Corelease of Genotoxic Polycyclic Aromatic Hydrocarbons and Nanoparticles from a Commercial Aircraft Jet Engine - Dependence on Fuel and Thrust.

Jet engines are important contributors to global CO2 emissions and release enormous numbers of ultrafine particles into different layers of the atmosphere. As a result, aviation emissions are affecting atmospheric chemistry and promote contrail and cloud formation with impacts on earth's radiative balance and climate. Furthermore, the corelease of nanoparticles together with carcinogenic polycyclic aromatic hydrocarbons (PAHs) affects air quality at airports. We studied exhausts of a widely used turbofan engine (CFM56-7B26) operated at five static thrust levels (idle, 7, 30, 65, and 85%) with conventional Jet A-1 fuel and a biofuel blend composed of hydro-processed esters and fatty acids (HEFA). The particles released, the chemical composition of condensable material, and the genotoxic potential of these exhausts were studied. At ground operation, particle number emissions of 3.5 and 0.5 × 1014 particles/kg fuel were observed with highest genotoxic potentials of 41300 and 8800 ng toxicity equivalents (TEQ)/kg fuel at idle and 7% thrust, respectively. Blending jet fuel with HEFA lowered PAH and particle emissions by 7-34% and 65-67% at idle and 7% thrust, respectively, indicating that the use of paraffin-rich biofuels is an effective measure to reduce the exposure of airport personnel to nanoparticles coated with genotoxic PAHs (Trojan horse effect).

Hydrologic Connectivity Regulates Riverine N2O Sources and Dynamics.

Indirect nitrous oxide (N2O) emissions from streams and rivers are a poorly constrained term in the global N2O budget. Current models of riverine N2O emissions place a strong focus on denitrification in groundwater and riverine environments as a dominant source of riverine N2O, but do not explicitly consider direct N2O input from terrestrial ecosystems. Here, we combine N2O isotope measurements and spatial stream network modeling to show that terrestrial-aquatic interactions, driven by changing hydrologic connectivity, control the sources and dynamics of riverine N2O in a mesoscale river network within the U.S. Corn Belt. We find that N2O produced from nitrification constituted a substantial fraction (i.e., >30%) of riverine N2O across the entire river network. The delivery of soil-produced N2O to streams was identified as a key mechanism for the high nitrification contribution and potentially accounted for more than 40% of the total riverine emission. This revealed large terrestrial N2O input implies an important climate-N2O feedback mechanism that may enhance riverine N2O emissions under a wetter and warmer climate. Inadequate representation of hydrologic connectivity in observations and modeling of riverine N2O emissions may result in significant underestimations.

CleanEx: A Versatile Automated Methane Preconcentration Device for High-Precision Analysis of 13CH4, 12CH3D, and 13CH3D.

The relative abundance of methane isotopologues offers key insights into the global methane (CH4) cycle. Advances in laser spectroscopy enable routine high-precision measurements even for rare deuterated methane isotopologues, 12CH3D and 13CH3D, provided there are sufficiently high methane amount fractions and reproducible measurement conditions, which can be achieved by CH4 adsorption-desorption techniques. We present a new cryogen-free automated preconcentration device─CleanEx─designed for quantitative extraction of CH4 from large volumes of sample gas and for cleaning by stepwise temperature-controlled desorption to separate interferant gases. We show that CleanEx has the capability to preconcentrate methane by almost 2000-fold from ∼18 L of air. The performance is demonstrated in a range of methane amount fractions between 2 ppm (µmol mol-1), which corresponds to the present-day ambient air, up to 1000 ppm, representative for close to source or process conditions. Advantages over existing devices are a significantly larger primary adsorption trap and a secondary cryo-focusing step, which ensures separation of methane from major atmospheric compounds, i.e., O2, Ar, and CO2. We have demonstrated quantitative extraction of methane, with no significant isotopic fractionation and high repeatability of 0.2‰, 0.6‰, and 0.8‰ (n = 42) for the studied isotopologue ratios, 13CH4/12CH4, 12CH3D/12CH4, and 13CH3D/12CH4, during cryogenic adsorption-desorption on HayeSep D material. The developed device in combination with a suitable laser spectrometer offers a robust and autonomous method for precise continuous monitoring of δ13C-CH4 and δD-CH4 in ambient air and optionally Δ13CH3D in process-derived methane.

Quantum cascade laser absorption spectrometer with a low temperature multipass cell for precision clumped CO2 measurement.

We present a quantum cascade laser-based absorption spectrometer deploying a compact (145 mL volume) segmented circular multipass cell (SC-MPC) with 6 m optical path length. This SC-MPC is embedded into an effective cooling system to facilitate operation at cryogenic temperatures. For CO2, the sample is cooled to 153 K, i.e. close to the sublimation point at 10 mbar. This enables efficient suppression of interfering hot-band transitions of the more abundant isotopic species and thereby enhances analytical precision. As a demonstration, the amount fractions of all three CO2 isotopologues involved in the kinetic isotope exchange reaction of 12C16O2 + 12C18O2⇌ 2·12C16O18O are measured. The precision in the ratios [12C18O2]/[12C16O2] and [12C16O18O]/[12C16O2] is 0.05 ‰ with 25 s integration time. In addition, we determine the variation of the equilibrium constant, K, of the above exchange reaction for carbon-dioxide samples equilibrated at 300 K and 1273 K, respectively.

Isotopically characterised N2 O reference materials for use as community standards.

RATIONALE: Information on the isotopic composition of nitrous oxide (N2 O) at natural abundance supports the identification of its source and sink processes. In recent years, a number of mass spectrometric and laser spectroscopic techniques have been developed and are increasingly used by the research community. Advances in this active research area, however, critically depend on the availability of suitable N2 O isotope Reference Materials (RMs). METHODS: Within the project Metrology for Stable Isotope Reference Standards (SIRS), seven pure N2 O isotope RMs have been developed and their 15 N/14 N, 18 O/16 O, 17 O/16 O ratios and 15 N site preference (SP) have been analysed by specialised laboratories against isotope reference materials. A particular focus was on the 15 N site-specific isotopic composition, as this measurand is both highly diagnostic for source appointment and challenging to analyse and link to existing scales. RESULTS: The established N2 O isotope RMs offer a wide spread in delta (δ) values: δ15 N: 0 to +104‰, δ18 O: +39 to +155‰, and δ15 NSP : -4 to +20‰. Conversion and uncertainty propagation of δ15 N and δ18 O to the Air-N2 and VSMOW scales, respectively, provides robust estimates for δ15 N(N2 O) and δ18 O(N2 O), with overall uncertainties of about 0.05‰ and 0.15‰, respectively. For δ15 NSP , an offset of >1.5‰ compared with earlier calibration approaches was detected, which should be revisited in the future. CONCLUSIONS: A set of seven N2 O isotope RMs anchored to the international isotope-ratio scales was developed that will promote the implementation of the recommended two-point calibration approach. Particularly, the availability of δ17 O data for N2 O RMs is expected to improve data quality/correction algorithms with respect to δ15 NSP and δ15 N analysis by mass spectrometry. We anticipate that the N2 O isotope RMs will enhance compatibility between laboratories and accelerate research progress in this emerging field.

Stable Isotope Analysis of Greenhouse Gases Requires Analyte Preconcentration.

Nitrous oxide (N2O) is an important trace gas contributing to global warming and depletion of ozone in the stratosphere. Its increasing abundance is caused mainly by anthropogenic sources, such as application of fertilizers in agriculture or emissions from industry. To understand the N2O global budget, its sources and sinks need to be well-described and quantified. In this project, a new method for N2O source appointment was developed that can help with this task. The method is based on analysis of the eight most abundant isotopic molecules of N2O, using quantum cascade laser absorption spectroscopy (QCLAS). The applicability of the method towards the N2O biogeochemical cycle was demonstrated on a prominent N2O source (bacterial denitrification) and the most important N2O sink (UV photolysis) on samples prepared in laboratory experiments. An extension of the QCLAS method to natural samples can be achieved by hyphenation with a preconcentration technique that increases concentration of the analyte and standardizes the sample matrix. This article provides an overview of currently applied preconcentration techniques in the field of greenhouse-gas analysis and a description of the preconcentration device TREX that will be employed in future projects with the developed QCLAS method.

First investigation and absolute calibration of clumped isotopes in N2 O by mid-infrared laser spectroscopy.

RATIONALE: Unravelling the biogeochemical cycle of the potent greenhouse gas nitrous oxide (N2 O) is an underdetermined problem in environmental sciences due to the multiple source and sink processes involved, which complicate mitigation of its emissions. Measuring the doubly isotopically substituted molecules (isotopocules) of N2 O can add new opportunities to fingerprint and constrain its cycle. METHODS: We present a laser spectroscopic technique to selectively and simultaneously measure the eight most abundant isotopocules of N2 O, including three doubly substituted species - so called "clumped isotopes". For the absolute quantification of individual isotopocule abundances, we propose a new calibration scheme that combines thermal equilibration of a working standard gas with a direct mole fraction-based approach. RESULTS: The method is validated for a large range of isotopic composition values by comparison with other established methods (laser spectroscopy using conventional isotopic scale and isotope ratio mass spectrometry). Direct intercomparison with recently developed ultrahigh-resolution mass spectrometry shows clearly the advantages of the new laser technique, especially with respect to site specificity of isotopic substitution in the N2 O molecule. CONCLUSIONS: Our study represents a new methodological basis for the measurements of both singly substituted and clumped N2 O isotopes. It has a high potential to stimulate future research in the N2 O community by establishing a new class of reservoir-insensitive tracers and molecular-scale insights.

What can we learn from N2 O isotope data? - Analytics, processes and modelling.

The isotopic composition of nitrous oxide (N2 O) provides useful information for evaluating N2 O sources and budgets. Due to the co-occurrence of multiple N2 O transformation pathways, it is, however, challenging to use isotopic information to quantify the contribution of distinct processes across variable spatiotemporal scales. Here, we present an overview of recent progress in N2 O isotopic studies and provide suggestions for future research, mainly focusing on: analytical techniques; production and consumption processes; and interpretation and modelling approaches. Comparing isotope-ratio mass spectrometry (IRMS) with laser absorption spectroscopy (LAS), we conclude that IRMS is a precise technique for laboratory analysis of N2 O isotopes, while LAS is more suitable for in situ/inline studies and offers advantages for site-specific analyses. When reviewing the link between the N2 O isotopic composition and underlying mechanisms/processes, we find that, at the molecular scale, the specific enzymes and mechanisms involved determine isotopic fractionation effects. In contrast, at plot-to-global scales, mixing of N2 O derived from different processes and their isotopic variability must be considered. We also find that dual isotope plots are effective for semi-quantitative attribution of co-occurring N2 O production and reduction processes. More recently, process-based N2 O isotopic models have been developed for natural abundance and 15 N-tracing studies, and have been shown to be effective, particularly for data with adequate temporal resolution. Despite the significant progress made over the last decade, there is still great need and potential for future work, including development of analytical techniques, reference materials and inter-laboratory comparisons, further exploration of N2 O formation and destruction mechanisms, more observations across scales, and design and validation of interpretation and modelling approaches. Synthesizing all these efforts, we are confident that the N2 O isotope community will continue to advance our understanding of N2 O transformation processes in all spheres of the Earth, and in turn to gain improved constraints on regional and global budgets.

Quantifying Isotopic Signatures of N2O Using Quantum Cascade Laser Absorption Spectroscopy.

Nitrous oxide, N2O, is the environmentally most relevant constituent of the biogeochemical nitrogen cycle. Human activities, e.g. the agricultural use of mineral fertilizers, accelerate nitrogen transformations, leading to higher emissions of this strong greenhouse gas. Investigating the stable isotopic composition of N2O provides a better understanding of formation mechanisms to disentangle its variable source and sink processes. Mid-infrared (mid-IR) laser spectroscopy is a highly attractive technique to analyze N2O isotopocules based on their specific ro-vibrational absorption characteristics. Specifically, quantum cascade laser absorption spectroscopy (QCLAS) in combination with preconcentration has shown to be powerful for simultaneous and high-precision analysis of the main N2O isotopocules. Recently, in the scope of my PhD project, we have been advancing this analytical technique for the analysis of the very rare doubly substituted N2O isotopic species 15N14N18O, 14N15N18O, and 15N15N16O, also known as clumped isotopes. Currently, we are investigating the potential of these novel isotopic tracers to track the complex N2O production and consumption pathways. Improved understanding of the nitrogen cycle will be a major step towards N2O emission reduction.

Preliminary assessment of stable nitrogen and oxygen isotopic composition of USGS51 and USGS52 nitrous oxide reference gases and perspectives on calibration needs.

RATIONALE: Despite a long history and growing interest in isotopic analyses of N2 O, there is a lack of isotopically characterized N2 O isotopic reference materials (standards) to enable normalization and reporting of isotope-delta values. Here we report the isotopic characterization of two pure N2 O gas reference materials, USGS51 and USGS52, which are now available for laboratory calibration (https://isotopes.usgs.gov/lab/referencematerials.html). METHODS: A total of 400 sealed borosilicate glass tubes of each N2 O reference gas were prepared from a single gas filling of a high vacuum line. We demonstrated isotopic homogeneity via dual-inlet isotope-ratio mass spectrometry. Isotopic analyses of these reference materials were obtained from eight laboratories to evaluate interlaboratory variation and provide preliminary isotopic characterization of their δ15 N, δ18 O, δ15 Nα , δ15 Nß and site preference (SP ) values. RESULTS: The isotopic homogeneity of both USGS51 and USGS52 was demonstrated by one-sigma standard deviations associated with the determinations of their δ15 N, δ18 O, δ15 Nα , δ15 Nß and SP values of 0.12 mUr or better. The one-sigma standard deviations of SP measurements of USGS51 and USGS52 reported by eight laboratories participating in the interlaboratory comparison were 1.27 and 1.78 mUr, respectively. CONCLUSIONS: The agreement of isotope-delta values obtained in the interlaboratory comparison was not sufficient to provide reliable accurate isotope measurement values for USGS51 and USGS52. We propose that provisional values for the isotopic composition of USGS51 and USGS52 determined at the Tokyo Institute of Technology can be adopted for normalizing and reporting sample data until further refinements are achieved through additional calibration efforts.

Effects of Four Prototype Gasoline Particle Filters (GPFs) on Nanoparticle and Genotoxic PAH Emissions of a Gasoline Direct Injection (GDI) Vehicle.

The fast replacement of traditional gasoline port-fuel injection technology with gasoline direct-injection (GDI) vehicles is expected to have a substantial impact on urban air quality. Herein we report on effects of four prototype gasoline particle filters (GPFs) on exhausts of a 1.6 L Euro-5 GDI vehicle. Two noncoated and two filters with catalytic coatings were investigated. These filters, on average, lowered PN emissions 4-7-fold to 4.0-6.8 × 1011 particles/km. Genotoxic PAHs were lowered 2-5-fold too with GPF-1-3, with GPF-1 having the highest efficiency, 79% and resulting in 45 ng toxic equivalent concentration (TEQ)/km. Thus, particle filtration efficiencies and reduction of the genotoxic potentials are correlated. GPF-4 showing the poorest particle filtration efficiency (66-78%) also released exhausts with highest genotoxic potential of 240-530 ng TEQ/km. We recently reported particle-number (PN) emissions of four generations of GDI vehicles (Euro-3 to Euro-6) which released, on average, 2.5 × 1012 ± 1.8 × 1012 particles/km exceeding the current European limit of 6.0 × 1011 particle/km. Thus, the implementation of filters to GDI vehicles requires best-available technology (BAT) with PN efficiencies >98% and catalytic activity, to avoid store-and-release of genotoxic PAHs. In-series applications of BAT-filters to GDI vehicles can lower genotoxic PAHs and soot nanoparticles.

Growth of Nitrosococcus-Related Ammonia Oxidizing Bacteria Coincides with Extremely Low pH Values in Wastewater with High Ammonia Content.

Ammonia oxidation decreases the pH in wastewaters where alkalinity is limited relative to total ammonia. The activity of ammonia oxidizing bacteria (AOB), however, typically decreases with pH and often ceases completely in slightly acidic wastewaters. Nevertheless, nitrification at low pH has been reported in reactors treating human urine, but it has been unclear which organisms are involved. In this study, we followed the population dynamics of ammonia oxidizing organisms and reactor performance in synthetic fully hydrolyzed urine as the pH decreased over time in response to a decrease in the loading rate. Populations of the ß-proteobacterial Nitrosomonas europaea lineage were abundant at the initial pH close to 6, but the growth of a possibly novel Nitrosococcus-related AOB genus decreased the pH to the new level of 2.2, challenging the perception that nitrification is inhibited entirely at low pH values, or governed exclusively by ß-proteobacterial AOB or archaea. With the pH shift, nitrite oxidizing bacteria were not further detected, but nitrous acid (HNO2) was still removed through chemical decomposition to nitric oxide (NO) and nitrate. The growth of acid-tolerant γ-proteobacterial AOB should be prevented, by keeping the pH above 5.4, which is a typical pH limit for the N. europaea lineage. Otherwise, the microbial community responsible for high-rate nitrification can be lost, and strong emissions of hazardous volatile nitrogen compounds such as NO are likely.

Reassessment of the NH4 NO3 thermal decomposition technique for calibration of the N2 O isotopic composition.

RATIONALE: In the last few years, the study of N2 O site-specific nitrogen isotope composition has been established as a powerful technique to disentangle N2 O emission pathways. This trend has been accelerated by significant analytical progress in the field of isotope ratio mass spectrometry (IRMS) and more recently quantum cascade laser absorption spectroscopy (QCLAS). METHODS: The ammonium nitrate (NH4 NO3 ) decomposition technique provides a strategy to scale the 15 N site-specific (SP ≡ Î´15 Nα - δ15 Nß ) and bulk (δ15 Nbulk  = (δ15 Nα  + Î´15 Nß )/2) isotopic composition of N2 O against the international standard for the 15 N/14 N isotope ratio (AIR-N2 ). Within the current project 15 N fractionation effects during thermal decomposition of NH4 NO3 on the N2 O site preference were studied using static and dynamic decomposition techniques. RESULTS: The validity of the NH4 NO3 decomposition technique to link NH4+ and NO3- moiety-specific δ15 N analysis by IRMS to the site-specific nitrogen isotopic composition of N2 O was confirmed. However, the accuracy of this approach for the calibration of δ15 Nα and δ15 Nß values was found to be limited by non-quantitative NH4 NO3 decomposition in combination with substantially different isotope enrichment factors for the conversion of the NO3- or NH4+ nitrogen atom into the α or ß position of the N2 O molecule. CONCLUSIONS: The study reveals that the completeness and reproducibility of the NH4 NO3 decomposition reaction currently confine the anchoring of N2 O site-specific isotopic composition to the international isotope ratio scale AIR-N2 . The authors suggest establishing a set of N2 O isotope reference materials with appropriate site-specific isotopic composition, as community standards, to improve inter-laboratory compatibility. Copyright © 2016 John Wiley & Sons, Ltd.

Bioethanol Blending Reduces Nanoparticle, PAH, and Alkyl- and Nitro-PAH Emissions and the Genotoxic Potential of Exhaust from a Gasoline Direct Injection Flex-Fuel Vehicle.

Bioethanol as an alternative fuel is widely used as a substitute for gasoline and also in gasoline direct injection (GDI) vehicles, which are quickly replacing traditional port-fuel injection (PFI) vehicles. Better fuel efficiency and increased engine power are reported advantages of GDI vehicles. However, increased emissions of soot-like nanoparticles are also associated with GDI technology with yet unknown health impacts. In this study, we compare emissions of a flex-fuel Euro-5 GDI vehicle operated with gasoline (E0) and two ethanol/gasoline blends (E10 and E85) under transient and steady driving conditions and report effects on particle, polycyclic aromatic hydrocarbon (PAH), and alkyl- and nitro-PAH emissions and assess their genotoxic potential. Particle number emissions when operating the vehicle in the hWLTC (hot started worldwide harmonized light-duty vehicle test cycle) with E10 and E85 were lowered by 97 and 96% compared with that of E0. CO emissions dropped by 81 and 87%, while CO2 emissions were reduced by 13 and 17%. Emissions of selected PAHs were lowered by 67-96% with E10 and by 82-96% with E85, and the genotoxic potentials dropped by 72 and 83%, respectively. Ethanol blending appears to reduce genotoxic emissions on this specific flex-fuel GDI vehicle; however, other GDI vehicle types should be analyzed.

Biofuel-Promoted Polychlorinated Dibenzodioxin/furan Formation in an Iron-Catalyzed Diesel Particle Filter.

Iron-catalyzed diesel particle filters (DPFs) are widely used for particle abatement. Active catalyst particles, so-called fuel-borne catalysts (FBCs), are formed in situ, in the engine, when combusting precursors, which were premixed with the fuel. The obtained iron oxide particles catalyze soot oxidation in filters. Iron-catalyzed DPFs are considered as safe with respect to their potential to form polychlorinated dibenzodioxins/furans (PCDD/Fs). We reported that a bimetallic potassium/iron FBC supported an intense PCDD/F formation in a DPF. Here, we discuss the impact of fatty acid methyl ester (FAME) biofuel on PCDD/F emissions. The iron-catalyzed DPF indeed supported a PCDD/F formation with biofuel but remained inactive with petroleum-derived diesel fuel. PCDD/F emissions (I-TEQ) increased 23-fold when comparing biofuel and diesel data. Emissions of 2,3,7,8-TCDD, the most toxic congener [toxicity equivalence factor (TEF) = 1.0], increased 90-fold, and those of 2,3,7,8-TCDF (TEF = 0.1) increased 170-fold. Congener patterns also changed, indicating a preferential formation of tetra- and penta-chlorodibenzofurans. Thus, an inactive iron-catalyzed DPF becomes active, supporting a PCDD/F formation, when operated with biofuel containing impurities of potassium. Alkali metals are inherent constituents of biofuels. According to the current European Union (EU) legislation, levels of 5 µg/g are accepted. We conclude that risks for a secondary PCDD/F formation in iron-catalyzed DPFs increase when combusting potassium-containing biofuels.

Interlaboratory assessment of nitrous oxide isotopomer analysis by isotope ratio mass spectrometry and laser spectroscopy: current status and perspectives.

RATIONALE: In recent years, research and applications of the N2O site-specific nitrogen isotope composition have advanced, reflecting awareness of the contribution of N2O to the anthropogenic greenhouse effect, and leading to significant progress in instrument development. Further dissemination of N2O isotopomer analysis, however, is hampered by a lack of internationally agreed gaseous N2O reference materials and an uncertain compatibility of different laboratories and analytical techniques. METHODS: In a first comparison approach, eleven laboratories were each provided with N2O at tropospheric mole fractions (target gas T) and two reference gases (REF1 and REF2). The laboratories analysed all gases, applying their specific analytical routines. Compatibility of laboratories was assessed based on N2O isotopocule data for T, REF1 and REF2. Results for T were then standardised using REF1 and REF2 to evaluate the potential of N2O reference materials for improving compatibility between laboratories. RESULTS: Compatibility between laboratories depended on the analytical technique: isotope ratio mass spectrometry (IRMS) results showed better compatibility for δ(15)N values, while the performance of laser spectroscopy was superior with respect to N2O site preference. This comparison, however, is restricted by the small number of participating laboratories applying laser spectroscopy. Offset and two-point calibration correction of the N2O isotopomer data significantly improved the consistency of position-dependent nitrogen isotope data while the effect on δ(15)N values was only minor. CONCLUSIONS: The study reveals that for future research on N2O isotopocules, standardisation against N2O reference material is essential to improve interlaboratory compatibility. For atmospheric monitoring activities, we suggest N2O in whole air as a unifying scale anchor.

Novel laser spectroscopic technique for continuous analysis of N2O isotopomers--application and intercomparison with isotope ratio mass spectrometry.

RATIONALE: Nitrous oxide (N(2)O), a highly climate-relevant trace gas, is mainly derived from microbial denitrification and nitrification processes in soils. Apportioning N(2)O to these source processes is a challenging task, but better understanding of the processes is required to improve mitigation strategies. The N(2)O site-specific (15)N signatures from denitrification and nitrification have been shown to be clearly different, making this signature a potential tool for N(2)O source identification. We have applied for the first time quantum cascade laser absorption spectroscopy (QCLAS) for the continuous analysis of the intramolecular (15)N distribution of soil-derived N(2)O and compared this with state-of-the-art isotope ratio mass spectrometry (IRMS). METHODS: Soil was amended with nitrate and sucrose and incubated in a laboratory setup. The N(2)O release was quantified by FTIR spectroscopy, while the N(2)O intramolecular (15)N distribution was continuously analyzed by online QCLAS at 1 Hz resolution. The QCLAS results on time-integrating flask samples were compared with those from the IRMS analysis. RESULTS: The analytical precision (2σ) of QCLAS was around 0.3‰ for the δ(15)N(bulk) and the (15)N site preference (SP) for 1-min average values. Comparing the two techniques on flask samples, excellent agreement (R(2)= 0.99; offset of 1.2‰) was observed for the δ(15)N(bulk) values while for the SP values the correlation was less good (R(2 )= 0.76; offset of 0.9‰), presumably due to the lower precision of the IRMS SP measurements. CONCLUSIONS: These findings validate QCLAS as a viable alternative technique with even higher precision than state-of-the-art IRMS. Thus, laser spectroscopy has the potential to contribute significantly to a better understanding of N turnover in soils, which is crucial for advancing strategies to mitigate emissions of this efficient greenhouse gas.

Isotope signatures of N2O in a mixed microbial population system: constraints on N2O producing pathways in wastewater treatment.

We present measurements of site preference (SP) and bulk (15)N/(14)N ratios (δ(15)N(bulk)(N2O)) of nitrous oxide (N(2)O) by quantum cascade laser absorption spectroscopy (QCLAS) as a powerful tool to investigate N(2)O production pathways in biological wastewater treatment. QCLAS enables high-precision N(2)O isotopomer analysis in real time. This allowed us to trace short-term fluctuations in SP and δ(15)N(bulk)(N2O) and, hence, microbial transformation pathways during individual batch experiments with activated sludge from a pilot-scale facility treating municipal wastewater. On the basis of previous work with microbial pure cultures, we demonstrate that N(2)O emitted during ammonia (NH(4)(+)) oxidation with a SP of -5.8 to 5.6 ‰ derives mostly from nitrite (NO(2)(-)) reduction (e.g., nitrifier denitrification), with a minor contribution from hydroxylamine (NH(2)OH) oxidation at the beginning of the experiments. SP of N(2)O produced under anoxic conditions was always positive (1.2 to 26.1 ‰), and SP values at the high end of this spectrum (24.9 to 26.1 ‰) are indicative of N(2)O reductase activity. The measured δ(15)N(bulk)(N2O) at the initiation of the NH(4)(+) oxidation experiments ranged between -42.3 and -57.6 ‰ (corresponding to a nitrogen isotope effect Δδ(15)N = δ(15)N(substrate) - δ(15)N(bulk)(N2O) of 43.5 to 58.8 ‰), which is considerably higher than under denitrifying conditions (δ(15)N(bulk)(N2O) 2.4 to -17 ‰; Δδ(15)N = 0.1 to 19.5 ‰). During the course of all NH(4)(+) oxidation and nitrate (NO(3)(-)) reduction experiments, δ(15)N(bulk)(N2O) increased significantly, indicating net (15)N enrichment in the dissolved inorganic nitrogen substrates (NH(4)(+), NO(3)(-)) and transfer into the N(2)O pool. The decrease in δ(15)N(bulk)(N2O) during NO(2)(-) and NH(2)OH oxidation experiments is best explained by inverse fractionation during the oxidation of NO(2)(-) to NO(3)(-).

Effect of diets with different crude protein levels on ammonia and greenhouse gas emissions from a naturally ventilated dairy housing.

Less crude protein (CP) in the diet can reduce nitrogen excretion of dairy cattle and lower their ammonia (NH3) and nitrous oxide (N2O) formation potential. The diet composition might also affect emissions of methane (CH4) and carbon dioxide (CO2). However, previous studies did not investigate the effect of diets with different CP levels that are customary practice in Switzerland on NH3 and greenhouse gas emissions on a practical scale. In a case-control approach, we quantified the emissions (NH3, N2O, CH4, CO2) in two separate but identical compartments of a naturally ventilated cubicle housing for lactating dairy cows over six days by using a tracer ratio method. Cows in one compartment received a diet with 116 g CP per kilogram dry matter (DM), in the other compartment with 166 g CP kg-1 DM. Subsequently, diets were switched for a second 6-day measurement phase. The results showed that the diet, aside from outside temperature and wind speed in the housing, was driving NH3 and N2O emissions. NH3 and N2O emission reduction per livestock unit (LU) was on average 46 % and almost 20 %, respectively, for the diet with low CP level compared to the higher CP level. In addition, strong relationships were observed between the CP content of the diet, N excretion in the urine and the milk urea content. An increased temperature or wind speed led to a clear increase in NH3 emissions. Differences in CH4 and CO2 emissions per LU indicated a significant influence of the diet, which cannot be attributed to the CP content. Our herd-level study demonstrated that a significant reduction in NH3 and N2O emissions related to LU, energy-corrected milk as well as DM intake can be achieved by lowering the CP content in the diet.