrophs was influenced by redox conditions and water table level across microtopographyVegetation cover had limited influence on microbial community composition and porewater CH4 concentration and stable isotope composition [ABSTRACT FROM AUTHOR]

ABSTRACT We demonstrate the use of an aldehyde scrubber system to resolve isobaric aldehyde/alkene interferences in a proton transfer reaction mass spectrometer (PTR-MS) by selectively removing the aldehydes from the [...]

Gas concentrations and isotopic signatures can unveil microbial metabolisms and their responses to environmental changes in soil. Currently, few methods measure in situ soil trace gases such as the products of nitrogen and carbon cycling or volatile organic compounds (VOCs) that constrain microbial biochemical processes like nitrification, methanogenesis, respiration, and microbial communication. Versatile trace gas sampling systems that integrate soil probes with sensitive trace gas analyzers could fill this gap with in situ soil gas measurements that resolve spatial (centimeters) and temporal (minutes) patterns. We developed a system that integrates new porous and hydrophobic sintered polytetrafluoroethylene (sPTFE) diffusive soil gas probes that non-disruptively collect soil gas samples with a transfer system to direct gas from multiple probes to one or more central gas analyzer(s) such as laser and mass spectrometers. Here, we demonstrate the feasibility and versatility of this automated multiprobe system for soil gas measurements of isotopic ratios of nitrous oxide (δ18 O, δ15 N, and the 15 N site preference of N 2 O), methane, carbon dioxide (δ13 C), and VOCs. First, we used an inert silica matrix to challenge probe measurements under controlled gas conditions. By changing and controlling system flow parameters, including the probe flow rate, we optimized recovery of representative soil gas samples while reducing sampling artifacts on subsurface concentrations. Second, we used this system to provide a real-time window into the impact of environmental manipulation of irrigation and soil redox conditions on in situ N 2 O and VOC concentrations. Moreover, to reveal the dynamics in the stable isotope ratios of N 2 O (i.e., 14 N 14 N 16 O, 14 N 15 N 16 O, 15 N 14 N 16 O, and 14 N 14 N 18 O), we developed a new high-precision laser spectrometer with a reduced sample volume demand. Our integrated system – a tunable infrared laser direct absorption spectrometry (TILDAS) in parallel with Vocus proton transfer reaction mass spectrometry (PTR-MS), in line with sPTFE soil gas probes – successfully quantified isotopic signatures for N 2 O, CO 2 , and VOCs in real time as responses to changes in the dry–wetting cycle and redox conditions. Broadening the collection of trace gases that can be monitored in the subsurface is critical for monitoring biogeochemical cycles, ecosystem health, and management practices at scales relevant to the soil system. [ABSTRACT FROM AUTHOR]

A study was conducted to determine roles of soil bacteria in the uptake of methyl bromide in soils. A dilution system that can produce mixing ratios of methyl bromide and an analytical method were utilized. Results revealed that the varied soil moisture and temperature optima from different soils were caused by the diverse consumption activity of soil bacteria. However, soil fungi were not involved in the removal of methyl bromide from the soil.

Gas concentrations and isotopic signatures can unveil microbial metabolisms and their responses to environmental changes in soil. Currently, few methods measure soil trace gases such as the products of nitrogen and carbon cycling, or volatile organic compounds (VOCs), that could constrain microbial biochemical processes like nitrification, methanogenesis, respiration, and microbial communication. Versatile trace gas sampling systems that integrate soil probes with sensitive trace gas analyzers could fill this gap with measurements resolving spatial (centimeter scale) and temporal (minutes) variations in concentrations and isotopic signatures of in situ soil gases. We developed a system that integrates new 15 cm long sintered PTFE diffusive soil gas probes with various infrared spectrometers and a VOC mass spectrometer. The system is based on porous and hydrophobic soil probes that non-disruptively collect and transport gas from multiple probes to one or more central gas analyzers. Here, we demonstrate the feasibility and versatility of an automated multi-probe system for soil gas measurements of isotopic ratios of nitrous oxide (d18O, d15N, and the 15N site-preference of N2O), methane, carbon dioxide (d13C), and VOCs. First, we used an inert silica matrix to challenge probe measurements under controlled gas conditions. By changing and controlling system flow parameters, including probe flow rate, we optimized recovery of representative soil gas samples while reducing sampling artifacts on subsurface concentrations. Second, we forced environmental manipulations in soil-filled columns to demonstrate real time detection of subsurface gas dynamics in response to irrigation and soil redox conditions. In addition, we developed a new laser spectrometer to recover isotope ratios for 14N14N16O ("d446"), 14N15N16O ("d456"), 15N14N16O ("d546"), and 14N14N18O ("d448") with high precision and low concentration dependence. We captured temporal subsurface gas pulses in CO2, N2O, and VOCs. This demonstrated the potential for diffusive-based probes to couple to trace gas sensors for soil health and fertility studies, and to inform high-throughput meta-omics, leading to the development of a suite of powerful new tools for soil analysis. [ABSTRACT FROM AUTHOR]

We have developed a dual-beam tunable diode laser absorption spectroscopy system to follow the cocondensation of water and ethanol in a supersonic Laval nozzle. We determine the D2O monomer concentration in the vapor phase by fitting a Voigt profile to the measured line shape but had to develop a calibration scheme to evaluate the C2H5OD monomer concentration. To measure the temperature of the gas, we seed the flow with CH4 and measure two absorption lines with different lower state energies. These data give a far more detailed picture of binary condensation than axially resolved pressure measurements. In particular, we observe that the C2H5OD monomer starts to be depleted from the gas phase well before D2O begins to condense. [ABSTRACT FROM AUTHOR]

The NO(v,J)-fragment population distributions and recoil energies were measured for the vibrational predissociation of NO·HF following excitation of the H–F stretch. Most of the available energy appears in NO vibration and/or HF rotation. There is little recoil momentum. All NO(v,J) fragments are formed with near δ-function recoil kinetic energies, correlated with HF fragments in a single rotational level. Two dissociation channels proceed with similar probability to produce NO(v=0) and NO(v=1). Only two rotational levels of HF are populated. One of the HF rotational states is correlated exclusively with NO(v=0) fragments, the other is paired with NO(v=1) fragments. Constraints on fragment angular momenta as well as energetics appear important for the dissociation dynamics. The presence of significant amounts of vibrationally excited NO fragments, in the absence of observable spectroscopic perturbations, implies that intramolecular vibrational redistribution proceeds as the dimer dissociates. The data support two possibilities for the NO·HF dimer bond energy: (1) D0=448±5 cm-1 with coincident pairs of fragments NO(v=0)+HF(J=12) and NO(v=1)+HF(J=8); (2) D0=1769±10 cm-1 with JHF=9 and 2, respectively. [ABSTRACT FROM AUTHOR]

We have combined static pressure, spectroscopic temperature, Fourier transform infrared spectroscopy (FTIR), and small angle X-ray scattering (SAXS) measurements to develop a detailed picture of methanol condensing from a dilute vapor–carrier gas mixture under the highly supersaturated conditions present in a supersonic nozzle. In our experiments, methanol condensation can be divided into three stages as the gas mixture expands in the nozzle. In the first stage, as the temperature decreases rapidly, small methanol n-mers (clusters) form, increase in concentration, and evolve in size. In the second stage, the temperature decreases more slowly, and the n-mer concentrations continue to rise. Thermodynamic and FTIR experiments cannot, however, definitively establish if the average cluster size is constant or if it continues to increase. Finally, when the vapor becomes supersaturated enough, liquid droplets form vianucleation and growth, consuming more monomer and reducing the concentration of clusters. At the point where liquid first appears, cluster formation has already consumed up to 30% of the monomer. This is significantly more than is predicted by a model that describes the vapor phase as an equilibrium mixture of methanol monomer, dimer, and tetramer. An energy balance suggests that a significant fraction of the cluster population is larger than the tetramer, while preliminary SAXS measurements suggest that these clusters contain, on average, 6 monomers. [ABSTRACT FROM AUTHOR]

Better quantification of isotope ratios of atmosphere-ecosystem exchange of CO 2 could substantially improve our ability to probe underlying physiological and ecological mechanisms controlling ecosystem carbon exchange, but the ability to make long-term continuous measurements of isotope ratios of exchange fluxes has been limited by measurement difficulties. In particular, direct eddy covariance methods have not yet been used for measuring the isotopic composition of ecosystem fluxes. In this article, we explore the feasibility of such measurements by (a) proposing a general criterion for judging whether a sensor’s performance is sufficient for making such measurements (the criterion is met when the contribution of sensor error to the flux measurement error is comparable to or less than the contribution of meteorological noise inherently associated with turbulence flux measurements); (b) using data-based numerical simulations to quantify the level of sensor precision and stability required to meet this criterion for making direct eddy covariance measurements of the 13 C/ 12 C ratio of CO 2 fluxes above a specific ecosystem (a mid-latitude temperate forest in central Massachusetts, USA); (c) testing whether the performance of a new sensor—a prototype pulsed quantum cascade laser (QCL) based isotope-ratio absorption spectrometer (and plausible improvements thereon)—is sufficient for meeting the criterion in this ecosystem. We found that the error contribution from a prototype sensor (∼⃒0.2 ‰, 1 SD of 10 s integrations) to total isoflux measurement error was comparable to (1.5 to 2×) the irreducible ‘meteorological’ noise inherently associated with turbulent flux measurements above this ecosystem (daytime measurement error SD of ∼⃒60 % of flux versus meteorological noise of 30–40 % for instantaneous half-hour fluxes). Our analysis also shows that plausible instrument improvements (increase of sensor precision to ∼⃒0.1 ‰, 1 SD of 10 s integrations, and increased sensor stability during the half-hour needed to integrate eddy covariance measurements) should decrease the contribution of sensor error to the point where it is less than the contribution from meteorological noise. This suggests that new sensors using QCL-based isotope ratio absorption spectroscopy should make continuous long-term observations of the isotopic composition of CO 2 fluxes via eddy covariance methods feasible. [ABSTRACT FROM AUTHOR]

New diesel engine technologies and alternative fuel engines are being introduced into fleets of mass transit buses to try to meet stricter emission regulations of nitrogen oxides and particulates. Real-time instruments including an Aerodyne Research tunable infrared laser differential absorption spectrometer (TILDAS) were deployed in a mobile laboratory to assess the impact of the implementation of the new technologies on nitrogen oxide emissions in real world driving conditions. Using a "chase" vehicle sampling strategy, the mobile laboratory followed target vehicles, repeatedly sampling their exhaust. Nitrogen oxides from approximately 170 in-use New York City mass transit buses were sampled during the field campaigns. Emissions from conventional diesel buses, diesel buses with continuously regenerating technology (CRT), diesel hybrid electric buses, and compressed natural gas (CNG) buses were compared. The chase vehicle sampling method yields real world emissions that can be included in more realistic emission inventories. The NOx emissions from the diesel and CNG buses were comparable. The hybrid electric buses had approximately one-half the NOx emissions. In CRT diesels, NO2 accounts for about one-third of the NOx emitted in the exhaust while for non-CRT buses the NO2 fraction is less than 10%. [ABSTRACT FROM AUTHOR]

The Aerodyne Mobile Laboratory "chased" in-use curbside passenger buses operated by various operators in New York City. With the cooperation of New York State's Metropolitan Transit Authority, the relationships between the emissions of the several gas-phase species and particulate loadings were investigated across several bus technologies, bus types, and fuels (diesel, ultralow sulfur diesel, and compressed natural gas, CNG). The CNG buses followed did not employ an oxidation catalyst. The buses characterized were not prescreened in any fashion and were measured while deployed on their normal in-service routes. This paper focuses on the fuel-based mass emissions of SO2, H2CO, and CH4, measured using tunable infrared laser differential absorption spectroscopy. Sulfur dioxide emissions from buses known to be burning ultralow sulfur diesel (<30 ppmm 5) were 16 times lower than those from buses burning normal commercial diesel fuel, nominally less than 300 ppmm sulfur. Emissions of formaldehyde and methane from in-use CNG buses were ∼15 times greater than those from diesel powered buses. [ABSTRACT FROM AUTHOR]

In August 2001, the Aerodyne Mobile Laboratory simultaneously measured NO, NO2, and CO2 within 350 m of a taxiway and 550 m of a runway at John F. Kennedy Airport. The meteorological conditions were such that taxi and takeoff plumes from individual aircraft were clearly resolved against background levels. NO and NO2 concentrations were measured with 1 s time resolution using a dual tunable infrared laser differential absorption spectroscopy instrument, utilizing an astigmatic multipass Herriott cell. The CO2 measurements were also obtained at 1 s time resolution using a commercial non-dispersive infrared absorption instrument Plumes were measured from over 30 individual planes, ranging from turbo props to jumbo jets. NOx emission indices were determined by examining the correlation between NOx (NO + NO2) and CO2 during the plume measurements. Several aircraft tail numbers were unambiguously identified, allowing those specific airframe! engine combinations to be determined. The resulting NOx emission indices from positively identified in-service operating airplanes are compared with the published International Civil Aviation Organization engine certification test database collected on new engines in certification test cells. [ABSTRACT FROM AUTHOR]

Infrared line positions, linestrengths, and pressure-broadening coefficients are required to determine absolute trace gas concentrations from high-resolution absorption spectra. We have measured these values for the infrared absorption lines in the ν12 band (antisymmetric wag) of hydrazine between 965.4 and 965.7 cm−1 using a high-resolution tunable diode laser system with 0.0006 cm−1 spectral resolution and an 18-m path length multiple pass absorption cell. A continuous flow of hydrazine diluted to 100–500 parts per million in nitrogen at pressures between 0.1 and 50 Torr was used to prevent decomposition in the sampling cell. The total integrated linestrength from 965.477 to 965.663 cm−1 is (2.20±0.14)×10−20 cm2 molecule−1 cm−1. The strongest line in this region at 965.5557 cm−1 has a strength of 2.8×10−21 cm2 molecule−1 cm−1. The only isolated line in this region, at 965.4905 cm−1, has a broadening coefficient by nitrogen of 0.11±0.01 cm−1 atm−1 at 295 K. These results are compared to the qualitative high resolution spectra determined by other researchers using FTIR spectroscopy, and have been used to construct a HITRAN-format line list that can be used both to spectroscopically distinguish hydrazine from other components and to determine its concentration in a complex gas phase mixture. [Copyright &y& Elsevier]