Major Source Of NO Research Articles

Investigating atmospheric nitrate sources and formation pathways between heating and non-heating seasons in urban North China

In urban North China, nitrate () is a primary contributor to haze formation. So far, the production processes and source apportionments of atmospheric during the heating season (i.e. the wintertime) have not yet been well understood. This study determined δ15N–, δ18O–, and Δ17O– of aerosol samples to compare the potential sources and formation pathways of atmospheric during heating (November to March) and non-heating (April to May) seasons. Combining stable isotope composition with the MixSIAR model based on Δ17O– showed that NO3 + DMS/HC (dimethyl sulfate/hydrocarbon) pathway was the dominant process of atmospheric nitrate formation during the heating season (mean = 52.88 ± 16.11%). During the non-heating season, the contributions of NO3 + DMS/HC (mean = 37.89 ± 13.57%) and N2O5 + H2O (mean = 35.24 ± 3.75%) pathways were comparable. We found that Δ17O– was negatively correlated with wind speed and positively correlated with relative humidity during the heating season, possibly associated with the sources and production of atmospheric . In specific, in a dust storm event, the very low Δ17O– is likely associated with particles from land surface. Under the premise of considering 15N fractionation, the constraint-based on δ15N– illustrated that coal combustion was the major source of NO x emission during the heating season, and the relative contribution of coal combustion decreased rapidly from the heating season (mean = 42.56 ± 15.50%) to the non-heating season (mean = 21.86 ± 4.91%). Conversely, the proportion of NOx emitted by soil microbes rose significantly from the heating (mean = 9.67 ± 5.99%) to non-heating season (mean = 24.02 ± 11.65%). This study revealed differences in the sources and formation processes of atmospheric during the heating and non-heating seasons, which are of significance to atmospheric nitrogen oxide/nitrate pollution mitigation.

Release of nitric oxide by the Escherichia coli YtfE (RIC) protein and its reduction by the hybrid cluster protein in an integrated pathway to minimize cytoplasmic nitrosative stress

Synthesis of the Escherichia coli YtfE protein, also known as RIC, for the repair of damaged iron centres, is highly induced during anaerobic growth under conditions of nitrosative stress. How YtfE repairs nitrosative damage remains unclear. Contrary to previous reports, we show that strains defective in YtfE that lack the high-affinity NO reductase activity of the hybrid cluster protein (Hcp) are less sensitive to nitrosative stress than isogenic ytfE+ strains, which are extremely sensitive. Evidence that this sensitivity is due to YtfE-dependent release of NO into the cytoplasm includes: relief of growth inhibition by PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide), which degrades NO; relief of nitrosative stress by deletion of narG encoding the nitrate reductase that is the major source of NO from nitrite; partial suppression of nitrosative stress due to loss of Hcp function by a further mutation in ytfE; YtfE-dependent loss of aconitase and fumarase activities in the absence of Hcp; and YtfE-dependent relief of NsrR repression of the hcp promoter in response to cytoplasmic NO. We suggest that a major role for YtfE is to reverse nitrosative damage by releasing, directly or indirectly, NO from nitrosylated proteins into the cytoplasm where the high-affinity NO reductase activity of Hcp ensures its reduction to N2O. If so, the concerted action of YtfE and Hcp would not only maintain the cytoplasmic concentration of NO in the low nM range, but also provide a rationalization for the coordinate regulation of Hcp and YtfE synthesis by NsrR.

Agricultural soils are major source of NO x emission

Air pollution regulations that are focused on cars and trucks have helped clean up the air in California’s cities, but rural areas still struggle with poor air quality. Agricultural soils may be an overlooked source of as much as half of California’s emissions of nitric oxide and nitrogen dioxide, collectively called NOx, new research suggests. NOx compounds contribute to smog and can cause lung damage. Previous field studies suggested that heavily fertilized soils might emit significant amounts of NOx, but work led by Maya Almaraz of the University of California, Davis, is the first to provide a state-scale estimate. Almaraz and colleagues modeled soil emissions computationally and correlated them with airborne NOx measurements (Sci. Adv. 2018, DOI: 10.1126/sciadv.aao3477). They found that agricultural soils likely contribute 20–51% of NOx in California’s air; emissions were particularly high over the San Joaquin Valley. “The effect of large soil NOx emissions on air quality

Agriculture is a major source of NO x pollution in California.

Nitrogen oxides (NO x = NO + NO2) are a primary component of air pollution-a leading cause of premature death in humans and biodiversity declines worldwide. Although regulatory policies in California have successfully limited transportation sources of NO x pollution, several of the United States' worst-air quality districts remain in rural regions of the state. Site-based findings suggest that NO x emissions from California's agricultural soils could contribute to air quality issues; however, a statewide estimate is hitherto lacking. We show that agricultural soils are a dominant source of NO x pollution in California, with especially high soil NO x emissions from the state's Central Valley region. We base our conclusion on two independent approaches: (i) a bottom-up spatial model of soil NO x emissions and (ii) top-down airborne observations of atmospheric NO x concentrations over the San Joaquin Valley. These approaches point to a large, overlooked NO x source from cropland soil, which is estimated to increase the NO x budget by 20 to 51%. These estimates are consistent with previous studies of point-scale measurements of NO x emissions from the soil. Our results highlight opportunities to limit NO x emissions from agriculture by investing in management practices that will bring co-benefits to the economy, ecosystems, and human health in rural areas of California.

Evaluating the Sources and Fate of Nitrate in the Alluvial Aquifers in the Shijiazhuang Rural and Suburban Area, China: Hydrochemical and Multi-Isotopic Approaches

The identification of the sources and fate of NO\(_{3}^{-}\) contaminants is important to protect the water quality of aquifer systems. In this study, NO\(_{3}^{-}\) contaminated groundwater from the drinking water wells in the Shijiazhuang area, China, was chemically (NO\(_{3}^{-}\)/Cl\(^{\rm{{-}}}\) ratio) and isotopically (\(δ\)\(^{\rm{15}}\)N\(_{\rm{NO3}}\), \(\delta\)\(^{\rm{18}}\)O\(_{\rm{NO3}}\) and \(\delta\)\(^{\rm{13}}\)C\(_{\rm{DOC}}\); \(\delta\)\(^{\rm{2}}\)H\(_{\rm{H2O}}\), \(\delta\)\(^{\rm{18}}\)O\(_{\rm{H2O}}\)) characterized to identify the sources of NO\(_{3}^{-}\) and address subsequent biogeochemical processes. The positive correlations between dominant anions and cations suggested that the dissolution of calcium carbonate and gypsum minerals was the most effective process in the groundwater. Elevated concentrations of NO\(_{3}^{-}\), Cl\(^{\rm{{-}}}\) and Mg\(^{\rm{2+}}\) could be related to the wastewater irrigation and usage of fertilizers. The natural water in the study area originated primarily from precipitation and experienced a limited extent of evaporation, as demonstrated by measurements of \(\delta\)\(^{\rm{2}}\)H\(_{\rm{H2O}}\) and \(\delta\)\(^{\rm{18}}\)O\(_{\rm{H2O}}\). A cross-plot of \(\delta\)\(^{\rm{15}}\)N\(_{\rm{NO3}}\) vs. \(\delta\)\(^{\rm{18}}\)O\(_{\rm{NO3}}\) gave an enrichment of the 15N isotope relative to the 18O isotope by a factor of 2. A further insight into the denitrification process was obtained by the synergistic changes in \(\delta\)\(^{\rm{13}}\)C\(_{\rm{DOC}}\) and \(\delta\)\(^{\rm{15}}\)N\(_{\rm{NO3}}\) values, confirming that a low extent of denitrification occurred. Nitrification processes were evaluated by means of \(\delta\)\(^{\rm{18}}\)O\(_{\rm{NO3}}\) and \(\delta\)\(^{\rm{18}}\)O\(_{\rm{H2O}}\). The initial \(\delta\)\(^{\rm{15}}\)N\(_{\rm{NO3}}\) value(s) of the NO\(_{3}^{-}\) source(s) were roughly estimated between 2‰ and 5‰. Based on the level of natural NO\(_{3}^{-}\), anthropogenic activities were considered the main reason for the elevated NO\(_{3}^{-}\) concentration of the shallow groundwater. NH\(_{4}^{+}\) fertilizers were the major source of NO\(_{3}^{-}\) in the non-wastewater irrigated area, while wastewater was regarded as the primary source of NO\(_{3}^{-}\) in the wastewater-irrigated area. A low content of NO\(_{3}^{-}\) in deep groundwater might mainly be influenced by precipitation and soil organic N that was involved in denitrification reactions. Some of the deep groundwater samples could have been contaminated by wastewater. The mixing process of multiple NO\(_{3}^{-}\) sources was identified as another important factor affecting the NO\(_{3}^{-}\) concentration of the groundwater in the study area. The combined use of \(\delta\)\(^{\rm{15}}\)N\(_{\rm{NO3}}\), \(\delta\)\(^{\rm{18}}\)O\(_{\rm{NO3}}\) and \(\delta\)\(^{\rm{13}}\)C\(_{\rm{DOC}}\) results and hydrochemical data (NO\(_{3}^{-}\)/Cl\(^{\rm{{-}}}\) ratios) gives an insight into the mixing effect of different NO\(_{3}^{-}\) sources and processes affecting NO\(_{3}^{-}\) concentration under conditions of intensive land-use activities.

Dynamics of nitrate and chloride during storm events in agricultural catchments with different subsurface drainage intensity (Indiana, USA)

Summary Drainage tiles buried beneath many naturally poorly drained agricultural fields in the Midwestern U.S. are believed to “short circuit” pools of NO 3 - -laden soil water and shallow groundwater directly into streams that eventually discharge to the Mississippi River. Although much is known about the mechanisms controlling this regionally pervasive practice of artificial drainage at the field-plot scale, an integrative assessment of the effect of drainage density (i.e., the number of tile drains per unit area) on the transport of nutrients and solutes in streams at the catchment scale is lacking. In this study, we quantified the flux and hydrological pathways of agricultural NO 3 - and road-salt Cl− from catchments lying within the Wabash River Basin, a major source of NO 3 - to the Mississippi River. The paired catchments differ primarily in drainage density (70% vs. 31%, by catchment area), with essentially all other agricultural management, land use, and soil drainage characteristics remaining equal. Our study revealed two significant hydrological responses to increased drainage density: (1) more near-surface storm event water (dilute in both NO 3 - and Cl - ) was transported early in the storm and (2) higher transport of Cl−-laden pre-event soil water relative to shallow groundwater elevated in NO 3 - occurred later in the storm. These patterns are consistent with a proposed conceptual model in which increased drainage density results in (1) greater transport of soil water to streams and (2) a delayed rise in the water table. With respect to nutrient management implications, these results indicate that increased drainage density impacts subsurface pools of Cl− and NO 3 - differently, a finding that we propose is linked to soil/ground water dynamics in artificially drained agricultural catchments.

Unresolved sources, sinks, and pathways for the recovery of enteric bacteria from nitrosative stress

Major questions concerning the sources and mechanisms of the reduction of nitric oxide by enteric bacteria remain unresolved. The membrane-associated nitrate reductase is the major source of NO generated from nitrite, but at least one other source remains to be identified. Nitrite reductases are primarily detoxification systems that decrease rather than increase the accumulation of NO in the cytoplasm. Whether they also catalyze NO formation is unresolved. The FNR protein that regulates transitions between aerobic and anaerobic growth is inactivated as a consequence of nitrosative damage, but we challenge the idea that FNR is a physiologically relevant sensor of NO, except under the most severe nitrosative stress. As none of the three enzymes that reduce NO account for the majority of the rate of NO reduction, additional mechanisms remain to be discovered. Little is known about the biochemistry of damage repair. Whatever the growth conditions and however severe the nitrosative stress, groups of proteins are synthesized to protect the bacterial cytoplasm against the side effects of nitrate and nitrite reduction. The enigmatic hybrid cluster protein is more likely to be part of a repair pathway than a hydroxylamine reductase, as annotated in many genome databases.

The influence of light on nitrogen cycling and the primary nitrite maximum in a seasonally stratified sea

In the seasonally stratified Gulf of Aqaba Red Sea, both NO 2 - release by phytoplankton and NH 4 + oxidation by nitrifying microbes contributed to the formation of a primary nitrite maximum (PNM) over different seasons and depths in the water column. In the winter and during the days immediately following spring stratification, NO 2 - formation was strongly correlated ( R 2 = 0.99) with decreasing irradiance and chlorophyll, suggesting that incomplete NO 3 - reduction by light limited phytoplankton was a major source of NO 2 - . However, as stratification progressed, NO 2 - continued to be generated below the euphotic depth by microbial NH 4 + oxidation, likely due to differential photoinhibition of NH 4 + and NO 2 - oxidizing populations. Natural abundance stable nitrogen isotope analyses revealed a decoupling of the δ 15N and δ 18O in the combined NO 3 - and NO 2 - pool, suggesting that assimilation and nitrification were co-occurring in surface waters. As stratification progressed, the δ 15N of particulate N below the euphotic depth increased from −5‰ to up to +20‰. N uptake rates were also influenced by light; based on 15N tracer experiments, assimilation of NO 3 - , NO 2 - , and urea was more rapid in the light (434 ± 24, 94 ± 17, and 1194 ± 48 nmol N L −1 day −1 respectively) than in the dark (58 ± 14, 29 ± 14, and 476 ± 31 nmol N L −1 day −1 respectively). Dark NH 4 + assimilation was 314 ± 31 nmol N L −1 day −1, while light NH 4 + assimilation was much faster, resulting in complete consumption of the 15N spike in less than 7 h from spike addition. The overall rate of coupled urea mineralization and NH 4 + oxidation (14.1 ± 7.6 nmol N L −1 day −1) was similar to that of NH 4 + oxidation alone (16.4 ± 8.1 nmol N L −1 day −1), suggesting that mineralization of labile dissolved organic N compounds like urea was not a rate limiting step for nitrification. Our results suggest that assimilation and nitrification compete for NH 4 + and that N transformation rates throughout the water column are influenced by light over diel and seasonal cycles, allowing phytoplankton and nitrifying microbes to contribute jointly to PNM formation. We identify important factors that influence the N cycle throughout the year, including light intensity, substrate availability, and microbial community structure. These processes could be relevant to other regions worldwide where seasonal variability in mixing depth and stratification influence the contributions of phytoplankton and non-photosynthetic microbes to the N cycle.

Nitric oxide from nitrite reduction by hemoglobin in the plasma and erythrocytes

Experimental evidence has shown that nitrite anion plays a key role in one of the proposed mechanisms for hypoxic vasodilation, in which the erythrocyte acts as a NO generator and deoxygenated hemoglobin in pre-capillary arterioles reduces nitrite to NO, which contributes to vascular smooth muscle relaxation. However, because of the complex reactions among nitrite, hemoglobin, and the NO that is formed, the amount of NO delivered by this mechanism under various conditions has not been quantified experimentally. Furthermore, paracrine NO is scavenged by cell-free hemoglobin, as shown by studies of diseases characterized by extensive hemolysis (e.g., sickle cell disease) and the administration of hemoglobin-based oxygen carriers. Taking into consideration the free access of cell-free hemoglobin to the vascular wall and its ability to act as a nitrite reductase, we have now examined the hypothesis that in hypoxia this cell-free hemoglobin could serve as an additional endocrine source of NO. In this study, we constructed a multicellular model to characterize the amount of NO delivered by the reaction of nitrite with both intraerythrocytic and cell-free hemoglobin, while intentionally neglecting all other possible sources of NO in the vasculature. We also examined the roles of hemoglobin molecules in each compartment as nitrite reductases and NO scavengers using the model. Our calculations show that: (1) ∼0.04 pM NO from erythrocytes could reach the smooth muscle if free diffusion were the sole export mechanism; however, this value could rise to ∼43 pM with a membrane-associated mechanism that facilitated NO release from erythrocytes; the results also strongly depend on the erythrocyte membrane permeability to NO; (2) despite the closer proximity of cell-free hemoglobin to the smooth muscle, cell-free hemoglobin reaction with nitrite generates approximately 0.02 pM of free NO that can reach the vascular wall, because of a strong self-capture effect. However, it is worth noting that this value is in the same range as erythrocytic hemoglobin-generated NO that is able to diffuse freely out of the cell, despite the tremendous difference in hemoglobin concentration in both cases (μM hemoglobin in plasma vs. mM in erythrocyte); (3) intraerythrocytic hemoglobin encapsulated by a NO-resistant membrane is the major source of NO from nitrite reduction, and cell-free hemoglobin is a significant scavenger of both paracrine and endocrine NO.

Clinical and pathological features of fat embolism with acute respiratory distress syndrome

FES (fat embolism syndrome) is a clinical problem, and, although ARDS (acute respiratory distress syndrome) has been considered as a serious complication of FES, the pathogenesis of ARDS associated with FES remains unclear. In the present study, we investigated the clinical manifestations, and biochemical and pathophysiological changes, in subjects associated with FES and ARDS, to elucidate the possible mechanisms involved in this disorder. A total of eight patients with FES were studied, and arterial blood pH, PaO(2) (arterial partial pressure of O(2)), PaCO(2) (arterial partial pressure of CO(2)), biochemical and pathophysiological data were obtained. These subjects suffered from crash injuries and developed FES associated with ARDS, and each died within 2 h after admission. In the subjects, chest radiography revealed that the lungs were clear on admission, and pulmonary infiltration was observed within 2 h of admission. Arterial blood pH and PaO(2) declined, whereas PaCO(2) increased. Plasma PLA(2) (phospholipase A(2)), nitrate/nitrite, methylguanidine, TNF-alpha (tumour necrosis factor-alpha), IL-1beta (interleukin-1beta) and IL-10 (interleukin-10) were significantly elevated. Pathological examinations revealed alveolar oedema and haemorrhage with multiple fat droplet depositions and fibrin thrombi. Fat droplets were also found in the arterioles and/or capillaries in the lung, kidney and brain. Immunohistochemical staining identified iNOS (inducible nitric oxide synthase) in alveolar macrophages. In conclusion, our clinical analysis suggests that PLA(2), NO, free radicals and pro-inflammatory cytokines are involved in the pathogenesis of ARDS associated with FES. The major source of NO is the alveolar macrophages.

Nitric oxide and cnidarian bleaching: an eviction notice mediates breakdown of a symbiosis

Nitric oxide (NO) is a free radical implicated in numerous cell signaling, physiological and pathophysiological processes of eukaryotic cells. Here, we describe the production of NO as part of the cellular stress response of the symbiotic sea anemone Aiptasia pallida, which hosts dinoflagellates from the genus Symbiodinium. We show that exposure to elevated temperatures induces symbiotic anemones to produce high levels of NO, leading to the collapse of the symbiosis. These results shed light on the poorly understood cellular mechanism through which elevated seawater temperature causes the release of symbiotic algae from symbiotic cnidarians, a detrimental process known as coral (cnidarian) bleaching. The results presented here show that the host cell is a major source of NO during exposure to elevated temperatures and that this constitutes a cytotoxic response leading to bleaching. These results have important evolutionary implications as the observed NO production in these basal metazoans displays many parallels to the cytotoxic inflammatory response to pathogens, a well-understood process in mammalian model systems.

High-resolution spatial patterns of long-term mean concentrations of air pollutants in Haifa Bay area

High-resolution maps of the mean concentrations of SO 2 , NO, NO 2 , O 3 , and PM 10 in the period 2002–2004 were produced using half-hourly data from the local air quality monitoring network in Haifa Bay area, Israel. The network consists of 20 monitoring stations within an area of 206 km 2 , which encompasses a major industrial and power generation centre in the midst of a population of about 500 000. The pollutants’ spatial features agree well with their known sources and the expected dispersion by the prevailing meteorology. The ranking of their spatial variations agree with published observations on larger spatial scales. The high-resolution maps capture in a small spatial scale the NO x and O 3 cycle relationships expected by theory, and previously observed by analyses of monitoring time series. High correlation was found between the spatial patterns of the PM 10 , NO x and O 3 , whereas the correlation between the spatial features of the PM 10 and SO 2 is low. This suggests that the traffic, a major source of NO x , rather than industry, the major source of SO 2 , is the main contributor to the anthropogenic PM 10 in the study area. This inference is corroborated by the low sulphur to nitrogen ratio throughout the region, which is typical of traffic-dominated pollution. A general conclusion drawn from this study is that high-resolution monitoring and mapping can significantly contribute to air quality management programmes in terms of both pollution abatement and exposure and risk assessment.

Emissions of Particulate and Gaseous Pollutants within the Keelung Harbor Region of Taiwan

The Keelung port, which is located on the northern tip of Taiwan, right next to the Taipei metropolitan area, is an important international harbor. However, any air pollutants generated from the Keelung port region, immediately travel to the neighboring Keelung city, and greatly impact the residents' daily life and the quality of their environment. This study has investigated and quantified pollution emissions, from the Keelung port region, between 1997 and 2002. Emissions from major air pollution sources were estimated. The estimated results indicated that total TSP (total suspended particles) emissions had significantly increased, from 5221 ton/yr in 1997 to 262 687 ton/yr in 2002, due to the greatly increased volume of sand imported into Keelung Harbor. Quantities of other emissions, such as SO(2), NO(2), CO and HC remained stable and were 440, 207, 78 and 25 ton/yr, respectively, on average, with variations within 7% over the previous six-year period. By examining the emissions from pollution sources, it was found that TSP emissions mainly originated from re-suspension of dust, due to both vehicle movement and the sand unloading process; this accounted for over 99% of the total TSP emissions produced in the port region. About 80% of the total SO(2) emissions originated from the main ships' engines within the Keelung port region, due to the use of fuel with a high sulfur content. In addition, loading/unloading machines within the port region were the major sources of NO(2), CO and HC pollution emissions, which comprised 54, 58 and 66% of the total emissions of these pollutants, respectively. TSP emissions from Keelung port were much higher than from the neighboring Keelung city; hence, alleviating TSP emissions should be the first priority for air pollution reduction within both the port of Keelung and Keelung city.

Denitrification in sediments of the Laurentian Trough, St. Lawrence Estuary, Québec, Canada

The isotope pairing technique was used to obtain the first sedimentary denitrification rates for the St. Lawrence Estuary/Gulf system (Québec, Canada). Denitrification rates were measured on intact sediment cores collected at three stations down the slope of the Laurentian Trough at 103, 200 and 320 m depth. For samples collected in June 1997, total denitrification rates ranged from 1.8 to 3.3 μmol N m −2 h −1 among the three stations. Only 3–5% of the NO 3 − consumed by the sediments was subsequently denitrified. Nitrification was the major source of NO 3 − for denitrification, representing 56–79% of total denitrification rates. Sediment consumption of water column O 2 (102–187 μmol O 2 m −2 h −1) and NO 3 − (13.9–25.5 NO 3 − m −2 h −1) increased significantly downslope, as did total denitrification rates. Denitrification made a negligible (<0.2%) contribution to carbon mineralization in our cores, but may have a greater impact on the nitrogen cycle. In addition, data suggest the presence of a major dissimilatory nitrate sink in these sediments that far exceeds the requirements of denitrification. The latter observation is considered in terms of proposed interactions between the nitrogen cycle and metal reduction/oxidation. We conclude by considering limitations to the extrapolation of these data to annual and regional scale nitrogen budgets for the deep waters of the St. Lawrence Estuary.

Differences in nitric oxide production: a comparison of retinal ganglion cells and retinal glial cells cultured under hypoxic conditions

The aim of this study was to compare the effects of hypoxia on nitric oxide synthase (NOS) expression and the production of NO between isolated retinal ganglion cells (RGCs) and retinal glial cells. Reverse transcription-polymerase chain reaction (RT-PCR) was employed to examine the presence of neuronal NOS mRNA, inducible NOS mRNA, and endothelial NOS mRNAs in the two cell types. RGCs and retinal glial cells were separately cultured under hypoxic (10% O 2) or control (20% O 2) conditions. Changes in NOS-mRNA expression were quantified by real-time PCR, and nitrite in the medium was measured up to 96 h of culture. The effects of non-NOS- and iNOS-selective inhibitors on hypoxia-induced release of nitrite in the culture medium were evaluated. RT-PCR revealed the presence of three types of NOSs in the two types of cultured cells. Hypoxic culture conditions significantly changed the expression of all NOS mRNAs in retinal glial cells but not in RGCs. NO production showed significant changes corresponding to those of NOS mRNAs in retinal glial cells but not in RGCs, and both NOS inhibitors significantly reduced hypoxia-induced nitrite release in retinal glial cells. Retinal glial cells but not RGCs may be the major source of NO under hypoxic conditions.

Catalytic abatement of nitrogen oxides–stationary applications

Emission regulations for unburned hydrocarbons, nitrogen oxides and particulates are becoming more stringent throughout the world. Nitrogen oxides include NO, NO 2 and N 2O. Transportation (mobile source) and fuel combustion (stationary source) are the main sources of nitrogen oxide emissions [1]. This review will update the commercial catalytic applications for abating nitrogen compounds (including nitrogen oxides) and will summarize the status of the following technologies applied to stationary source emissions: (1) selective catalytic reduction of NO x using ammonia (SCR); (2) non-selective catalytic reduction of NO x (NSCR); (3) nitrous oxide (N 2O) decomposition; and (4) ammonia (NH 3) decomposition. The major sources of NO x from stationary sources are power generation, stationary engines, industrial boilers, process heaters and gas turbines [2]. SCR is usually applied to all these sources and NSCR is applied mainly to the stationary engines. N 2O decomposition is used mainly in the chemical industry associated with nylon intermediate manufacture. NH 3 decomposition is a fairly new application and can be applied to SCR to decompose NH 3 emissions from industrial operations.

Direct measurement of nitric oxide generation from nitric oxide synthase.

Although nitric oxide synthase (NOS) is widely considered as the major source of NO in biological cells and tissues, direct evidence demonstrating NO formation from the purified enzyme has been lacking. It was recently reported that NOS does not synthesize NO, but rather generates nitroxyl anion (NO-) that is subsequently converted to NO by superoxide dismutase (SOD). To determine if NOS synthesizes NO, electron paramagnetic resonance (EPR) spectroscopy was applied to directly measure NO formation from purified neuronal NOS. In the presence of the NO trap Fe2+-N-methyl-D-glucamine dithiocarbamate, NO gives rise to characteristic EPR signals with g = 2.04 and aN = 12.7 G, whereas NO- is undetectable. In the presence of L-arginine (L-Arg) and cofactors, NOS generated prominent NO signals. This NO generation did not require SOD, and it was blocked by the specific NOS inhibitor N-nitro-L-arginine methyl ester. Isotope-labeling experiments with L-[15N]Arg further demonstrated that NOS-catalyzed NO arose from the guanidino nitrogen of L-Arg. Measurement of the time course of NO formation demonstrated that it paralleled that of L-citrulline. The conditions used in the prior study were shown to result in potent superoxide generation, and this may explain the failure to measure NO formation in the absence of SOD. These experiments provide unequivocal evidence that NOS does directly synthesize NO from L-Arg.

Chemistry of the nightside ionosphere of Mars

The chemistry of seven ions, O2+, NO+, CO2+, O+, N2+, CO+, and H+, is studied in the nightside ionosphere of Mars using the analytical yield spectrum approach and coupled continuity equations for the steady state condition. The source and sink processes of these ions are discussed in detail. We have found that the nightside Martian ionosphere produced due to precipitation of magnetotail electrons agrees with the Viking observations rather than other sources of ionization such as the precipitation of plasma sheet electron or horizontal plasma transport from dayside ionosphere to the nightside similar to that operating on Venus, The precipitation of magnetotail electron produces major ion CO2+ which is quickly removed by the reactions (1) CO2+ + O → O2+ + CO, (2) CO2+ + O → O+ + CO2 and (3) O+ + CO2 → O2+ + CO leading to O2+ as a dominant ion in the nightside ionosphere of Mars. The reactions of O+ with N and NO are the major sources of NO+, which is lost entirely by dissociative recombination reaction. The second reaction is the major source of O+ below 190 km. Above this altitude the magnetotail electron impact ionization process is an important source of O+. This process is also important for the production of CO+ and N2+. The ion O+ is destroyed by the third reaction, while CO+ and N2+ are destroyed by charge transfer reaction with CO2. The ion H+ is produced due to charge exchange reaction between O+ and H which is lost by CO2.

Airborne nitric oxide: Inflammatory marker and aerocrine messenger in man.

1. In healthy subjects, exhaled NO originates mainly from the upper airways with only a minor contribution from the lower airways and the lungs. A large NO production takes place in the epithelium of the paranasal sinuses and this NO contributes considerably to the levels of NO found in nasally exhaled air. Immunohistochemical and mRNA in situ hybridisation studies suggest that sinus NO synthase is identical or very closely related to the human iNOS. Furthermore, the NOS activity in sinus mucosa is mostly Ca(2+)-independent. However, the regulation of sinus NOS expression seems to differ fundamentally from what has earlier been described for iNOS. Thus, sinus NOS is constitutively expressed and seems resistant to steroids. The high local NO concentrations in the nasal airways and the sinuses may help to protect against airborne infectious agents. Thus, airborne NO may represent the very first line of defence in the airways, possibly acting on pathogens even before they reach the mucosa. 2. Nasal concentrations of NO are markedly reduced in children with Kartagener's syndrome and in patients with CF. A simple chemiluminescence test test could be of help in early non-invasive diagnosis of these chronic airway diseases. 3. Inhaled endogenous NO, derived from the upper airways, may be involved in regulation of pulmonary function in man. NO will reach the lower airways and the lungs with the inspired air and at levels that are especially high during nasal breathing. This NO may act by enhancing blood flow preferentially in well ventilated areas of the lung, thus optimizing ventilation/perfusion matching. The involvement of autogenous NO in regulation of pulmonary function may represent a novel physiological principle, namely that of an enzymatically produced airborne messenger. The term "aerocrine" may be appropriate for this action of NO in the airways. These findings may also help to explain one biological role of the enigmatic human paranasal sinuses, the major sources of NO in the upper airways. 4. A continuous production of NO takes place in the acidic stomach through chemical reduction of nitrite present in swallowed saliva. This is the first evidence of non-enzymatic NO production in humans. Stomach NO may be involved in local defence against swallowed pathogens and in regulation of superficial mucosal blood flow and mucus production. 5. Luminal concentrations of NO are increased in the lower airways of asthmatic children, in the colon of patients with inflammatory bowel disease, and in the urinary bladder of patients with cystitis. Local steroid treatment reduces orally exhaled NO levels in asthmatic children. Nasal NO levels did not differ between controls and asthmatic children with or without concomitant allergic rhinitis. In conclusion, nitric oxide found in exhaled air originates mainly in the upper airways. A large production of NO takes place in the paranasal sinuses from a constitutively-expressed, steroid-resistant "inducible-like" NO synthase in the epithelial cells. Sinus NO contributes substantially to levels of NO found in nasally exhaled air. Sinus NO may have a dual function. First, the very high concentrations in the sinuses may contribute to local host defence. Second, when diluted in the inhaled air, sinus-derived NO may act as an "aerocrine" messenger, with distal effects on pulmonary blood flow and oxygen uptake. Intubated patients are deprived of autogenous NO from the upper airways and might benefit from substitution. Measurements of local NO production in hollow organs may be done easily by analysing the concentrations of NO gas in luminal air. Such noninvasive methods may be useful not only to explore the role of NO in inflammation and host defence, but also in the diagnosis and monitoring of inflammatory mucosal diseases such as asthma, ulcerative colitis and cystitis. Thus, airborne NO may be looked upon as a marker of inflammation and as an aerocrine messenger in humans.

The magnitude and persistence of soil NO, N2O, CH4, and CO2 fluxes from burned tropical savanna in Brazil

Among all global ecosystems, tropical savannas are the most severely and extensively affected by anthropogenic burning. Frequency of fire in cerrado, a type of tropical savanna covering 25% of Brazil, is 2 to 4 years. In 1992 we measured soil fluxes of NO, N2O, CH4, and CO2 from cerrado sites that had been burned within the previous 2 days, 30 days, 1 year, and from a control site last burned in 1976. NO and N2O fluxes responded dramatically to fire with the highest fluxes observed from newly burned soils after addition of water. Emissions of N‐trace gases after burning were of similar magnitude to estimated emissions during combustion. NO fluxes immediately after burning are among the highest observed for any ecosystem studied to date. These rates declined with time after burning and had returned to control levels 1 year after the burn. An assessment of our data suggested that tropical savanna, burned or unburned, is a major source of NO to the troposphere. Cerrado appeared to be a minor source of N2O and a sink for atmospheric CH4. Burning also elevated CO2 fluxes, which remained detectably elevated 1 year later.