N2O Transport Research Articles

Temporal variation in nitrous oxide (N2O) fluxes from an oil palm plantation in Indonesia: An ecosystem‐scale analysis

AbstractThe rapidly growing areal extent of oil palm (Elaeis guineensis Jacq.) plantations and their high fertilizer input raises concerns about their role as substantial N2O sources. In this study, we present the first eddy covariance (EC) measurements of ecosystem‐scale N2O fluxes in an oil palm plantation and combine them with vented soil chamber measurements of point‐scale soil N2O fluxes. Based on EC measurements during the period August 2017 to April 2019, the studied oil palm plantation in the tropical lowlands of Jambi Province (Sumatra, Indonesia) is a high source of N2O, with average emission of 0.32 ± 0.003 g N2O‐N m−2 year−1 (149.85 ± 1.40 g CO2‐equivalent m−2 year−1). Compared to the EC‐based N2O flux, average chamber‐based soil N2O fluxes (0.16 ± 0.047 g N2O‐N m−2 year−1, 74.93 ± 23.41 g CO2‐equivalent m−2 year−1) are significantly (~49%, p < 0.05) lower, suggesting that important N2O pathways are not covered by the chamber measurements. Conventional chamber‐based N2O emission estimates from oil palm up‐scaled to ecosystem level might therefore be substantially underestimated. We show that the dynamic gas exchange of the oil palm canopy with the atmosphere and the oil palms' response to meteorological and soil conditions may play an important but yet widely unexplored role in the N2O budget of oil palm plantations. Diel pattern of N2O fluxes showed strong causal relationships with photosynthesis‐related variables, i.e. latent heat flux, incoming photosynthetically active radiation and gross primary productivity during day time, and ecosystem respiration and soil temperature during night time. At longer time scales (>2 days), soil temperature and water‐filled pore space gained importance on N2O flux variation. These results suggest a plant‐mediated N2O transport, providing important input for modelling approaches and strategies to mitigate the negative impact of N2O emissions from oil palm cultivation through appropriate site selection and management.

Land use drives nitrous oxide dynamics in estuaries on regional and global scales

AbstractUrban and agricultural development of coastal catchments is known to increase dissolved nitrogen inputs into estuaries; however, much less is known about how land use influences the production of the powerful greenhouse gas nitrous oxide (N2O). Here, we assess dissolved N2O dynamics in four nearby estuaries across a regional land use gradient and summarize the literature to put the observations into global perspective. During summer dry conditions, N2O saturation ranged from 131.4% ± 45.0% in the most pristine system (28% modified) to 198.6% ± 52.3% within the most modified urban system (91% modified). The N2O saturation in the wetter winter campaign was higher and more variable than the summer dry campaign (range 84.7–677.7%) likely due to direct transport of N2O into the estuaries from catchment runoff and/or produced through denitrification fueled by high nitrate inputs. During both seasons, N2O was lowest in areas adjacent to fringing mangroves and highest in upstream fresh/saltwater mixing areas. Coupling our results with previously published N2O data from 50 estuarine systems worldwide revealed that estuarine N2O increases concomitantly with catchment modification, dissolved inorganic nitrogen availability, and decreasing oxygen concentrations. Based on these results, a 1% increase in anthropogenic modification to global catchments (i.e., agricultural development and/or urbanization) may increase estuarine N2O saturation by 2.6% ± 1.2%. These findings indicate that future estuarine N2O emissions are likely to increase as anthropogenic modification of coastal catchments intensifies.

Effectiveness of plant growth regulators on emission reduction of greenhouse gas (Nitrous oxide): An approach for cleaner environment

Global climate change is one of the most prominent and complex environmental problems caused by increasing concentrations of atmospheric greenhouse gases. Rice paddies are an important anthropogenic source of nitrous oxide (N2O), a greenhouse gas approximately 298 times stronger than carbon dioxide. Identifying a suitable mitigation method for N2O emissions from rice agriculture, while maintaining optimum crop productivity is strongly needed. A 2-year field study was conducted on rice to assess N2O emissions in response to the application of different plant growth regulators (PGRs). The PGRs abscisic acid (ABA) and cytozyme (20 mg L−1), kinetin (10 and 20 mg L−1) and wet tea extract (1:20 w/w) along with distilled water as control were sprayed at the tillering and panicle initiation stages of rice. Compared with control treatment, exogenously applied ABA and kinetin (10 and 20 mg L−1) significantly (p < 0.01) reduced N2O emission primarily through regulation of leaf growth, stomatal frequency, and xylem vessel size of rice plants. Cytozyme and kinetin improved the grain yield through efficient photosynthesis. Leaf area index, tiller number, leaf photosynthesis, and transpiration were found to be directly associated (p < 0.05) with N2O emission. The PGRs regulated N2O transport by manipulating anatomical and physiological processes. Kinetin (10 mg L−1) application can be suitable for N2O emission reduction coupled with an increase in economic productivity. Considering the effect of N2O on global climate change, such mitigation measures may be effective for sustaining a cleaner environment for global community.

Effect of foliar application of plant growth regulators on nitrous oxide (N2O) emission and grain yield in wheat

Agricultural soils are the major source of global nitrous oxide (N2O) emission, and more than two thirds of N2O emission originate from soil. Recent studies have identified that green plants contribute to transport of N2O to the atmosphere. We investigated the effects of foliar application of plant growth regulators (PGRs) and growth stimulating chemicals on N2O emission and wheat grain yield for 2years. The PGRs' abscisic acid (ABA) and cytozyme (20mgL-1), kinetin (10 and 20mg L-1) and wet tea extract (1:20 w/w) along with distilled water as control were sprayed on wheat canopy at the tillering and panicle initiation stages. Our results showed that cytozyme and tea extract enhanced the plant dry biomass over control. Kinetin (10 and 20mgL-1) and cytozyme increased the plant photosynthetic rate and photosynthate partitioning towards the developing grain. ABA (20mgL-1) and kinetin (10 and 20mgL-1) reduced the N2O emission over control primarily through regulation of leaf growth, stomatal density and xylem vessel size. Leaf area, stomatal density and xylem vessel size were found to be associated with N2O transport and emission. We concluded that use of ABA and kinetin can reduce N2O emissions without any impact on wheat grain yield.

Mitigating N2O emissions from cropping systems after conversion from pasture − a modelling approach

Abstract Converting pasture to cropping is common in many of the world’s agricultural systems. This conversion results in substantial net mineralisation of soil organic matter that builds up during a phase of pasture. A few studies have shown that this mineralisation leads to increased nitrous oxide (N2O) emissions compared to long-term pasture or long-term cropping. Understanding of interactions leading to these significant emissions is still scarce but is needed to identify mitigation options for this situation. In this study, the Agricultural Production Systems sIMulator (APSIM) was used to investigate the optimal timing of pasture termination (relative to crop planting) and management of nitrogen (N) in crops after pasture termination to maximise crop yield and limit N2O emissions. Beforehand, APSIM’s performance in simulating yields and N2O emissions was tested against data from field experiments conducted in the temperate high-rainfall zone of southern Australia where N2O emissions were monitored with automatic gas collection chambers during the first year of cropping wheat after terminating long-term pasture on two adjacent sites in two consecutive years. Field experiments and simulation scenarios showed very high N2O emissions (up to 48 kg N2O-N ha−1 yr−1) in the first year of wheat after pasture termination, even without N fertiliser application. Measured cumulative N2O emissions, crop yields and soil mineral N and water content dynamics were simulated well with APSIM. Including a routine into APSIM to account for N2O transport through the soil profile improved the simulation of daily N2O emissions considerably, leading to up to 67% of the measured variability in daily N2O emissions being explained by the model. We predicted that a short fallow between termination of pasture and sowing wheat, instead of a long fallow which is the common practice, reduces N2O emissions by more than half in the first year of cropping without a noteworthy impact on crop yield. Reducing N fertiliser applications in the first few years after pasture termination by taking available soil mineral N into account, and applying the fertiliser six to twelve weeks after sowing instead of at sowing was predicted to further reduce N2O emissions. Since the model was calibrated against experimental data during the first year after pasture termination only, experiments determining N2O emissions in the first two or three years after terminating pasture are needed to confirm our predictions.

Effect of the soil water dynamics on nitrous oxide emissions

Microbial N2O production may occur via denitrification, a reaction which is influenced by the soil's water content. This study aimed to test the effect of soil water dynamics on N2O production and transport. The treatments consisted of two levels of soil bulk density (BD), negative pressure head applied on the soil cylinder (H), and saturated hydraulic conductivity of the ceramic plate placed at the bottom of the soil sample (K). We controlled the water status of repacked soil samples during two wetting-drying cycles, by using a multistep outflow system. The matric potential, outflow, N2O, and CO2 fluxes were recorded over time. A brief N2O peak occurred at the beginning of soil drying: N2O produced and entrapped in the soil during the wetting phase was released during soil drying with the increase in soil gas diffusion. Similar peaks dynamics were observed for CO2, implying that a physical process was involved. A relationship was observed to occur with maximum N2O fluxes increasing exponentially with cumulative drainage. Indeed, during drying, high N2O fluxes were measured when the air-entry potential was reached, i.e., when gas pathways were available for fast N2O transport in the gas phase. Then, maximum and cumulative N2O fluxes were highest for low BD and fast water flow during drying. Samples with the highest BD had smaller pore sizes, leading to low outflows at a given negative pressure head, and giving more time for further reduction of N2O to N2. We ranked the importance of the parameters controlling cumulative N2O fluxes: H>BD>K.

Factors controlling methane and nitrous-oxide variability in the southern British Columbia coastal upwelling system

Coastal upwelling systems are important marine sources of methane (CH4) and nitrous-oxide (N2O). Current understanding of the controls on CH4 and N2O distributions in these coastal waters is restricted by limited data availability. We present the first multi-year measurements of CH4 and N2O distributions from the seasonally upwelling shelf waters of British Columbia, Canada, a coastal end-member of the north Pacific oxygen minimum zone (OMZ). Our data show significant seasonal differences in CH4 and N2O distributions and fluxes driven predominantly by upwelling. Methane is supplied to the water column primarily from sediments (especially near methane seeps), and is transported to the surface mixed layer by upwelling. A positive correlation between CH4 concentrations and salinity indicates limited inputs from Fraser River estuary waters to the study site. Shelf waters receive N2O from a deep, off-shelf N2O maximum in the OMZ core, and from nitrification in the water column and possibly sediments. Both the physical transport of N2O and its apparent in situ production are enhanced under upwelling conditions. N2O yields from nitrification, estimated from changes in N2O and nitrate+nitrite (NO3−+NO2−) along isopycnals, ranged from 0.04–0.49%, with the highest values observed under low ambient O2 concentrations. Sea–air fluxes ranged from −4.5–21.9μmolm−2day−1 for N2O and 2.5–34.1μmolm−2day−1 for CH4, with the highest surface fluxes observed following summer upwelling over the broad continental shelf of southern Vancouver Island. Our results provide new insight into the factors driving spatial and inter-annual variability in marine CH4 and N2O in high productivity coastal upwelling regions. Continued time-series measurements will be invaluable in understanding the longer-term impacts of climate-driven variability on marine biogeochemical cycles in these dynamic near-shore waters.

Projections of oceanic N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O emissions in the 21st century using the IPSL Earth system model

Abstract. The ocean is a substantial source of nitrous oxide (N2O) to the atmosphere, but little is known about how this flux might change in the future. Here, we investigate the potential evolution of marine N2O emissions in the 21st century in response to anthropogenic climate change using the global ocean biogeochemical model NEMO-PISCES. Assuming nitrification as the dominant N2O formation pathway, we implemented two different parameterizations of N2O production which differ primarily under low-oxygen (O2) conditions. When forced with output from a climate model simulation run under the business-as-usual high-CO2 concentration scenario (RCP8.5), our simulations suggest a decrease of 4 to 12 % in N2O emissions from 2005 to 2100, i.e., a reduction from 4.03/3.71 to 3.54/3.56 TgN yr−1 depending on the parameterization. The emissions decrease strongly in the western basins of the Pacific and Atlantic oceans, while they tend to increase above the oxygen minimum zones (OMZs), i.e., in the eastern tropical Pacific and in the northern Indian Ocean. The reduction in N2O emissions is caused on the one hand by weakened nitrification as a consequence of reduced primary and export production, and on the other hand by stronger vertical stratification, which reduces the transport of N2O from the ocean interior to the ocean surface. The higher emissions over the OMZ are linked to an expansion of these zones under global warming, which leads to increased N2O production, associated primarily with denitrification. While there are many uncertainties in the relative contribution and changes in the N2O production pathways, the increasing storage seems unequivocal and determines largely the decrease in N2O emissions in the future. From the perspective of a global climate system, the averaged feedback strength associated with the projected decrease in oceanic N2O emissions amounts to around −0.009 W m−2 K−1, which is comparable to the potential increase from terrestrial N2O sources. However, the assessment for a potential balance between the terrestrial and marine feedbacks calls for an improved representation of N2O production terms in fully coupled next-generation Earth system models.

Emissions of nitrous oxide from the leaves of grasses

Nitrous oxide (N2O) emissions from pastoral agriculture are considered to originate from the soil as a consequence of microbial activity during soil nitrification and denitrification. However, recent studies have identified the plant canopy as a potentially significant source of N2O emissions to the atmosphere. Understanding the extent and mechanisms of plant emissions may provide new mitigation opportunities as current options only target soil microbial processes. We developed an experimental apparatus and protocol to partition N2O emissions between the leaves of grasses and the soil and measured emissions from ten common grass species found in New Zealand pastures. The chamber design enabled us to identify measurable changes in N2O concentration over a period of 1 h and to distinguish a range of emissions from 0.001 to 0.25 mg N2O-N/m2 leaf area/h. There was a 10-fold variation among species; Holcus lanataus, Lolium perenne and Paspalum dilatatum had the highest leaf N2O emissions and Poa annua the lowest. Grasses do emit N2O from their leaves and the rate that this occurs varies among grass species. The emission does not appear to arise from formation of N2O in plant leaves but more likely reflects transport of N2O from the soil. Differences in emission rates appear to arise from a plant influence on the rate of formation of N2O in the soil rather than the rate of transportation through the plant.

Inundation strongly stimulates nitrous oxide emissions from stems of the upland tree Fagus sylvatica and the riparian tree Alnus glutinosa

Nitrous oxide (N2O) and methane (CH4) can be emitted from surfaces of riparian plants. Data on the emission of these greenhouse gases by upland trees are scarce. We quantified CH4 and N2O emissions from stems of Fagus sylvatica, an upland tree, and Alnus glutinosa, a riparian tree. The gas fluxes were investigated in mesocosms under non-flooded control conditions and during a flooding period using static chamber systems and gas chromatographic analyses. Despite differences in the presence of an aerenchyma system, both tree species emitted N2O and CH4 from the stems. Flooding caused a dramatic transient increase of N2O stem emissions by factors of 740 (A. glutinosa) and even 14,230 (F. sylvatica). Stem emissions of CH4 were low and even deposition was determined (F. sylvatica controls). The results suggest that CH4 was transported mainly through the aerenchyma, whereas N2O transport occurred in the xylem sap. For the first time it has been demonstrated that upland trees such as F. sylvatica clearly significantly emit N2O from their stems despite lacking an aerenchyma. If this result is confirmed in adult trees, upland forests may constitute a new and significant source of atmospheric N2O.

Plant morphophysiological and anatomical factors associated with nitrous oxide flux from wheat (Triticum aestivum)

Experiments were conducted to study the dynamics of nitrous oxide (N₂O) emission from wheat varieties viz., Sonalika, HUW 468, HUW 234 and DBW 14 grown in alluvial soils of North Bank Plain Agroclimatic Zone of Assam, India. Attempts were made to find out the relationship of N₂O emission with plant morphophysiological, anatomical and soil properties. N₂O fluxes from wheat varieties ranged from 40 μg N₂O-N m⁻² h⁻¹ to 295 μg N₂O-N m⁻² h⁻¹. Soil organic carbon and soil temperature have shown significant relationship with N₂O flux. The rate of leaf transpiration recorded from the wheat varieties at different growth stages exhibited a positive correlation with N₂O emission suggesting that movement of N₂O along with the transpirational water flow may be an important mechanism of N₂O transport and emission through wheat plants. Anatomical investigation by scanning electron microscope revealed that N₂O emission has relationship with stomatal frequency of leaf and leaf sheaths. Variety HUW 234 with the highest stomatal frequency of leaf and leaf sheath also recorded higher seasonal N₂O emission compared to other varieties. Seasonal N₂O emission (E(sif)) of the varieties ranged from 3.25 to 3.81 kg N₂O-N ha⁻¹. Significant variations in E(sif) values were recorded within the varieties.

Assessment of German nitrous oxide emissions using empirical modelling approaches

Direct nitrous oxide (N2O) emissions from agricultural soils contribute considerably to anthropogenic GHG emissions. Albeit a key source of emissions in many countries, direct N2O emissions are still calculated and reported to the United Nations Convention on Climate Change using default emission factors defined in the IPCC guidelines (IPCC 1996, 2006). It is known that processes controlling production and transport of N2O are highly sensitive to environmental conditions defined by weather, soil and management. The accuracy of N2O emission budgets and the efficiency of mitigation can be improved if those dependencies are considered with regionalized emission factors. In this study an empirical method originating from soft computing techniques based on measured data is developed and applied to quantify direct N2O emissions from agricultural soils at field and national level in Germany between 1990 and 2005. The method is used to derive maps of emission factor distribution of direct N2O emissions of agricultural land in Germany. Model results are compared with alternative empirical approaches from literature. Results from developing empirical models show that grassland and cropland have to be differentiated according to the key controls driving N2O emissions. N2O emissions of German croplands are highly influenced by climatic conditions and soil properties. The variability of N2O fluxes on grasslands is mainly driven by the fertilizer N applied. The model comparison using measured European N2O emissions exhibits profound discrepancies between the models used on a regional scale. The nationwide budgets derived span a narrow range of −8 to 28% relative to direct N2O emissions quantified by the German national inventory report. The emission factor of German agriculture estimated by the developed model is 0.91% of fertilizer N applied.

Temporal trends in N2O flux dynamics in a Danish wetland – effects of plant‐mediated gas transport of N2O and O2 following changes in water level and soil mineral‐N availability

AbstractTemporal trends of N2O fluxes across the soil–atmosphere interface were determined using continuous flux chamber measurements over an entire growing season of a subsurface aerating macrophyte (Phalaris arundinacea) in a nonmanaged Danish wetland. Observed N2O fluxes were linked to changes in subsurface N2O and O2 concentrations, water level (WL), light intensity as well as mineral‐N availability. Weekly concentration profiles showed that seasonal variations in N2O concentrations were directly linked to the position of the WL and O2 availability at the capillary fringe above the WL. N2O flux measurements showed surprisingly high temporal variability with marked changes in fluxes and shifts in flux directions from net source to net sink within hours associated with changing light conditions. Systematic diurnal shifts between net N2O emission during day time and deposition during night time were observed when max subsurface N2O concentrations were located below the root zone. Correlation (P &lt; 0.001) between diurnal variations in O2 concentrations and incoming photosynthetically active radiation highlighted the importance of plant‐driven subsoil aeration of the root zone and the associated controls on coupled nitrification/denitrification. Therefore, P. arundinacea played an important role in facilitating N2O transport from the root zone to the atmosphere, and exclusion of the aboveground biomass in flux chamber measurements may lead to significant underestimations on net ecosystem N2O emissions. Complex interactions between seasonal changes in O2 and mineral‐N availability following near‐surface WL fluctuations in combination with plant‐mediated gas transport by P. arundinacea controlled the subsurface N2O concentrations and gas transport mechanisms responsible for N2O fluxes across the soil–atmosphere interface. Results demonstrate the necessity for addressing this high temporal variability and potential plant transport of N2O in future studies of net N2O exchange across the soil–atmosphere interface.

Introduction to Production, Transport, and Emission of Trace Gases from the Vadose Zone to the Atmosphere

Rising concerns about global warming as a consequence of increased anthropogenic greenhouse gas emissions have markedly strengthened scientific, political, and even public interest in issues surrounding human-induced climate change. This has resulted in fundamental economic and ecologic debates

Modeling Nitrous Oxide Emissions from Potato‐Cropped Soil

Intensive agricultural land use is considered to be the major source of the anthropogenic contribution to the increase in atmospheric N2O concentration during the last decades. A reduction of anthropogenic N2O emissions therefore requires a change in agricultural management practices. Mathematical models help to understand interacting processes in the N cycle and state variables affecting N2O emissions. The aim of this study was to test two modeling approaches for their ability to describe and quantify the seasonal variations of N2O fluxes in a potato (Solanum tuberosum L.)‐cropped soil. Model 1 assumes a fixed N2O/N2 ratio for N2O production and neglects the transport of N2O in the soil profile; Model 2 explicitly considers N2O transport and assumes a dynamic reduction of N2O to N2 Data for model evaluation came from an experiment where N2O fluxes were monitored during the vegetation period using a closed chamber technique. Generally, both modeling approaches were able to describe the observed seasonal dynamics of N2O emissions and events of high N2O emissions due to increased denitrification activity after heavy precipitation. The inclusion of a gas transport module in the modeling approach resulted in simulated N2O emission dynamics showing a smoother transient behavior. Extremely high emission rates from the interrow soil of the potato field were underestimated by both models. The lower N2O release from the ridge soil was mainly due to better aeration because of a lower soil bulk density and lower water contents caused by lateral runoff and root water uptake.

Predicting and monitoring the effects of large-scale ocean iron fertilization on marine trace gas emissions

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 364:283-288 (2008) - DOI: https://doi.org/10.3354/meps07549 Contribution to the Theme Section ‘Implications of large-scale iron fertilization of the oceans’ Predicting and monitoring the effects of large-scale ocean iron fertilization on marine trace gas emissions C. S. Law* National Institute of Water and Atmospheric Research (NIWA), Evans Bay Parade, Private Bag 14-901, Kilbirnie, Wellington 6241, New Zealand *Email: c.law@niwa.co.nz ABSTRACT: Large-scale (>40000 km2, >1 yr) ocean iron fertilization (OIF) is being considered as an option for mitigating the increase in atmospheric CO2 concentrations. However OIF will influence trace gas production and atmospheric emissions, with consequences over broad temporal and spatial scales. To illustrate this, the response of nitrous oxide (N2O) and dimethylsulphide (DMS) in the mesoscale iron addition experiments (FeAXs) and model scenarios of large-scale OIF are examined. FeAXs have shown negligible to minor increases in N2O production, whereas models of long-term OIF suggest significant N2O production with the potential to offset the benefit gained by iron-mediated increases in CO2 uptake. N2O production and emission will be influenced by the magnitude and rate of vertical particle export, and along-isopycnal N2O transport will necessitate monitoring over large spatial scales. The N2O–O2 relationship provides a monitoring option using oxygen as a proxy, with spatial coverage by Argo and glider-mounted oxygen optodes. Although the initial FeAXs exhibited similar increases (1.5- to 1.6-fold) in DMS, a subsequent sub-arctic Pacific experiment observed DMS consumption relative to unfertilized waters, highlighting regional variability as a complicating factor when predicting the effects of large-scale OIF. DMS cycling and its influence on atmospheric composition may be studied using naturally occurring blooms and be constrained prior to OIF by pre-fertilization spatial mapping and aerial sampling using new technologies. As trace gases may have positive or negative synergistic effects on atmospheric chemistry and climate forcing, the net effect of altered trace gas emissions needs to be considered in both models and monitoring of large-scale OIF. KEY WORDS: Iron fertilization · Trace gases · Nitrous oxide · Dimethlysulphide · Remineralization Full text in pdf format PreviousNextCite this article as: Law CS (2008) Predicting and monitoring the effects of large-scale ocean iron fertilization on marine trace gas emissions. Mar Ecol Prog Ser 364:283-288. https://doi.org/10.3354/meps07549Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 364. Online publication date: July 29, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

On the ability of chemical transport models to simulate the vertical structure of the N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O, NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and HNO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; species in the mid-latitude stratosphere

Abstract. In this paper we study the impact of the modelling of N2O on the simulation of NO2 and HNO3 by comparing in situ vertical profiles measured at mid-latitudes with the results of the Reprobus 3-D CTM (Three-dimensional Chemical Transport Model) computed with the kinetic parameters from the JPL recommendation in 2002. The analysis of the measured in situ profile of N2O shows particular features indicating different air mass origins. The measured N2O, NO2 and HNO3 profiles are not satisfyingly reproduced by the CTM when computed using the current 6-hourly ECMWF operational analysis. Improving the simulation of N2O transport allows us to calculate quantities of NO2 and HNO3 in reasonable agreement with observations. This is achieved using 3-hourly winds obtained from ECMWF forecasts. The best agreement is obtained by constraining a one-dimensional version of the model with the observed N2O. This study shows that the modelling of the NOy partitioning with better accuracy relies at least on a correct simulation of N2O and thus of total NOy.

N2O and NOy observations in the 1999/2000 Arctic polar vortex: Implications for transport processes in a CTM

We compare the evolution of simulated NOy and N2O with observations made during the 1999/2000 NASA Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone‐2000 to understand the different effects of transport on these two species and evaluate model transport processes in the Arctic lower stratosphere during mid to late winter. The simulations were made with the Goddard Space Flight Center chemistry and transport model, driven by meteorological analyses from the Goddard Data Assimilation Office. In January, model NOy and N2O distributions agree well with observations, provided a substantial loss of NOy due to polar stratospheric cloud sedimentation is included in the model simulation. In late winter, model NOy is ∼2–3 times larger than observed, despite the continued reasonable agreement of N2O. Anomalously large vertical transport of NOy due to overly vigorous descent in the CTM is primarily responsible for the large late winter NOy mixing ratios. However, the rapid descent is not apparent in the evolution of modeled N2O and presumably other similar species due to compensating horizontal transport of N2O across the vortex edge, which results in the reasonable agreement between modeled and measured N2O at ER‐2 altitudes throughout the winter. The need to properly represent the seasonal evolution of NOy when studying lower stratospheric polar wintertime photochemistry places strong constraints on the meteorological data used to drive global chemistry and transport models.

Isotopic variability of N2O emissions from tropical forest soils

We report measurements of the 15N and 18O signature of N2O emitted from tropical rain forest soils at the La Selva Biological station in Costa Rica and in the Fazenda Vitoria in the State of Pará, Brazil. The δ15N values ranged from −34 to 2‰ with respect to atmospheric N2, while δ18O values had a smaller range, from −4 to 18‰ with respect to atmospheric O2. We attribute these large variations to differences in microbial production, consumption, and transport of N2O. In general the δ15N of N2O emissions from an Oxisol soil in Brazil were consistently enriched by ∼20‰ in 15N compared to those from Ultisol and Inceptisol soils in Costa Rica. Denitrification is the most likely source of N2O in both locations during the rainy season, and the 15N of nitrate was similar in both locations. We attribute the overall variability in emitted 15N to differences in the ratio of N2O:N2 escaping from the soil to the atmosphere, with a larger fraction of the N2O reduced to N2 at the Brazilian sites. We found light δ15N‐N2O values associated with high N2O emissions in a fertilized agricultural site in Costa Rica and in a “hot spot” of high emissions in the forest site in Brazil. This result suggests that the increase of substrate availability might increase the fractionation associated with N2O production. Overall, the Brazilian Oxisol soils had the most enriched δ15N‐N2O emissions yet measured from soils. If these are more representative of tropical soil emissions than the Costa Rica emissions, then the globally averaged δ15N‐N2O tropical rain forest soil source is more enriched than previously estimated. The large variations in isotopic signature for N2O emissions demonstrate the potential utility of stable isotopes as tools for understanding the processes of N2O production and consumption in soils.

N2O transport in a three‐dimensional model driven by U. K. Meteorological Office winds

A three‐dimensional spectral chemical transport model truncated at T21 is employed to simulate N2O transport. The wind and vertical motion fields are taken from the U.K. Meteorological Office four‐dimensional assimilation data set. UARS cryogenic limb array etalon spectrometer (CLAES) N2O measurements are used to initialize the model in late August 1992. Model results are shown to simulate the CLAES measurements quite well over the first few months: N2O variability is similar at extratropical latitudes in the southern hemisphere over the period September 2–17, 1992, at 4.6 and 10 mbar, and there is good agreement in the synoptic maps of minor warmings during this period. Prior to a large warming event on September 30, minor stratospheric warmings are shown to produce negligible changes in the vortex below 4.6 mbar, but considerable mixing of air from the vortex edge and subtropical air is indicated. This results in a steepening of the N2O gradient at the vortex edge. During a warming event when the vortex center moves away from the pole, downward transport by the residual circulation can be large. This is offset by eddy transport effects, but these terms reverse during the recovery from the warming. From September 2 to 17, there is evidence of continuous mixing at midlatitudes at 4.6 mbar in contrast to more discontinuous, warming‐associated mixing at 10 mbar. The breakup of the vortex is initiated by the September 30 warming, and a warming on October 13 has a strong influence on the breakup. The breakup propagates downward. The climatological distribution of N2O in the tropics follows the seasonal variation of the solar radiation with a maximum, which is determined by the strength of the upward residual motion, shifting towards the summer hemisphere by 10°–15° latitude. The surf zone in both the model and the observations at the middle latitudes is well defined, but the gradients of N2O at the edge of the tropics and at the edge of the vortex are smaller in the model than in the observations. This is probably being caused by excessive mixing in the model.