N2O Data Research Articles

An alternative modelling approach to predict emissions of N2O and NO from forest soils

Emissions of N2O from forest soils in Europe are an important source of global greenhouse gas emissions. However, influencing the emission rates by forest management is difficult because the relations and feedbacks between forest and soils are complex. Process-based models covering both vegetation and soil biogeochemical processes are frequently used to analyse emission patterns. Particularly, the simulation of soil C and N turnover processes driving N2O production, consumption and emission from forest soils requires highly specific input data which renders their regional application difficult since at this scale, soil conditions are often not well understood. Therefore, a soil C and N model (DecoNit) has been developed which describes biogeochemical processes with a simplified structure compared to existing carbon/nitrogen models that nevertheless follows the basic physical and chemical laws involved and which allows to simulate N trace gas emissions. The DecoNit model was previously calibrated using an extensive dataset on decomposition rates of incubated plant materials, microbial dynamics and nitrification. The DecoNit model has now been embedded in a modular simulation environment (MoBiLE) where it is combined with soil water balance and forest process sub-modules. Here, we present the evaluation of MoBiLE-DecoNit with emission data of N2O and NO from forest soils of 15 European sites and compare simulation results with a previous study in which a more complex model (PnET-N-DNDC) was used. Evaluation criteria were as follows: (1) precision of modelled annual average emission rates; (2) coherence of modelled and measured annual average and daily emissions; (3) a dynamic representation of emission rates that correspond with the observed variance of fluxes. The results show that MoBiLE-DecoNit captures average annual emission rates more precisely than the more complex model PnET-N-DNDC. Also the structural underestimation of N trace gas fluxes from forest soils was resolved. Moreover, we present evidence that the new modelling approach is also somewhat more adequate for describing inter-daily emission dynamics. The combined MoBiLE-DecoNit is therefore thought to be a promising approach to simulate forest development and greenhouse gas balances on site and regional scales.

Effects of land use type and incubation temperature on greenhouse gas emissions from Chinese and Canadian soils

Land use type is an important factor influencing greenhouse gas emissions from soils, but the mechanisms involved in affecting potential greenhouse gas (GHG) emissions in different land use systems are poorly understood. Since the northern regions of Canada and China are characterized by cool growing seasons, GHG emissions under low temperatures are important for our understanding of how soil temperature affects soil C and N turnover processes and associated greenhouse gas emissions in cool temperate regions. Therefore, we investigated the effects of temperature on the emission of N2O, CO2, and CH4 from typical forest and grassland soils from China and Canada. The soils were incubated in the laboratory at 10°C and 15°C under aerobic conditions for 15 days. The results showed that land use type had a large impact on greenhouse gas emissions. The N2O emissions were significantly higher in grassland than in forest soils, while CO2 emissions were higher in forest than in grassland soils. Grassland soils were weak sources of CH4 emission, while forest soils were weak sinks of atmospheric CH4. The global warming potential of forest soils was significantly greater than that of grassland soils. Soil pH, C/N ratio, and soluble organic carbon concentrations and clay content were dominant factors influencing the emissions of N2O and CO2, respectively. Increasing temperature from 10°C to 15°C had no effects on CH4 flux, but significantly increased N2O emissions for all studied soils. The same pronounced effect was also found for CO2 emission from forest soils. Indications from this study are that the effects of land use type on the source–sink relationship and rates of GHG emissions should be taken into consideration when planning management strategies for mitigation of greenhouse gas emissions in the studied region, and temperature changes must be taken into account when scaling up point- or plot-based N2O and CO2 flux data to the landscape level due to large spatial and temporal variations of temperature that exist in the field. The reader is cautioned about the limitation with incubation studies on a limited number of samples/locations, and care need to be exercised to extrapolate the result to field conditions.

Transport coefficients and cross sections for electrons in N2O and N2O/N2 mixtures

A standard swarm analysis of electron scattering cross sections in nitrous oxide (N2O) is presented. The experimental results for drift velocities and effective ionization coefficients (differences between the ionization and attachment coefficients), obtained over an extended range of E/N (electric field normalized to the gas number density) by the pulsed-Townsend technique, are compared with the numerical solution of the Boltzmann equation. Our analysis shows that commonly used sets of cross sections have to be modified in order to fit the new experimental data, in particular the dissociative cross sections for attachment and electronic excitation (with a threshold energy of around 4.0 eV). Using a single set of cross sections it was possible to fit both the data for pure N2O and those for the N2O/N2 mixtures with 20%, 40%, 60% and 80% N2O.

MIPAS reduced spectral resolution UTLS-1 mode measurements of temperature, O<sub>3</sub>, HNO<sub>3</sub>, N<sub>2</sub>O, H<sub>2</sub>O and relative humidity over ice: retrievals and comparison to MLS

Abstract. During several periods since 2005 the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat has performed observations dedicated to the region of the upper troposphere/lower stratosphere (UTLS). For the duration of November/December 2005 global distributions of temperature and several trace gases from MIPAS UTLS-1 mode measurements have been retrieved using the IMK/IAA (Institut für Meteorologie und Klimaforschung/Instituto de Astrofísica de Andalucía) scientific processor. In the UTLS region a vertical resolution of 3 km for temperaure, 3 to 4 km for H2O, 2.5 to 3 km for O3, 3.5 km for HNO3 and 3.5 to 2.5 km for N2O has been achieved. The retrieved temperature, H2O, O3, HNO3, N2O, and relative humidity over ice are intercompared with the Microwave Limb Sounder (MLS/Aura) v2.2 data in the pressure range 316 to 0.68 hPa, 316 to 0.68 hPa, 215 to 0.68 hPa, 215 to 3.16 hPa, 100 to 1 hPa and 316 to 10 hPa, respectively. In general, MIPAS and MLS temperatures are biased within ±4 K over the whole pressure and latitude range. Systematic, latitude-independent differences of −2 to −4 K (MIPAS-MLS) at 121 hPa are explained by previously observed biases in the MLS v2.2 temperature retrievals. Temperature differences of −4 K up to 12 K above 10.0 hPa are present both in MIPAS and MLS with respect to ECMWF (European Centre for Medium-Range Weather Forecasts) and are likely due to deficiencies of the ECMWF analysis data. MIPAS and MLS stratospheric volume mixing ratios (vmr) of H2O are biased within ±1 ppmv, with indication of oscillations between 146 and 26 hPa in the MLS dataset. Tropical upper tropospheric values of relative humidity over ice measured by the two instruments differ by ±20% in the pressure range ~146 to 68 hPa. These differences are mainly caused by the MLS temperature biases. Ozone mixing ratios agree within 0.5 ppmv (10 to 20%) between 68 and 14 hPa. At pressures smaller than 10 hPa, MIPAS O3 vmr are higher than MLS by an average of 0.5 ppmv (10%). General agreement between MIPAS and MLS HNO3 is within the range of −1.0 (−10%) to 1.0 ppbv (20%). MIPAS HNO3 is 1.0 ppbv (10%) higher compared to MLS between 46 hPa and 10 hPa over the Northern Hemisphere. Over the tropics at 31.6 hPa MLS shows a low bias of more than 1 ppbv (>50%). In general, MIPAS and MLS N2O vmr agree within 20 to 40 ppbv (20 to 40%). Differences in the range between 100 to 21 hPa are attributed to a known 20% positive bias in MIPAS N2O data.

Supersaturated N2O in a perennially ice‐covered Antarctic lake: Molecular and stable isotopic evidence for a biogeochemical relict

The east lobe of Lake Bonney, a permanently ice‐covered lake in the McMurdo Dry Valleys, Antarctica, has a mid‐depth maximum N2O concentration of 43.3 [mol N L‐1 (>700,000% saturation with respect to air), representing one of the highest concentrations reported for a natural aquatic system. δ15N and δ18O measurements indicate that this is the most isotopically depleted N2O yet observed in a natural environment (minimum δ15N‐N2O of ‐79.6‰ vs. air‐N2; minimum δ18O‐N2O of ‐4.7‰ vs. Vienna standard mean ocean water), providing new end points for these parameters in natural systems. The extremely depleted nitrogen and oxygen isotopes, together with nitrogen isotopic isomer data for N2O, imply that most of the N2O was produced via incomplete nitrification and has undergone virtually no subsequent consumption. However, molecular evidence provides little support for metabolically active nitrifying populations at depths where the maximal N2O concentrations occur and contemporary biogeochemical reactions cannot explain the extreme excesses of N2O in Lake Bonney. The gas appears to be a legacy of past biogeochemical conditions within the lake, and in the absence of a significant sink and the presence of a highly stable water column, gradients in N2O produced by past microbial activity could persist in the cold saline waters of Lake Bonney for >104 years.

Stable isotope natural abundance of nitrous oxide emitted from Antarctic tundra soils: effects of sea animal excrement depositions

Nitrous oxide (N2O), a greenhouse gas, is mainly emitted from soils during the nitrification and denitrification processes. N2O stable isotope investigations can help to characterize the N2O sources and N2O production mechanisms. N2O isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of N2O emitted from Antarctic tundra ecosystems have been reported although the coastal ice-free tundra around Antarctic continent is the largest sea animal colony on the global scale. Here, we report for the first time stable isotope composition of N2O emitted from Antarctic sea animal colonies (including penguin, seal and skua colonies) and normal tundra soils using in situ field observations and laboratory incubations, and we have analyzed the effects of sea animal excrement depositions on stable isotope natural abundance of N2O. For all the field sites, the soil-emitted N2O was 15N- and 18O-depleted compared with N2O in local ambient air. The mean delta values of the soil-emitted N2O were delta15N = -13.5 +/- 3.2 per thousand and delta18O = 26.2 +/- 1.4 per thousand for the penguin colony, delta15N = -11.5 +/- 5.1 per thousand and delta18O = 26.4 +/- 3.5 per thousand for the skua colony and delta15N = -18.9 +/- 0.7 per thousand and delta18O = 28.8 +/- 1.3 per thousand for the seal colony. In the soil incubations, the isotopic composition of N2O was measured under N2 and under ambient air conditions. The soils incubated under the ambient air emitted very little N2O (2.93 microg N2O--N kg(-1)). Under N2 conditions, much more N2O was formed (9.74 microg N2O--N kg(-1)), and the mean delta15N and delta18O values of N2O were -19.1 +/- 8.0 per thousand and 21.3 +/- 4.3 per thousand, respectively, from penguin colony soils, and -17.0 +/- 4.2 per thousand and 20.6 +/- 3.5 per thousand, respectively, from seal colony soils. The data from in situ field observations and laboratory experiments point to denitrification as the predominant N2O source from Antarctic sea animal colonies.

Validation of ACE-FTS N<sub>2</sub>O measurements

Abstract. The Atmospheric Chemistry Experiment (ACE), also known as SCISAT, was launched on 12 August 2003, carrying two instruments that measure vertical profiles of atmospheric constituents using the solar occultation technique. One of these instruments, the ACE Fourier Transform Spectrometer (ACE-FTS), is measuring volume mixing ratio (VMR) profiles of nitrous oxide (N2O) from the upper troposphere to the lower mesosphere at a vertical resolution of about 3–4 km. In this study, the quality of the ACE-FTS version 2.2 N2O data is assessed through comparisons with coincident measurements made by other satellite, balloon-borne, aircraft, and ground-based instruments. These consist of vertical profile comparisons with the SMR, MLS, and MIPAS satellite instruments, multiple aircraft flights of ASUR, and single balloon flights of SPIRALE and FIRS-2, and partial column comparisons with a network of ground-based Fourier Transform InfraRed spectrometers (FTIRs). Between 6 and 30 km, the mean absolute differences for the satellite comparisons lie between −42 ppbv and +17 ppbv, with most within ±20 ppbv. This corresponds to relative deviations from the mean that are within ±15%, except for comparisons with MIPAS near 30 km, for which they are as large as 22.5%. Between 18 and 30 km, the mean absolute differences for the satellite comparisons are generally within ±10 ppbv. From 30 to 60 km, the mean absolute differences are within ±4 ppbv, and are mostly between −2 and +1 ppbv. Given the small N2O VMR in this region, the relative deviations from the mean are therefore large at these altitudes, with most suggesting a negative bias in the ACE-FTS data between 30 and 50 km. In the comparisons with the FTIRs, the mean relative differences between the ACE-FTS and FTIR partial columns (which cover a mean altitude range of 14 to 27 km) are within ±5.6% for eleven of the twelve contributing stations. This mean relative difference is negative at ten stations, suggesting a small negative bias in the ACE-FTS partial columns over the altitude regions compared. Excellent correlation (R=0.964) is observed between the ACE-FTS and FTIR partial columns, with a slope of 1.01 and an intercept of −0.20 on the line fitted to the data.

Solar occultation satellite data and derived meteorological products: Sampling issues and comparisons with Aura Microwave Limb Sounder

Derived Meteorological Products (DMPs, including potential temperature, potential vorticity (PV), equivalent latitude (EqL), horizontal winds and tropopause locations) from several meteorological analyses have been produced for the locations and times of measurements taken by several solar occultation instruments and the Aura Microwave Limb Sounder (MLS). MLS and solar occultation data are analyzed using DMPs to illustrate sampling issues that may affect interpretation and comparison of data sets with diverse sampling patterns and to provide guidance regarding the kinds of studies that benefit most from analyzing satellite data in relation to meteorological conditions using the DMPs. Using EqL or PV as a vortex‐centered coordinate does not alleviate all sampling problems, including those in studies using “vortex averages” of solar occultation data and in analyses of localized features (such as polar stratospheric clouds) and other fields that do not correlate well with PV. Using DMPs to view measurements with respect to their air mass characteristics is particularly valuable in studies of transport of long‐lived trace gases, polar processing in the winter lower stratosphere, and distributions and transport of O3 and other trace gases from the upper troposphere through the lower stratosphere. The comparisons shown here demonstrate good agreement between MLS and solar occultation data for O3, N2O, H2O, HNO3, and HCl; small biases are attributable to sampling effects or are consistent with detailed validation results presented elsewhere in this special section. The DMPs are valuable for many scientific studies and to facilitate validation of noncoincident measurements.

Validation of the Aura Microwave Limb Sounder middle atmosphere water vapor and nitrous oxide measurements

The quality of the version 2.2 (v2.2) middle atmosphere water vapor and nitrous oxide measurements from the Microwave Limb Sounder (MLS) on the Earth Observing System (EOS) Aura satellite is assessed. The impacts of the various sources of systematic error are estimated by a comprehensive set of retrieval simulations. Comparisons with correlative data sets from ground‐based, balloon and satellite platforms operating in the UV/visible, infrared and microwave regions of the spectrum are performed. Precision estimates are also validated, and recommendations are given on the data usage. The v2.2 H2O data have been improved over v1.5 by providing higher vertical resolution in the lower stratosphere and better precision above the stratopause. The single‐profile precision is ∼0.2–0.3 ppmv (4–9%), and the vertical resolution is ∼3–4 km in the stratosphere. The precision and vertical resolution become worse with increasing height above the stratopause. Over the pressure range 0.1–0.01 hPa the precision degrades from 0.4 to 1.1 ppmv (6–34%), and the vertical resolution degrades to ∼12–16 km. The accuracy is estimated to be 0.2–0.5 ppmv (4–11%) for the pressure range 68–0.01 hPa. The scientifically useful range of the H2O data is from 316 to 0.002 hPa, although only the 82–0.002 hPa pressure range is validated here. Substantial improvement has been achieved in the v2.2 N2O data over v1.5 by reducing a significant low bias in the stratosphere and eliminating unrealistically high biased mixing ratios in the polar regions. The single‐profile precision is ∼13–25 ppbv (7–38%), the vertical resolution is ∼4–6 km and the accuracy is estimated to be 3–70 ppbv (9–25%) for the pressure range 100–4.6 hPa. The scientifically useful range of the N2O data is from 100 to 1 hPa.

N2O emission from soil following combined application of fertiliser-N and ground weed residues

Emissions of N2O and CO2 were measured following combined applications of 15N-labelled fertiliser (100 μg N g−1; 10 atom % excess 15N) and organic olive crop weed residues (Avena sativa, Ononis viscosa, Ridolfia segetum and Olea europea; 100 μg N g−1) to a silt loam soil under controlled environment conditions. The objective was to determine the effect of varying combinations of inorganic fertiliser and plant residues on these emissions and soil mineral N dynamics. Emissions were generally increased following application of residues alone, with 23 ng N2O–N g−1 soil (2 ng N2O–N g−1 soil mg−1 biomass) and 389 μg CO2–C g−1 soil (39 μg CO2–C g−1 soil mg−1 biomass) emitted over 28 days after addition of the Ridolfia residues in the absence of fertiliser-N. N2O emissions from these residue-only treatments were strongly negatively correlated with residue lignin content (r = −0.91; P < 0.05), total carbon content (r = −0.90; P < 0.05) and (lignin + polyphenol)-to-N ratio (r = −0.70; P < 0.1). However, changes in the net input of these compounds through application of 25:75, 50:50 and 75:25 proportional mixtures of Avena and Ononis residues had no effect on emissions compared to their single (0:100 or 100:0) applications. Addition of fertiliser-N increased emissions (by up to 30 ng N2O–N g−1 28 days−1; 123%), particularly from the low residue-N treatments (Avena and Ridolfia) where a greater quantity of biomass was applied, resulting in emissions above that of the sum from the unfertilised residue and fertilised control treatments. In contrast, fertiliser application had no impact on emissions from the Olea treatment with the highest polyphenol (2%) and lignin (11%) contents due to strong immobilisation of soil N, and the 15N–N2O data indicated that residue quality had no effect on the denitrification of applied fertiliser-N. Such apparent inconsistencies mean that before the potential for manipulating N input (organic + inorganic) to lower gaseous N losses can be realised, first the nature and extent of interactions between the different N sources and any interactions with other compounds released from the residues need to be better understood.

Validation of the Improved Limb Atmospheric Spectrometer‐II (ILAS‐II) Version 1.4 nitrous oxide and methane profiles

This study assesses polar stratospheric nitrous oxide (N2O) and methane (CH4) data from the Improved Limb Atmospheric Spectrometer‐II (ILAS‐II) on board the Advanced Earth Observing Satellite‐II (ADEOS‐II) retrieved by the Version 1.4 retrieval algorithm. The data were measured between January and October 2003. Vertical profiles of ILAS‐II volume mixing ratio (VMR) data are compared with data from two balloon‐borne instruments, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS‐B) and the MkIV instrument, as well as with two satellite sensors, the Odin Sub‐Millimetre Radiometer (SMR) for N2O and the Halogen Occultation Experiment (HALOE) for CH4. Relative percentage differences between the ILAS‐II and balloon/satellite data and their median values are calculated in 10‐ppbv‐wide bins for N2O (from 0 to 400 ppbv) and in 0.05‐ppmv‐wide bins for CH4 (from 0 to 2 ppmv) in order to assess systematic differences between the ILAS‐II and balloon/satellite data. According to this study, the characteristics of the ILAS‐II Version 1.4 N2O and CH4 data differ between hemispheres. For ILAS‐II N2O VMR larger than 250 ppbv, the ILAS‐II N2O agrees with the balloon/SMR N2O within ±20% in both hemispheres. The ILAS‐II N2O in the VMR range from 30–50 to 250 ppbv (corresponding to altitudes of ∼17–30 km in the Northern Hemisphere (NH, mainly outside the polar vortex) and ∼13–21 km in the Southern Hemisphere (SH, mainly inside the polar vortex) is smaller by ∼10–30% than the balloon/SMR N2O. For ILAS‐II N2O VMR smaller than 30 ppbv (&gt;∼21 km) in the SH, the differences between the ILAS‐II and SMR N2O are within ±10 ppbv. For ILAS‐II CH4 VMR larger than 1 ppmv (&lt;∼25 km), the ILAS‐II CH4 agrees with the balloon/HALOE CH4 within ±5% in the NH. For ILAS‐II CH4 VMR larger than 0.3 ppmv in SH, the ILAS‐II CH4 is ∼9% larger than the HALOE CH4; note that this positive systematic difference between the ILAS‐II and HALOE CH4 has a seasonal dependence. Also note that the ILAS‐II N2O for its VMR smaller than 50 ppbv (&gt;∼30 km) and the ILAS‐II CH4 for its VMR smaller than 1 ppmv (&gt;∼25 km) only in the NH, are abnormally small compared to the balloon/satellite data.

Interpreting ancient ice in a shallow ice core from the South Yamato (Antarctica) blue ice area using flow modeling and compositional matching to deep ice cores

We explore methods of dating a 101 m ice core from a bare ice ablation area in the Yamato Mountains, Dronning Maud Land, East Antarctica. There are two unknowns, the age of the ice at the surface and the age spanned by the core. The ice crystal growth rate was used to estimate the age span of the core at about 5 kyr. CO2, CH4 and N2O data on the core were compared with well‐dated records from deep cores, leading to two plausible matches, both within isotope stage C. Detailed comparison of high‐resolution DEP records from this core and the Dome Fuji core support the 55–61 kyr BP fit best. Oxygen isotope values in the core were then used to constrain the source elevation of the snow in the core, and hence the velocities in a simple flow line model. We inverted the ice core surface age, age span and origin site and their confidence intervals in a sensitivity study of flow model parameter space. The flow line model predicts good matches to the core by reducing glacial flow rates to 70% of present‐day, accumulation rates by 45% with 10% confidence intervals. The modeled surface age for the whole meteorite field yields maximum surface ages of about 90 kyr, which is consistent with known, but poorly constrained, tephra dating, meteorite terrestrial ages and the frequency of meteorite discoveries. This approach can be used quite generally to link deep ice cores to surface outcrops on blue ice fields.

Long‐term changes of methane and hydrogen in the stratosphere in the period 1978–2003 and their impact on the abundance of stratospheric water vapor

The long‐term changes of the stratospheric mixing ratio of CH4 over the period of 1978–2003 are derived from balloon‐borne data of H2, CH4 and N2O. The data were obtained by collecting whole air samples and subsequent gas chromatographic analyses. To eliminate the short‐term variability attributed to dynamical processes, the N2O mixing ratio is used as a proxy for altitude. A correlation analysis for the individual years is applied and the CH4 mixing ratios are interpolated to four different levels of N2O, corresponding to altitudes of approximately 17, 23, 26 and 30 km at midlatitudes. For the investigated period of 1978 to 2003 we find increases at the four levels of 207 ± 32 ppb, 159 ± 21 ppb, 140 ± 34 ppb and 111 ± 60 ppb, respectively. The CH4 trend has slowed down in recent years and is best fitted by a second‐order polynomial. The increase of CH4 can account for only 25–34% of the increase in stratospheric H2O of 1%/yr over the last decades as derived from previous studies. The simultaneously measured time series of stratospheric H2 mixing ratios shows that the contribution of stratospheric H2 to the H2O trend in the period 1988–2003 is minor.

N2O, NH3 and NOx Emissions as a Function of Urea Granule Size and Soil Type Under Aerobic Conditions

We examined the influence of various urea granule sizes (<2, 7.0, 9.9 and 12.7 mm) applied into a silt loam soil (experiment 1) and soil types (sandy, silt and clay loam) treated with the largest granule (experiment 2) on gaseous N loss (except N2) at field capacity. The prilled urea (PU) was mixed into the soil whereas the urea granules were point-placed at a 5.0-cm depth. For experiment 1, N2O emission was enhanced with increasing granule size, ranging from 0.17-0.50% of the added N during the 45-day incubation period. In the case of experiment 2, the sandy loam soil (0.59%) behaved similarly with the silt loam (0.53%) but both showed remarkably lower emissions than were found for the clay loam soil (2.61%). Both nitrification and N2O emissions were delayed by several days with increasing granule size, and the latter was influenced by mineral N, soil water and pH. By contrast, the NH3 volatilization decreased with increasing granule size, implying the inhibition of urease activity by urea concentration gradients. Considering both experimental results, the NH3 loss was highest for the PU-treated (1.73%) and the larger granules regardless of soil type did not emit more than 0.27% of the added N over 22 days, possibly because the high concentrations of either mineral N or NH4 + in the soil surface layer (0-2.5 cm) and the high H + buffering capacity might regulate the NH3 emission. Similar to the pattern of NH3 loss, NOx emission was noticeably higher for the PU-treated soil (0.97%) than for the larger granule sizes (0.09-0.29%), which were the highest for the sandy and clay loam soils. Positional differences in the concentration of mineral N and nitrification also influenced the NOx emission. As such, total NH3 loss was proportional to total NOx emission, indicating similar influence of soil and environmental conditions on both. Pooled total N2O, NH3 and NOx emission data suggest that the PU-treated soil could induce greater gaseous N loss over larger urea granules, largely in the form of NH3 and NOx emissions, whereas a similar increase with the largest granule size was mainly due to the total N2O flux.

Probability Distribution and Spatial Dependence of Nitrous Oxide Emission

Climate controls soil N2O emissions via its effects on soil properties such as water‐filled pore space. Changes in climate should produce changes in the probability distribution and spatial dependency of soil N2O data. Knowing the extent of the changes in the distribution of this data is important for validating model predictions. The objectives of this study were to describe the probability distributions and estimate the spatial dependency of soil N2O emission data. On a hummocky, agricultural landscape in Saskatchewan, N2O emission data and related soil variables were taken from a 128‐point transect 15 times over 2 yr. Probability distributions were compared using a Chi‐square test. The range in spatial correlation was determined using the indicator semivariogram with a nested model fit approach. The mean N2O flux ranged from 25.3 to −0.2 ng N2O–N m−2s−1Probability distributions ranged in shape from reverse J‐shape through log normal to symmetrical. The majority of distributions were statistically different from each other, showing a lack of temporal stability. Mean N2O flux and distribution shape followed an event‐based/background emission pattern. High flux events had statistically similar, reverse J‐shaped distributions. As mean N2O flux decreased to a background level distribution, shape changed to log normal and symmetrical forms. A high nugget/sill ratio characterized the majority of sampling dates, although spatial dependency was generally moderate. Flux values in the fourth quartile tended to have a spatial dependency of 15 m, probably reflecting a topographic control at a landform element scale.

N2O and NO emissions from different N sources and under a range of soil water contents

Emissions of nitrous oxide (N2O) and nitric oxide (NO) have been identified as one of the most important sources of atmospheric pollution from grasslands. Soils are major sources for the production of N2O and NO, which are by-products or intermediate products of microbial nitrification and denitrification processes. Some studies have tried to evaluate the importance of denitrification or nitrification in the formation of N2O or NO but there are few that have considered emissions of both gases as affected by a wide range of different factors. In this study, the importance of a number of factors (soil moisture, fertiliser type and temperature) was determined for N2O and NO emissions. Nitrous oxide and NO evolution in time and the possibility of using the ratio NO:N2O as an indicator for the processes involved were also explored. Dinitrogen (N2) and ammonia (NH3) emissions were estimated and a mass balance for N fluxes was performed. Nitrous oxide and NO were produced by nitrification and denitrification in soils fertilised with \(\hbox{NH}_{4}^{+}\) and by denitrification in soils fertilised with \(\hbox{NO}_{3}^{-}\). Water content in the soil was the most important factor affecting N2O and NO emissions. Our N2O and NO data were fitted to quadratic (r=0.8) and negative exponential (r=0.7) equations, respectively. A long lag phase was observed for the N2O emitted from soils fertilised with \(\hbox{NO}_{3}^{-}\) (denitrification), which was not observed for the soils fertilised with \(\hbox{NH}_{4}^{+}\) (nitrification) and was possibly due to a greater inhibiting effect of low temperatures on microbial activity controlling denitrification rather than on nitrification. The use of the NO:N2O ratio as a possible indicator of denitrification or nitrification in the formation of N2O and NO was discounted for soils fertilised with \(\hbox{NO}_{3}^{-}\). The N mass balance indicated that about 50 kg N ha−1 was immobilised by microorganisms and/or taken up by plant roots, and that most of the losses ocurred in wet soils (WFPS >60%) as N2 and NH3 losses (>55%).

Nitrous oxide emissions from organic and conventional crop rotations in five European countries

Abstract Nitrous oxide (N2O) emissions from agriculture are currently estimated from N inputs using emission factors, and little is known about the importance of regional or management-related differences. This paper summarizes the results of a study in which N2O emission rates were recorded on 15–26 occasions during a 12-month period in organic and conventional dairy crop rotations in five European countries (Austria, Denmark, Finland, Italy, UK). A common methodology based on static chambers was used for N2O flux measurements, and N2O data were compiled together with information about N inputs (from fertilizers, N2 fixation, atmospheric deposition and excretal returns), crop rotations and soil properties. Organic rotations received only manure as N fertilizer, while manure accounted for 0–100% of fertilizer N in conventional rotations. A linear regression model was used to examine effects of location, system and crop category on N2O emissions, while a second model examined effects of soil properties. Nitrous oxide emissions were higher from conventional than from organic crop rotations except in Austria and, according to the statistical analysis, the differences between locations and crop categories were significant. Ammonium was significantly related to N2O emissions, although this effect was dominated by observations from a grazing system. Despite the limited number of samplings, annual emissions were estimated by interpolation. Across the two systems and five locations there was a significant relationship between total N inputs and N2O emissions at the crop rotation level which indicated that annually 1.6 ± 0.2% (mean ± standard error) of total N inputs were lost as N2O, while there was a background emission of 1.4 ± 0.3 kg N2O-N ha−1 year−1. Although this measurement program emphasized system effects at the expense of high temporal resolution, the results indicate that N input is a significant determinant for N2O emissions from agricultural soils.

Shipborne solar absorption measurements of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;, N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O and CO and comparison with SCIAMACHY WFM-DOAS retrievals

Abstract. CO, CH4, N2O and CO2 were retrieved from high resolution solar absorption spectra obtained during a ship cruise from Capetown to Bremerhaven in January/February 2003 by Fourier Transform Infrared (FTIR) spectroscopy. Precisions of better than 0.5% for the column averaged volume mixing ratios (VMR) of CH4 and CO2 are achieved using of O2 as a reference gas. Shipborne FTIR-measurements of CO and data from SCIAMACHY/ENVISAT retrieved by the Weighting Function Modified Differential Optical Absorption Spectroscopy (WFM-DOAS) retrieval algorithm show qualitatively the same latitudinal variations. WFM-DOAS data of CH4, N2O and CO2 measured over sea exhibit a great spread. The spread is significantly reduced for satellite measurements over land and a reasonable agreement can be obtained if the shipborne data are compared with the closest SCIAMACHY measurements over land. The number of comparisons is too small to draw conclusions. However, by including only WFM-DOAS data with small errors the shipborne and WFM-DOAS data compare within 5% for CH4 and CO2 and within 30% for N2O.

Mixing Processes during the Antarctic Vortex Split in September–October 2002 as Inferred from Source Gas and Ozone Distributions from ENVISAT–MIPAS

Abstract In late September 2002, an Antarctic major stratospheric warming occurred, which led to a strong distortion of the southern polar vortex and to a split of its mid- and upper-stratospheric parts. Such an event had never before been observed since the beginning of regular Antarctic stratospheric temperature observations in the 1950s. The split is studied by means of nonoperational level-2 CH4, N2O, CFC-11, and O3 data, retrieved at the Institute for Meteorology and Climate Research Karlsruhe (IMK) from high-resolution atmospheric limb emission spectra from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the European research satellite, Environmental Satellite (ENVISAT). Retrieved horizontal and vertical distributions of CH4 and N2O show good consistency with potential vorticity fields of the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis for the entire period under investigation, even for fine structures such as vortex filaments. Tracer correlation analysis suggests that mixing into the vortex had already occurred before the major warming and that vortex fragments were transported into the surrounding air masses on potential temperature levels above 400 K during the split. Correlation analysis of ozone with the source gases indicates slight ongoing ozone destruction in the lower-stratospheric vortex (below ∼500 K) after the beginning of the warming event.

Southern Ocean ventilation inferred from seasonal cycles of atmospheric N2O and O2/N2 at Cape Grim, Tasmania

The seasonal cycle of atmospheric N2O is derived from a 10-yr observational record at Cape Grim, Tasmania (41°S, 145°E). After correcting for thermal and stratospheric influences, the observed atmospheric seasonal cycle is consistent with the seasonal outgassing of microbially produced N2O from the Southern Ocean, as predicted by an ocean biogeochemistry model coupled to an atmospheric transport model (ATM). The model—observation comparison suggests a Southern Ocean N2O source of ~0.9 Tg N yr−1 and is the first study to reproduce observed atmospheric seasonal cycles in N2O using specified surface sources in forward ATM runs. However, these results are sensitive to the thermal and stratospheric corrections applied to the atmospheric N2O data. The correlation in subsurface waters between apparent oxygen utilization (AOU) and N2O production (approximated as the concentration in excess of atmospheric equilibrium ΔN2O) is exploited to infer the atmospheric seasonal cycle in O2/N2 due to ventilation of O2-depleted subsurface waters. Subtracting this cycle from the observed, thermally corrected seasonal cycle in atmospheric O2/N2 allows the residual O2/N2 signal from surface net community production to be inferred. Because N2O is only produced in subsurface ocean waters, where it is correlated to O2 consumption, atmospheric N2O observations provide a methodology for distinguishing the surface production and subsurface ventilation signals in atmospheric O2/N2, which have previously been inseparable.