Greenhouse Gas N2O Research Articles

Effect of La/Ce modification over Cu based Y zeolite catalysts on high temperature selectivity for selective catalytic reduction with ammonia

CuY zeolite catalyst is considered to be one of most promising catalysts for selective catalytic reduction with ammonia (NH3-SCR), but its main byproduct is the greenhouse gas N2O. To increase N2 selectivity, the modification mode and promotion mechanism of La/Ce doping with two-step ion exchange method were investigated. Impressively, CuLaY achieved above 90% efficiency from 140 °C to 380 °C and less N2O production especially at the temperature above 250 °C. The characterization results showed La/Ce doping increased the content of surface Cu2+ species and improved the oxidation ability of Cu ions in catalysts. However, the formation of La/Ce oxides on the zeolite surface had an adverse impact on the SCR activity, while Ce oxides were more easily formed than La oxides. In addition, more abundant adsorbed NOx species and stronger NH3 adsorption on the surfaces enhanced L-H mechanism for CuLaY with high N2 selectivity above 250 °C.

Warming and redistribution of nitrogen inputs drive an increase in terrestrial nitrous oxide emission factor

Anthropogenic nitrogen inputs cause major negative environmental impacts, including emissions of the important greenhouse gas N2O. Despite their importance, shifts in terrestrial N loss pathways driven by global change are highly uncertain. Here we present a coupled soil-atmosphere isotope model (IsoTONE) to quantify terrestrial N losses and N2O emission factors from 1850-2020. We find that N inputs from atmospheric deposition caused 51% of anthropogenic N2O emissions from soils in 2020. The mean effective global emission factor for N2O was 4.3 ± 0.3% in 2020 (weighted by N inputs), much higher than the surface area-weighted mean (1.1 ± 0.1%). Climate change and spatial redistribution of fertilisation N inputs have driven an increase in global emission factor over the past century, which accounts for 18% of the anthropogenic soil flux in 2020. Predicted increases in fertilisation in emerging economies will accelerate N2O-driven climate warming in coming decades, unless targeted mitigation measures are introduced.

LaNiO3 as a Pt catchment material in the ammonia oxidation process

Platinum is lost as gaseous PtO2 from the Pt-Rh (typically 95:5 wt%) catalyst used in the ammonia oxidation process. The most common technology utilized today for recovering PtO2 from the gas stream is to apply Pd-Ni (95:5 wt%) catchment gauzes. However, the technology suffers due to loss of Pd at the same time as a severe reconstruction of the alloy creates a large pressure drop during operation. In the search of alternative materials, LaNiO3 is considered as an interesting Pt catchment material. The evaluation is based on lab-scale Pt catchment experiments in a gas flow of dry air using a six-zone furnace with a Pt source placed at 1000 °C to create gaseous PtO2, and LaNiO3 pellets placed downstream at 700 – 900 °C. The duration of the experiments varied from 1 to 26 days, and scanning electron microscopy – energy dispersive X-ray analysis and powder X-ray diffraction were utilized to prove the catchment of Pt. The key finding is that LaNiO3 captures Pt and transforms via the non-stoichiometric rhombohedral LaNi1−xPtxO3 (x ≤ 0.075) and monoclinic La2Ni2−2xPt2xO6 (0.20 ≤ x < 0.50) perovskites into La2NiPtO6 (x = 0.50). Pt catchment is poor at 700 °C, but a substantial activity is documented at 800 and 900 °C. We furthermore demonstrate the recovery of Pt from the oxide by a wet chemical approach, and both LaNiO3 and La2NiPtO6 have been tested as potential catalysts for decomposition of NOx and N2O at relevant temperatures. LaNiO3 is not catalytically active in decomposition of NOx, the main ammonia oxidation products, while La2NiPtO6 has a minor catalytic activity toward NOx decomposition (1–2 %). However, both materials decompose the greenhouse gas N2O fully at 900 °C.

Effects of nitrogen and water addition on N2O emissions in temperate grasslands, northern China

Temperate grasslands are considered an important natural source of the trace greenhouse gas N2O, which has attracted much attention in recent years. Increased annual precipitation and N deposition have been observed in temperate grasslands in northern China owing to climate change and anthropogenic activities. Although the individual effects of increased precipitation and N deposition on N2O emissions have been extensively reported, their interactive effects remain unclear. An in situ experiment with two levels of water supply (ambient and +15% precipitation levels) and four levels of N application (0, 25, 50, and 100 kg N ha−1 yr−1) was conducted in a semi-arid temperate grassland from 2016 to 2018 to quantify the effects of additional precipitation and N on N2O emissions in temperate grasslands. The results showed that temperate grasslands are a small source of N2O with negative N2O fluxes during the growing seasons. Water addition amplified the variability in N2O fluxes by lowering the mean N2O fluxes and strengthening N2O emission pulses triggered by precipitation. The trade-off between increased N2O emission pulses and decreased mean fluxes resulted in decreased growing season cumulative N2O emissions. The stimulated N2O emissions by N addition were linearly related to N application rates. However, this linear correlation shifted to similar N2O emissions among the N application rates by water addition. In addition, N2O emissions were negatively correlated with soil moisture and microbial biomass carbon (MBC) but positively correlated with soil dissolved organic carbon (DOC), NH4+, and NO3−. Our results suggest that (1) water addition increases the sensitivity of N2O emissions to N addition and limits the loss of additional N as N2O. (2) In addition to directly increasing N2O emissions, N addition increases N2O emissions indirectly by increasing soil DOC, NH4+, and NO3− levels, whereas water addition decreases N2O emissions indirectly by increasing MBC and soil moisture. (3) The ability of soil properties to explain the variability in N2O fluxes was limited, whereas the ability of soil properties to explain the interannual variability in cumulative N2O emissions was highly reliable.

Appropriate Irrigation and Fertilization Regime Restrain Indigenous Soil Key Ammonia-Oxidizing Archaeal and Bacterial Consortia to Mitigate Greenhouse Gas Emissions

Harnessing an ammonia-oxidizing microbiome has become an increasingly attractive form of management for mitigating greenhouse gas emissions in rice paddies; however, the relationship between greenhouse gas emissions and ammonia-oxidizing microbiomes, using a nitrogen application and irrigation regime, has not been well investigated. To decipher which of (and how) the specific mmonia-oxidizing bacterial species drive the greenhouse gas CH4 and N2O emissions, a field experiment with varying nitrogen application and irrigation regimes was initiated to investigate the succession of key bacterial consortia associated with GHG emissions. The results showed that water-saving irrigation (AWD) significantly increased NO3-N and NH4+-N concentrations, compared with conventional irrigation (FDF), whereas (total nitrogen) TN was little higher in FDF (1.38 g kg−1) compared with the AWD (1.36 g kg−1). During the rice-growing season, CH4 emissions ascended speedily, and emissions peaked at maximum values of 3.32 and 4.41 ug mg−2 h−1 on day 5 in FDF and AWD irrigation regimes, respectively, and then they rapidly decreased during the midseason period, maintaining a relatively low emission rate until the rice was harvested. The patterns of N2O emission fluxes had the same tendencies with N fertilization. Putative key taxa, such as Flavobacterium, Massilia, Arenimonas, Novosphingobium, Pseudomonas, exhibited significant positive relationships with higher GHG emissions, suggesting that they make particularly obvious contributions to N2O emissions. These putative taxa should be considered when designing a high nitrogen application and irrigation strategy. As such, the nitrogen application of N180, and the irrigation regimes of water-saving irrigation, are recommended methods for N conservation and the mitigation of greenhouse gas emissions in rice paddies.

Improved Nitrogen Use Efficiency and Greenhouse Gas Emissions in Agricultural Soils as Producers of Biological Nitrification Inhibitors.

Based on an analysis of the current situation of nitrogen fertiliser application, it is suggested that improving the nitrogen utilisation efficiency of crops is an important means of promoting the sustainable development of agriculture and realises the zero increase in chemical fertiliser application. Nitrate loss and nitrous oxide (N2O) emissions caused by nitrification and denitrification are the main reasons for the low utilisation rate of nitrogen fertilisers. N2O is a greenhouse gas that has caused a sharp increase in global temperature. Biological nitrification inhibition refers to releasing natural compounds that inhibit nitrification from plant roots. The natural compounds released are called biological nitrification inhibitors (BNIs), which specifically inhibit the activity of microorganisms in soil nitrification. Biological nitrification inhibitors can significantly improve rice (Oryza sativa), corn (Zea mays) and other crops by 5–10%, which can increase the nitrogen utilisation rate of corn by 3.1%, and reduce greenhouse gas N2O emissions. Compared with plants that do not produce BNI, the amount of N2O released can be reduced by up to 90%. The BNI released by Brachialactone (Brachiaria humidicola) accounted for 60–90% of the total inhibition of nitrification. In summary, biological nitrification inhibitors that inhibit nitrification, improve nitrogen utilisation and crop yield, and reduce greenhouse gas emissions play an important role. This paper reviews the plants known to release BNIs, reviews the plants known to inhibit soil nitrification but with unknown BNIs and further discusses the important role of bio nitrification inhibition in agricultural systems.

Long-Term Variation of Greenhouse Gas N2O Observed by MLS during 2005–2020

Nitrous oxide (N2O) is a potent and long-lived greenhouse gas that contributes to global warming with a global warming potential (GWP) 298 times that of carbon dioxide (CO2). In this paper, we analyzed the trend of N2O concentration in vertical layers of the stratosphere from 2005 to 2020 using the N2O observed from the Microwave Limb Sounder (MLS) that is on board the Aura satellite. We found that the local N2O concentration showed a downward trend in the lower stratosphere but rose or fluctuated in the upper stratosphere. The reduction reached −5 ppb/yr at pressure levels of 31.62 hPa and 68.13 hPa, with a confidence level of over 90%. The growth was around 1–2 ppb/yr in the upper stratosphere. In addition, a concentration anomaly was observed in the tropical stratosphere in 2013. After the appearance of this anomaly, the N2O concentration in the middle and lower layers of the tropical stratosphere was lower than before 2013. We speculated that the enhancement of the Brewer–Dobson circulation (BDC) upwelling before and after stratospheric sudden warming (SSW) is the main reason for the abnormal concentration distribution in 2013. Stratospheric N2O has changed significantly in the past 16 years with the mutual coupling effect of BDC and SSW and such changes can have further impact on the chemical equilibrium and radiation balance in the stratosphere, as well as on the persistent climate-warming trend.

New Insights into the Use of Rhizobia to Mitigate Soil N2O Emissions

Agriculture is a major anthropogenic source of the greenhouse gas N2O, which is also involved in stratospheric ozone depletion. While the use of rhizobial inoculants has already been reported as an emerging option for mitigating soil N2O emissions, this study presents an in situ abatement of 70% of soil N2O emission using the strain nosZ+ G49 vs. nosZ− USDA138 in association with soybean. Therefore, we consider that the choice of the inoculant strain of a leguminous crop should take into account the capacity of strains to reduce nitrous oxide in addition to their N fixation capacity. This study also clearly suggests that this mitigation option could be considered not only for soybean but also for different leguminous crops, with emphasis currently placed on lupin because of the potential of its association with the nosZ+ LL200 strain. The clear demonstration of the N2O reduction capacity of clover symbiotic strains suggests that opportunities for mitigation might also occur on grassland.

Short-Term Effects of Increasing Compost Application Rates on Soil C and Greenhouse Gas (N2o and Co2) Emissions in a California Central Coast Vineyard

Short-Term Effects of Increasing Compost Application Rates on Soil C and Greenhouse Gas (N2o and Co2) Emissions in a California Central Coast Vineyard

Reduction of N2O with hydrosilanes catalysed by RuSNS nanoparticles.

A series of RuSNS nanoparticles, prepared by decomposition of Ru(COD)(COT) with H2 in the presence of an SNS ligand, have been found to catalyse the reduction of the greenhouse gas N2O to N2 employing different hydrosilanes.

Greenhouse gas capture by triboelectric charging

A quartz ampoule with quartz grains is mechanically activated in a dry air-like atmosphere with 0.5 % of one of the major greenhouse gases CO2, CH4, and N2O. The grains rub against each other and the walls of the ampoule during activation, leading to triboelectric charging and erosion. IR spectroscopy shows the greenhouse gases disappear during activation. After activation, the ampoule rests for five days. IR spectra recorded after this period show no reappearance of the greenhouse gases.

Determining of Aircraft Engine Greenhouse Gas (CO2, CH4 and N2O) Emissions from the Landing and Take-Off Operations Around the Airport Area

Recently, environmental concerns arising from aviation activities have increased, and studies on the environmental aspect of aircraft operations within the concept of sustainable and cleaner aviation have become one of the important research topics. In this study, the Greenhouse Gas (GHG) Emissions, namely CO2, CH4 and N2O pollutants emitted to the environment during the landing and take-off operations in the International Eskisehir Hasan Polatkan Airport (LTBY) of aircraft engines were analyzed with the help of predictive approaches. Additionally, the average jet-fuel consumptions of these aircraft were determined. Calculations were performed in point of the method of the Intergovernmental Panel on Climate Change (IPCC) and performed with the Tier-2 predictive approach. According to results, it has been obtained that the Airbus 321 (A-321) series aircraft has the highest pollution with a value of 762495 kg/ year of GHG. Furthermore, it has been observed that approximately 1127 tons/year of CO2, 48.14 kg/year of CH4 and 39.77 kg/year of N2O were released into the environment. On the other hand, the total value of jet-fuel consumption during the landing and take-off operations of these aircraft is calculated to be an average of 357 tons/year. On the other hand, it has been determined that the Boeing B767-300 series aircraft (B763) is the most inefficient type of aircraft depending on the fuel consumption by performing a correlation between the parameters of average Jet-fuel consumption and total Landing and Take-off count.

Grass Growth and N2O Emissions From Soil After Application of Jellyfish in Coastal Areas

The supply of nutrients for agricultural production faces enormous challenges as food security and sustainability goals have to be ensured. Processing of marine biomass has high potential to provide nutrients for agricultural purposes in coastal areas. One underexplored resource are jellyfish, which occur as blooms and by-catch of the fishing industry. In this context, a pot experiment investigated the effects of jellyfish as a fertilizer on biomass accumulation of annual ryegrass (Lolium multiflorum), and its effect on the important greenhouse gas N2O as a sustainability indicator of novel fertilizers. Dried and ground jellyfish was applied [3 species: Aurelia aurita (AA), Cyanea capillata (CC), Periphylla periphylla (PP)] and compared with an unfertilized and a mineral fertilized (calcium-ammonium-nitrate, CAN) treatment. Dried jellyfish and CAN were applied at equal N rates of 5 g N per m2. The N2O-fluxes from soil were measured over 56 days after fertilizer application. Grass dry matter yields, when using CC and PP treatments, were not significantly different to the CAN treatment (p &amp;gt; 0.05). After reducing its salinity, AA also showed no differences to CAN on plant growth and the lowest coefficient of variation for dry matter yield as an indicator for yield stability. Accumulated N2O-emissions were lowest in the control and were 3-times higher in AA and CC compared to CAN (p &amp;lt; 0.05). If salinity levels are moderate, jellyfish application to soil can compete with artificial mineral fertilizers in terms of N-supply for above- and belowground yield response, regardless of jellyfish species used. However, elevated N2O-emissions are likely to affect its suitability for large-scale application. Nevertheless, if energy-efficient methods of drying and desalination of jellyfish can be developed, in coastal areas dried jellyfish is a valuable fertilizer in coastal areas, particularly in situations where nutrient supplies for agriculture are limited.

Open‐Path Dual‐Comb Spectroscopy for Multispecies Trace Gas Detection in the 4.5–5 µm Spectral Region

AbstractOpen‐path dual‐comb spectroscopy provides multispecies atmospheric gas concentration measurements with high precision. Here, open‐path dual‐comb spectroscopy is extended to the mid‐infrared 5 µm atmospheric window, enabling atmospheric concentration retrievals of the primary greenhouse gases, N2O, CO2, and H2O, as well as the criteria air pollutants O3 and CO across 600 m and 2 km round‐trip paths. Measurements are demonstrated over a five‐day period at 2 min temporal resolution with 80% uptime. The achieved precision is sufficient to resolve the atmospheric concentration variations of the multiple gas species; retrieved dry mixing ratios of CO and N2O are in good agreement with a colocated point sensor. In addition, the retrieved ratio of excess CO versus CO2 agrees with similar urban studies but disagrees with the US National Emission Inventory by a factor of 3. The retrieved ratio of excess N2O versus CO2 exhibits a plume‐dependent value, indicating the variability of sources of the greenhouse gas N2O.

Warming Shapes nirS- and nosZ-Type Denitrifier Communities and Stimulates N2O Emission in Acidic Paddy Soil.

Warming strongly stimulates soil nitrous oxide (N2O) emission, contributing to the global warming trend. Submerged paddy soils exhibit huge N2O emission potential; however, the N2O emission pathway and underlying mechanisms for warming are not clearly understood. We conducted an incubation experiment using 15N to investigate the dynamics of N2O emission at controlled temperatures (5, 15, 25, and 35°C) in 125% water-filled pore space. The community structures of nitrifiers and denitrifiers were determined via high-throughput sequencing of functional genes. Our results showed that elevated temperature sharply enhanced soil N2O emission from submerged paddy soil. Denitrification was the main contributor, accounting for more than 90% of total N2O emission at all treatment temperatures. N2O flux was coordinatively regulated by nirK-, nirS-, and nosZ-containing denitrifiers but not ammonia-oxidizing archaea or ammonia-oxidizing bacteria. The nirS-containing denitrifiers were more sensitive to temperature shifts, especially at a lower temperature range (5 to 25°C), and showed a stronger correlation with N2O flux than that of nirK-containing denitrifiers. In contrast, nosZ-containing denitrifiers exhibited substantial variation at higher temperatures (15 to 35°C), thereby playing an important role in N2O consumption. Certain taxa of nirS- and nosZ-containing denitrifiers regulated N2O flux, including nirS-containing denitrifiers affiliated with Rhodanobacter and Cupriavidus as well as nosZ-containing denitrifiers affiliated with Azoarcus and Azospirillum. Together, these findings suggest that elevated temperature can significantly increase N2O emission from denitrification in submerged paddy soils by shifting the overall community structures and enriching some indigenous taxa of nirS- and nosZ-containing denitrifiers. IMPORTANCE The interdependence between global warming and greenhouse gas N2O has always been the hot spot. However, information on factors contributing to N2O and temperature-dependent community structure changes is scarce. This study demonstrated high-temperature-induced N2O emission from submerged paddy soils, mainly via stimulating denitrification. Further, we speculate that key functional denitrifiers drive N2O emission. This study showed that denitrifiers were more sensitive to temperature rise than nitrifiers, and the temperature sensitivity differed among denitrifier communities. N2O-consuming denitrifiers (nosZ-containing denitrifiers) were more sensitive at a higher temperature range than N2O-producing denitrifiers (nirS-containing denitrifiers). This study's findings help predict N2O fluxes under different degrees of warming and develop strategies to mitigate N2O emissions from paddy fields based on microbial community regulation.

Sources of nitrous oxide from intensively managed pasture soils: the hole in the pipe

Rainfall and irrigation trigger large pulses of the powerful greenhouse gas N2O from intensively managed pastures, produced via multiple, simultaneously occurring pathways. These N2O pulses can account for a large fraction of total N2O losses, demonstrating the importance to determine magnitude and source partitioning of N2O under these conditions. This study investigated the response of different pathways of N2O production to wetting across three different textured pasture soils. Soil microcosms were fertilised with an ammonium nitrate (NH4NO3) solution which was either single or double 15N labelled, wetted to four different water-filled pore space (WFPS) levels, and incubated over two days. The use of a 15N pool mixing model together with soil N gross transformations enabled the attribution of N2O to specific pathways, and to express N2O emissions as a fraction of the underlying N transformation. Denitrification and nitrification mediated pathways contributed to the production of N2O in all soils, regardless of WFPS. Denitrification was the main pathway of N2O production accounting for >50% of cumulative N2O emissions even at low WFPS. The contribution of autotrophic nitrification to N2O emissions decreased with the amount of wetting, while the contribution of heterotrophic nitrification remained stable or increased. Following the hole-in-the-pipe model, 0.1%–4% of nitrified N was lost as N2O, increasing exponentially with WFPS, while the percentage of denitrified N emitted as N2O decreased, providing critical information for the representation of N2O/WFPS relationships in simulation models. Our findings demonstrate that the wetting of pasture soils promotes N2O production via denitrification and via the oxidation of organic N substrates driven by high carbon and N availability upon wetting. The large contribution of heterotrophic nitrification to N2O emissions should be considered when developing N2O abatement strategies, seeking to reduce N2O emissions in response to rainfall and irrigation from intensively managed pastures.

Flow regulates biological NO3− and N2O production in a turbid sub-tropical stream

Streams play a critical role in attenuating the excess reactive nitrogen (N) generated from human activities. Consequently, streams can also emit significant amounts of the potent greenhouse gas N2O. Models and manipulative experiments now suggest that hydrology regulates the balance between N removal and N2O production, but validating this hypothesis under field conditions has been difficult. We aimed to redress this knowledge gap by measuring changes in the concentration and isotopic composition of NO3− (δ18O-NO3−, δ15N-NO3−) and N2O (δ18O-N2O, δ15N-N2O, 15N-N2O site preference) in the sediments and surface water of a 30 m stream reach as discharge dropped from 2.7 to 1.8 m3 s−1. Over the eight-day measurement period the changes in conductivity, δ18O-H2O, and 222Rn indicated that hyporheic mixing decreased and net groundwater inputs increased as discharge declined. This coincided with increases in surface water NO3− (1–3 mg N l−1) and N2O (700–1000% saturation) that were beyond what could be explained by increased groundwater N inputs. Instead, both N2O and NO3− isotopic composition indicated that concentration increases were caused by increasing within-stream production (nitrification), rather than decreased reduction (denitrification), as hyporheic exchange decreased. This highlights the importance of oxidising processes in regulating N cycling even under strongly heterotrophic conditions (productivity/respiration: 0.005–0.2). Together these findings provide a first empirical confirmation that relatively short term (daily-weekly) stream flow dynamics directly regulate biological cycling of both NO3− and N2O.

Efficient Nitrification and Low-Level N2O Emission in a Weakly Acidic Bioreactor at Low Dissolved-Oxygen Levels Are Due to Comammox.

Nitrification is an essential process for nutrient removal from wastewater and an important emission source of nitrous oxide (N2O), which is a powerful greenhouse gas and a dominant ozone-depleting substance. In this study, nitrification and N2O emissions were tested in two weakly acidic (pH 6.3 to 6.8) reactors: one with dissolved oxygen (DO) at over 2.0 mg/liter and the other with DO at approximately 0.5 mg/liter. Efficient nitrification was achieved in both reactors. Compared to that in the high-DO reactor, N2O emission in the low-DO reactor decreased slightly, by 20%, and had insignificant correlation with the fluctuations of DO (P = 0.935) and nitrite (P = 0.713), indicating that N2O might not be produced mainly via nitrifier denitrification. Based on quantitative PCR (qPCR), quantitative fluorescent in situ hybridization (qFISH), and functional gene amplicon and metagenome sequencing, it was found that complete ammonia oxidizers (comammox), i.e., Nitrospira organisms, significantly outnumbered canonical ammonia-oxidizing bacteria (AOB) in both weakly acidic reactors, especially in the low-DO reactor with the comammox/AOB amoA gene ratio increasing from 6.6 to 17.1. Therefore, it was speculated that the enriched comammox was the primary cause for the slightly decreased N2O emission under long-term low DO in the weakly acidic reactor. This study demonstrated that the comammox Nitrospira can survive well under the weakly acidic and low-DO conditions, implying that achieving efficient nitrification with low N2O emission as well as low energy and alkalinity consumption is feasible for wastewater treatment.IMPORTANCE Nitrification in wastewater treatment is an important process for eutrophication control and an emission source for the greenhouse gas N2O. The nitrifying process is usually operated at a slightly alkaline pH and high DO (>2 mg/liter) to ensure efficient nitrification. However, it consumes a large amount of energy and chemicals, especially for wastewater without sufficient alkalinity. This paper demonstrates that comammox can adapt well to the weakly acidic and low-DO bioreactors, with a result of efficient nitrification and low N2O emission. These findings indicate that comammox organisms are significant for sustainable wastewater treatment, which provides an opportunity to achieve efficient nitrification with low N2O production as well as low energy and chemical consumption simultaneously.

Mechanism of N2O generation over chromium poisoned γ-Fe2O3 catalyst during selective catalytic reduction of NOx with NH3

Poisoning effect of Cr in flue gas on the remarkable generation of greenhouse gas N2O over γ-Fe2O3 catalyst during selective catalytic reduction of NOx with ammonia was firstly observed in this work. At low temperature, N2O generation over Cr poisoned γ-Fe2O3 catalyst was attributed to non-selective catalytic reduction (NSCR) of NOx. At high temperature, NSCR of NOx and ammonia peroxidation accompanying by weak NO disproportionation induced a more generation of N2O. The seeming promotion effect of Cr on NOx conversion of γ-Fe2O3 catalyst at low temperature was partly resulted from the NSCR of NO which also contributed to NOx conversion. At high temperature, the reduction of NOx to innocent N2 was far inhibited after chromium poisoning in view of the low selectivity of NO to N2. The formed FeCr2O4 in chromium poisoned γ-Fe2O3 catalyst was the induction factor for large N2O production, which enhanced the acidity and reducibility of catalyst. Transient DRIFTS results indicated that SCR and NSCR of NOx over chromium poisoned γ-Fe2O3 catalyst predominantly happened via Eley-Rideal mechanism. Moreover, O2 in flue gas determined the activation of adsorbed NH3 and which dictated the NSCR of NOx and ammonia peroxidation.

Nitrous oxide emissions, N uptake, biomass, and rubber yield in N-fertilized, surface-irrigated guayule

Nitrous oxide (N2O) emissions from N fertilizer applied to row crops makes up a large portion of the greenhouse gas loading to the atmosphere. Guayule (Parthenium argentatum A. Gray) is a desert perennial shrub being promoted for Central Arizona farmers as a source of natural rubber and hypoallergenic latex. Emissions of the greenhouse gas N2O and crop N uptake have not been previously quantified in this multi-year cropping system. A 2.5-year study was conducted on transplanted and surface-irrigated guayule on a Casa Grande sandy loam in Maricopa, AZ to assess the agronomic and environmental responses to N fertilizer application rate. Four N fertilizer rates ranging from 0 to 252 kg N ha−1 were applied as ammonium sulfate in three splits. Nitrous oxide emissions were measured with 1-L vented chambers 34 times over 98 weeks from 17 April 2013 to 6 March 2015 with pauses during winter dormant seasons. Nitrogen rate significantly affected N2O emissions, which ranged from 1.2 to 4.5 kg N ha−1 for the 0 and 252 kg N ha−1 fertilizer rates. Emission factors were 1.5, 1.4, and 1.3 % of the added ammonium sulfate-N emitted as N2O for 84, 168, and 250 kg N ha−1, respectively, which are in the range of those for other better-studied crops such as corn (Zea mays L.) and cotton (Gossypium hirsutum L.) Nitrogen uptake by guayule averaged 191 kg N ha−1 for biomass and rubber yields of 19 Mg ha−1 and 1070 kg ha−1, respectively. There was no effect of N rate on N uptake, biomass, or rubber yields because of initial soil profile nitrate (NO3) levels of 85–150 kg NO3-N ha−1. A N balance of inputs (initial soil NO3, N fertilizer, NO3-N added in irrigation) and outputs (N uptake, N2O, and dinitrogen (N2) emissions) was constructed. Unaccounted-for N was apparently lost as NO3 leaching below the root zone. In conclusion, the informative N2O emissions data presented are the first for guayule, and the N uptake levels reported here can be used in updated, improved N fertilizer recommendations for guayule.