Atmospheric Concentrations Of Nitrous Oxide Research Articles

Century-long changes and drivers of soil nitrous oxide (N2 O) emissions across the contiguous United States.

The atmospheric concentration of nitrous oxide (N2O) has increased by 23% since the pre‐industrial era, which substantially destructed the stratospheric ozone layer and changed the global climate. However, it remains uncertain about the reasons behind the increase and the spatiotemporal patterns of soil N2O emissions, a primary biogenic source. Here, we used an integrative land ecosystem model, Dynamic Land Ecosystem Model (DLEM), to quantify direct (i.e., emitted from local soil) and indirect (i.e., emissions related to local practices but occurring elsewhere) N2O emissions in the contiguous United States during 1900–2019. Newly developed geospatial data of land‐use history and crop‐specific agricultural management practices were used to force DLEM at a spatial resolution of 5 arc‐min by 5 arc‐min. The model simulation indicates that the U.S. soil N2O emissions totaled 0.97 ± 0.06 Tg N year−1 during the 2010s, with 94% and 6% from direct and indirect emissions, respectively. Hot spots of soil N2O emission are found in the US Corn Belt and Rice Belt. We find a threefold increase in total soil N2O emission in the United States since 1900, 74% of which is from agricultural soil emissions, increasing by 12 times from 0.04 Tg N year−1 in the 1900s to 0.51 Tg N year−1 in the 2010s. More than 90% of soil N2O emission increase in agricultural soils is attributed to human land‐use change and agricultural management practices, while increases in N deposition and climate warming are the dominant drivers for N2O emission increase from natural soils. Across the cropped acres, corn production stands out with a large amount of fertilizer consumption and high‐emission factors, responsible for nearly two‐thirds of direct agricultural soil N2O emission increase since 1900. Our study suggests a large N2O mitigation potential in cropland and the importance of exploring crop‐specific mitigation strategies and prioritizing management alternatives for targeted crop types.

Negative emission farming

In comparison with levels in 2000, global carbon dioxide (CO2) has increased by 43.5 ppm to 414.4 ppm during 2020, an increase of 12%. Indeed, concentration of atmospheric CO2 now is higher than at any time during the past 3.6 million years (Stein 2021). Similarly, the global average concentration of methane (CH4) for December of 2020 was 1,892.3 ppb, representing an increase of about 119 ppb (6%) since 2000 (Stein 2021). Despite the shutdown caused by the COVID-19 pandemic, the increase in atmospheric concentration of CO2 during 2020 may be among the largest for the entire period since the records started. There has also been notable increase in atmospheric concentration of nitrous oxide (N2O), primarily due to the use of nitrogenous fertilizers (WMO 2020). Thus, there is a strong need to identify sources and sinks of these gases, especially those of CH4 and N2O, which are 28 and 285 times more potent, respectively, in trapping heat than is CO2 (IPCC 2007). While known sources include fossil fuel combustion, land use conversion, biomass burning, rice paddies, cattle production, etc., the role of soil processes has not been given the emphasis that is deserves. Whereas science-based and sustainable use of soils of agro-ecosystems and other managed land uses can be a sink for CO2 and CH4, soils prone to degradation by diverse processes (e.g., decline in soil structure, compaction, anaerobiosis, erosion/deposition) can be sources of CH4 through methanogenesis and of N2O through nitrification and denitrification. The impact of soil degradation, difficult and challenging to quantify as it may be, …

Machine learning based analysis for relation between global temperature and concentrations of greenhouse gases

Climate change is an important topic that needs to be addressed soon. As the consequences of climate change are extremely serious, such as ocean acidification and extreme weather conditions, it is paramount to learn what are the causes behind the phenomenon to battle it effectively. In this work, authors modeled the relationship between global temperatures and atmospheric concentrations of nitrous oxide, methane, and carbon dioxide on a dataset of 65 years using linear regression, decision tree regression, random forest regression, and Artificial Neural Network. Authors have analyzed the performance of these machine learning algorithms on the data and established that ANN outperforms the other algorithms on the basis of mean square error. Further authors have calculated the importance of each feature (carbon dioxide, methane, and nitrous oxide) using the best performing model-ANN and proved that the contribution of carbon dioxide in the increase of global temperatures is the maximum of the given greenhouse gases.

N<sub>2</sub>O changes from the Last Glacial Maximum to the preindustrial – Part 1: Quantitative reconstruction of terrestrial and marine emissions using N<sub>2</sub>O stable isotopes in ice cores

Abstract. Using high-precision and centennial-resolution ice core information on atmospheric nitrous oxide concentrations and its stable nitrogen and oxygen isotopic composition, we quantitatively reconstruct changes in the terrestrial and marine N2O emissions over the last 21 000 years. Our reconstruction indicates that N2O emissions from land and ocean increased over the deglaciation largely in parallel by 1.7±0.3 and 0.7±0.3 TgN yr−1, respectively, relative to the Last Glacial Maximum level. However, during the abrupt Northern Hemisphere warmings at the onset of the Bølling–Allerød warming and the end of the Younger Dryas, terrestrial emissions respond more rapidly to the northward shift in the Intertropical Convergence Zone connected to the resumption of the Atlantic Meridional Overturning Circulation. About 90 % of these large step increases were realized within 2 centuries at maximum. In contrast, marine emissions start to slowly increase already many centuries before the rapid warmings, possibly connected to a re-equilibration of subsurface oxygen in response to previous changes. Marine emissions decreased, concomitantly with changes in atmospheric CO2 and δ13C(CO2), at the onset of the termination and remained minimal during the early phase of Heinrich Stadial 1. During the early Holocene a slow decline in marine N2O emission of 0.4 TgN yr−1 is reconstructed, which suggests an improvement of subsurface water ventilation in line with slowly increasing Atlantic overturning circulation. In the second half of the Holocene total emissions remain on a relatively constant level, but with significant millennial variability. The latter is still difficult to attribute to marine or terrestrial sources. Our N2O emission records provide important quantitative benchmarks for ocean and terrestrial nitrogen cycle models to study the influence of climate on nitrogen turnover on timescales from several decades to glacial–interglacial changes.

Cropping system history and crop rotation phase drive the abundance of soil denitrification genes nirK, nirS and nosZ in conventional and organic grain agroecosystems

While nitrogen fertilizers have helped increase crop yields substantially, they have also contributed to several environmental problems, including an increasing atmospheric concentration of nitrous oxide (N2O), a greenhouse gas (GHG) and catalyst of stratospheric ozone decay. The dominant source of atmospheric N2O in many agricultural soils is denitrification, a process carried out by soil microbes containing the genes for nitrate reductase (Nar), nitrite reductase (Nir), nitric oxide reductase (Nor) and/or nitrous oxide reductase (Nos). We monitored the abundance of soil nirK, nirS, and nosZ genes during the summer growing season. We sampled replicated field plots from a long-term agricultural research site that includes agroecosystems with corn/soybean/wheat/legume rotations: two tilled-organic systems (Org3 and Org6), and two conventional systems, one using a chisel plow for primary tillage (CT) and one using no-tillage (NT). We demonstrate that nirK copy number in soil was affected primarily by the phase of the crop rotation and secondarily by time of year, regardless of cropping system. In contrast, nosZ gene copy number was primarily driven by cropping system. Soil N2O emissions during the sampling period were highest in Org3 and lowest in NT. However, gene quantities did not correspond to N2O emissions patterns, indicating that quantitative PCR of key denitrification genes measured at the temporal resolution reported here is not a good predictor of soil N2O emissions. These results, nonetheless, show that cropping system management can affect microbial community composition, gene quantity of nir and nos genes and N2O emissions. We found cropping system and time of year captured variation in gene abundance among microbial denitrifier populations in these agricultural soils.

Early, Subclinical Hematological Changes Associated with Occupational Exposure to High Levels of Nitrous Oxide.

This study was undertaken to determine whether exposure of operating room personnel to inhalation anesthetics, nitrous oxide, isoflurane, and sevoflurane was associated with any hematological changes. This historical cohort study was performed in 2018 at a large public hospital in Shiraz, where 52 operating room personnel and 52 administrative staff were investigated. The blood sample was taken from all individuals for Complete Blood Count. Furthermore, demographic information was collected through questionnaires. Mean atmospheric concentrations of nitrous oxide, isoflurane, and sevoflurane, to which subjects were exposed, were 850.92, 2.40, and 0.18 ppm, respectively. The hematological parameters were within the normal range in both groups. However, the mean values of hemoglobin, hematocrit, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and red blood cell count in the exposed group were significantly lower than the control group. No significant differences were noted between the two groups as far as other hematological factors were concerned. These findings provide circumstantial evidence to further substantiate the notion that occupational exposure to inhalation anesthetics, under the exposure scenario explained in this study, is associated with subtle, subclinical, prepathologic hematological changes. Long-term consequence and ramifications of these effects require further investigation. The range of exposure levels to anesthetic gases in operating rooms.

Nitrogen deposition induced significant increase of N2O emissions in an dry alpine meadow on the central Qinghai–Tibetan Plateau

Atmospheric concentrations of nitrous oxide (N2O) have increased over the last 150 years due to human activities. Soils are important source of N2O where its production is largely regulated by biological processes. Nitrogen (N) deposition can alter the processes of autotrophic nitrification and denitrification, thus affecting the rate and direction of the soil N2O exchange with the atmosphere. It is obvious that atmospheric N deposition has influenced a dry alpine meadow in the Qinghai–Tibetan Plateau (QTP). Therefore, we investigated the effects of N deposition on the annual N2O emissions in an alpine meadow of the QTP. The N2O flux was measured for 2 years using static chambers and gas chromatography methods at four treatments (N0, background level; N7, add 7 kg N ha−1 yr−1; N20, add 20 kg N ha−1 yr−1; N40, add 40 kg N ha−1 yr−1). We found that high N deposition increased the N2O flux, not only in the growing season but also in winter and the spring thaw period. The average annual N2O fluxes at N0 and N40 plots were 3.1 and 6.1 μg m−2 h−1, respectively. Compared with N0, the average annual N2O fluxes increased at N7, N20, and N40 plots by 13.7%, 47.6%, and 98.7%, respectively, the N2O fluxes in N40 plots increased by 113.6%, 41.6%, and 78.7% during the growing season, winter and spring thaw period, respectively. The emission of N2O during the growing season, winter and spring thaw period accounted for 63.2%, 29.9% and 6.9% of annual total emission of N2O, respectively. The N2O flux correlated significantly with air temperature, soil temperature, soil water content, total nitrogen, total organic carbon, and soil NH4+–N content in the alpine meadow.

First results of tall tower based nitrous oxide flux monitoring over an agricultural region in Central Europe

Nitrous oxide is one of the atmospheric greenhouse gases whose amount is significantly influenced by human activity. Its major anthropogenic sources are the agricultural soils but the emission is known only with large uncertainty yet. The paper presents a tall tower based measuring system installed in Hungary, which is designed for the long-term monitoring of nitrous oxide emission of a regionally typical composition of agricultural fields by means of eddy covariance technique. Due to the careful calibration of the gas analyzer applied the measuring system is also suitable for the recording of the atmospheric concentration of nitrous oxide on the globally compatible scale (WMO X2006A). The paper reports the results of the first two years of the monitoring program, which is the first of its kind in Central Europe. For the period of July 2015–June 2017 the concentration measurements indicate an increasing trend of 0.91 nmol mol−1 year−1 with an average concentration of 330.64 nmol mol−1. During the two years of the project, the monitoring system recorded a total of 441 ± 195 mg N2O-N m−2 nitrous oxide emission with late spring/early summer maximum. The measurements also revealed the episodic nature of the emission typically triggered by major precipitation events.

Nitrification gene ratio and free ammonia explain nitrite and nitrous oxide production in urea-amended soils

The atmospheric concentration of nitrous oxide (N2O), a potent greenhouse gas and ozone-depleting chemical, continues to increase, due largely to the application of nitrogen (N) fertilizers. While nitrite (NO2−) is a central regulator of N2O production in soil, NO2− and N2O responses to fertilizer addition rates cannot be readily predicted. Our objective was to determine if quantification of multiple chemical variables and structural genes associated with ammonia (NH3)- (AOB, encoded by amoA) and NO2−-oxidizing bacteria (NOB, encoded by nxrA and nxrB) could explain the contrasting responses of eight agricultural soils to five rates of urea addition in aerobic microcosms. Significant differences in NO2− accumulation and N2O production by soil type could not be explained by initial soil properties. Biologically-coherent statistical models, however, accounted for 70–89% of the total variance in NO2− and N2O. Free NH3 concentration accounted for 50–85% of the variance in NO2− which, in turn, explained 62–82% of the variance in N2O. By itself, the time-integrated nxrA:amoA gene ratio explained 78 and 79% of the variance in cumulative NO2− and N2O, respectively. In all soils, nxrA abundances declined above critical urea addition rates, indicating a consistent pattern of suppression of Nitrobacter-associated NOB due to NH3 toxicity. In contrast, Nitrospira-associated nxrB abundances exhibited a broader range of responses, and showed that long-term management practices (e.g., tillage) can induce a shift in dominant NOB populations which subsequently impacts NO2− accumulation and N2O production. These results highlight the challenges of predicting NO2− and N2O responses based solely on static soil properties, and suggest that models that account for dynamic processes following N addition are ultimately needed. The relationships found here provide a basis for incorporating the relevant biological and chemical processes into N cycling and N2O emissions models.

Reducing nitrous oxide emissions by changing N fertiliser use from calcium ammonium nitrate (CAN) to urea based formulations

The accelerating use of synthetic nitrogen (N) fertilisers, to meet the world's growing food demand, is the primary driver for increased atmospheric concentrations of nitrous oxide (N2O). The IPCC default emission factor (EF) for N2O from soils is 1% of the N applied, irrespective of its form. However, N2O emissions tend to be higher from nitrate-containing fertilisers e.g. calcium ammonium nitrate (CAN) compared to urea, particularly in regions, which have mild, wet climates and high organic matter soils. Urea can be an inefficient N source due to NH3 volatilisation, but nitrogen stabilisers (urease and nitrification inhibitors) can improve its efficacy. This study evaluated the impact of switching fertiliser formulation from calcium ammonium nitrate (CAN) to urea-based products, as a potential mitigation strategy to reduce N2O emissions at six temperate grassland sites on the island of Ireland. The surface applied formulations included CAN, urea and urea with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and/or the nitrification inhibitor dicyandiamide (DCD). Results showed that N2O emissions were significantly affected by fertiliser formulation, soil type and climatic conditions. The direct N2O emission factor (EF) from CAN averaged 1.49% overall sites, but was highly variable, ranging from 0.58% to 3.81. Amending urea with NBPT, to reduce ammonia volatilisation, resulted in an average EF of 0.40% (ranging from 0.21 to 0.69%)-compared to an average EF of 0.25% for urea (ranging from 0.1 to 0.49%), with both fertilisers significantly lower and less variable than CAN. Cumulative N2O emissions from urea amended with both NBPT and DCD were not significantly different from background levels. Switching from CAN to stabilised urea formulations was found to be an effective strategy to reduce N2O emissions, particularly in wet, temperate grassland.

29 % N2O emission reduction from a modelled low-greenhouse gas cropping system during 2009–2011

Atmospheric concentration of nitrous oxide (N2O), a greenhouse gas (GHG), is rising largely due to agriculture. At the plot scale, N2O emissions from crops are known to be controlled by local agricultural practices such as fertilisation, tillage and residue management. However, knowledge of greenhouse gas emissions at the scale of the cropping system is scarce, notably because N2O monitoring is time consuming. Strategies to reduce impact of farming on climate should therefore be sought at the cropping system level. Agro-ecosystem models are simple alternative means to estimate N2O emissions. Here, we combined ecosystem modelling and field measurements to assess the effect of agronomic management on N2O emissions. The model was tested with series of daily to monthly N2O emission data. It was then used to evaluate the N2O abatement potential of a low-emission system designed to halve greenhouse gas emissions in comparison with a system with high productivity and environmental performance. We found a 29 % N2O abatement potential for the low-emission system compared with the high-productivity system. Among N2O abatement options, reduction in mineral fertiliser inputs was the most effective.

What are the impacts of grazing and cutting events on the N2O dynamics in humid temperate grassland?

Atmospheric concentrations of nitrous oxide (N2O) have been increasing over the last century with much of this increase from agricultural soils, fertilized with nitrogen. To understand the N2O emissions from terrestrial ecosystems (e.g. grassland soils) it is necessary to understand the processes leading to N2O production. From February to August in 2010, we conducted a field study to measure the N2O fluxes using the chamber technique, at a grazed and cut grassland site in South West Ireland. The objectives of the study were: 1) to understand the temporal variation of the N2O fluxes during the spring and summer periods; 2) to examine the separate effects of grazing and cutting events on N2O fluxes; and 3) to examine the relationship of soil ammonium (NH4+−N) and soil nitrate (NO3--N) with N2O fluxes. We found the highest peak of daily N2O flux occurred at the start of spring; however the total of summer fluxes (June, July and August) of 1.81±0.7kg N2O–Nha−1 were higher than those of the spring (March, April and May) fluxes of 1.51±0.6kg N2O–Nha−1. The soil NH4+−N concentration was higher than the soil NO3–N concentration over the study period and elevated N2O fluxes coincided with elevated soil NH4–N concentrations. There were two short (2day duration) cattle grazing events; one on April 26/27 and the second on June 27/28. There were two grass cutting (for silage) events: on May 30 and on August 4. After the two grazing and two cutting events, the N2O fluxes increased markedly. After both grazing events, there was an immediate step increase of ~200μg N2O–Nm−2h−1, after which the fluxes decreased over the next few weeks. After both cutting events, there was a gradual increase in N2O fluxes over the next several weeks. We found that the N2O flux increases post grazing, were due to grazing only, since the other variables (soil temperature, WFPS, N application) did not change. However, the flux increases post cutting could not ascribed to cutting only, as other flux favouring variables of: changes in soil temperature and WFPS also occurred at this time. The N2O fluxes correlated better with soil NH4–N concentration (r2=0.73 (p=<0.05)) than with NO3--N (r2=0.25 (p=not significant)). The occurrence of elevated NH4–N in conjunction with elevated WFPS, frequently in the range of 50–60% suggests that nitrification rather than denitrification was likely the dominant process involved in the production of N2O at this site.

Linear and nonlinear dependency of direct nitrous oxide emissions on fertilizer nitrogen input: A meta-analysis

Rising atmospheric concentrations of nitrous oxide (N2O) contribute to global warming and associated climate change. It is often assumed that there is a linear relationship between nitrogen (N) input and direct N2O emission in managed ecosystems and, therefore, direct N2O emission for national greenhouse gas inventories use constant emission factors (EF). However, a growing body of studies shows that increases in direct N2O emission are related by a nonlinear relationship to increasing N input. We examined the dependency of direct N2O emission on N input using 26 published datasets where at least four different levels of N input had been applied. In 18 of these datasets the relationship of direct N2O emission to N input was nonlinear (exponential or hyperbolic) while the relationship was linear in four datasets. We also found that direct N2O EF remains constant or increases or decreases nonlinearly with changing N input. Studies show that direct N2O emissions increase abruptly at N input rates above plant uptake capacity. The remaining surplus N could serve as source of additional N2O production, and also indirectly promote N2O production by inhibiting biochemical N2O reduction. Accordingly, we propose a hypothetical relationship to conceptually describe in three steps the response of direct N2O emissions to increasing N input rates: (1) linear (N limited soil condition), (2) exponential, and (3) steady-state (carbon (C) limited soil condition). In this study, due to the limited availability of data, it was not possible to assess these hypothetical explanations fully. We recommend further comprehensive experimental examination and simulation using process-based models be conducted to address the issues reported in this review.

Trends and seasonal cycles in the isotopic composition of nitrous oxide since 1940

The atmospheric nitrous oxide concentration has increased by 20% since 1750. Analyses of Antarctic firn and archived air samples reveal seasonal cycles in the isotopic signature of nitrous oxide, which can help to disentangle the contribution of surface sources.

Interesting Times for Marine N 2 O

Changes in ocean chemistry could exacerbate global warming by raising the atmospheric concentration of nitrous oxide, a potent greenhouse gas.

Nitrous Oxide: No Laughing Matter

Rising atmospheric concentrations of nitrous oxide are contributing to global warming and stratospheric ozone destruction.

The contribution of manure and fertilizer nitrogen to atmospheric nitrous oxide since 1860

Atmospheric nitrous oxide concentrations have been increasing since the industrial revolution and currently account for 6% of total anthropogenic radiative forcing. Microbial production in soils is the dominant nitrous oxide source; this has increased with increasing use of nitrogen fertilizers. However, fertilizer use alone cannot account for the historical trends of atmospheric concentrations of nitrous oxide. Here, I analyse atmospheric concentrations, industrial sources of nitrous oxide, and fertilizer and manure production since 1860. Before 1960, agricultural expansion, including livestock production, may have caused globally significant mining of soil nitrogen, fuelling a steady increase in atmospheric nitrous oxide. After 1960, the rate of the increase rose, due to accelerating use of synthetic nitrogen fertilizers. Using a regression model, I show that 2.0% of manure nitrogen and 2.5% of fertilizer nitrogen was converted to nitrous oxide between 1860 and 2005; these percentage contributions explain the entire pattern of increasing nitrous oxide concentrations over this period. Consideration of processes that re-concentrate soil nitrogen, such as manure production by livestock, improved ‘hind-casting’ of nitrous oxide emissions. As animal protein consumption in human diets increases globally, management of manure will be an important component of future efforts to reduce anthropogenic nitrous oxide sources. Atmospheric concentrations of nitrous oxide, a greenhouse gas, have increased since 1860. A regression model indicates that conversion of 2% of manure nitrogen and 2.5% of fertilizer nitrogen could explain the pattern of increasing nitrous oxide concentrations between 1860 and 2005, including a rise in the rate of increase around 1960.

Glacial–interglacial and millennial-scale variations in the atmospheric nitrous oxide concentration during the last 800,000 years

We present records of atmospheric nitrous oxide obtained from the ice cores of the European Project for Ice Coring in Antarctica (EPICA) Dome C and Dronning Maud Land sites shedding light on the concentration of this greenhouse gas on glacial–interglacial and millennial time scales. The extended EPICA Dome C record covers now all interglacials of the last 800,000 years and reveals nitrous oxide variations in concert with climate. Highest mean interglacial nitrous oxide concentrations of 280 parts per billion by volume are observed during the interglacial corresponding to Marine Isotope Stage 11 around 400,000 years before present, at the same time when carbon dioxide and methane reach maximum mean interglacial concentrations. The temperature reconstruction at Dome C indicates colder interglacials between 800,000 and 440,000 years before present compared to the interglacials of the last 440,000 years. In contrast to carbon dioxide and methane, which both respond with lower concentrations at lower temperatures, nitrous oxide shows mean interglacial concentrations of 4–19 parts per billion by volume higher than the preindustrial Holocene value during the interglacials corresponding to Marine Isotope Stage 9–19. At the end of most interglacials, nitrous oxide remains substantially longer on interglacial levels than methane. Nevertheless, nitrous oxide shows millennial-scale variations at the same time as methane throughout the last 800,000 years. We suggest that these millennial-scale variations have been driven by a similar mechanism as the Dansgaard/Oeschger events known from the last glacial. Our data lead to the hypothesis that emissions from the low latitudes drive past variations of the atmospheric nitrous oxide concentration.

Variations of atmospheric nitrous oxide concentration in the northern and western Pacific

Variations of atmospheric nitrous oxide concentration in the northern and western Pacific

Variations of atmospheric nitrous oxide concentration in the northern and western Pacific

Atmospheric N2O concentrationwas observed in the Pacific for the period 1991–2006, using commercial container ships sailing between Japan and North America and between Japan and Australia or New Zealand. The N2O concentration showed a secular increase and interannual variations at all sampling locations, but a seasonal cycle was detectable only at northern high latitudes. The annual mean N2O concentration showed little longitudinal variations (within ± 0.3 ppb) in the northern Pacific, but showed a clear north-south gradient of about 0.8 ppb, with higher values in the Northern Hemisphere. The annual mean N2O was also characterized by especially high values at 30◦N due to strong local N2O emissions and by a steep latitudinal decrease from the equator to 20◦S due to the suppression of interhemispheric exchange of air by the South Pacific Convergence Zone. The N2O growth rate showed an interannual variation with a period of about 3 yr (high-values in 1999 and 2000), with a delayed eastward and poleward phase propagation in the northern and western Pacific, respectively. The interannual variations of the N2O growth rate and soil water showed a good correlation, suggesting that the N2O emission from soils have an important causative role in the atmospheric N2O variation.