Main Source Of NO Research Articles

Nutrient dynamics in a chronosequence of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) stands on the Beaujolais Mounts (France). 1: Qualitative approach

Nutrient dynamics along a rotation of Douglas-fir was studied by chemical characterisation of solutions that are transferred through the ecosystem. The chronosequence approach was used to represent the development stages of the forest rotation. Rainfall composition classified the present site as a pristine area. The transfer of precipitations through canopies was characterised by an enrichment of the ionic charge in the solutions, which was related to the washoff of elements deposited on branches and needles (dry deposits) or to the ion-exchange processes between the elements in the internal plant parts and those in the rainfall (canopy leaching). The main source of NO 3 − N, NH 4 + N, SO 4 2− S, Cl −, Na +, Ca 2+, Mg 2+, Al 3+ and H + was considered to be the washoff from plant surfaces. Total organic carbon (TOC), K + and Mn 2+ were considered to originate mainly from leaching. The foliar uptake of nitrogen in the young stand and the parallel leaching of K + from the canopy characterised differences in solution composition between the stands. The concentration increase was more significant in stemflow solutions than in throughfall as a consequence of the input of elements from the bole surface washoff. Differences between stands were related to stem size and to exposure of stems to the deposition of particles and gases. SO 4 2− S, NO 3 − N and Cl − controlled the transfer of nutrients in rainfall, throughfall and stemflow to the same extent. A higher participation of SO 4 2− S in the ionic charge was mainly observed during winter. Soil solution chemistry was the result of a complex combination of factors like soil organic matter content, mineralisation and nitrification capacity and plant nutrient requirement, and was greatly influenced by stand structure and seasonal patterns. The soil organic pool and its potential for mineralisation were the main factors that determined the solution chemistry in all layers, but to different extents. Nitrification was the major process acting on the release of cations from the ion-exchange sites and NO 3 − N was generally the main anion in the soil solutions. SO 4 2− S, occasionally controlled charge neutrality when the NO 3 − N concentration was too low. K + that leached from canopy and from the organic litter influenced the quality of the soil solutions in the young stand down to a depth of 15 cm. Soil organic matter content, and probably the type of organic matter and/or microbiota in each stand were the main factors responsible for differences in the soil solution composition between stands. Although the differences in the soil solution composition were more related to soil characteristics than to stand age, the great differences in the quality of throughfall, stemflow and forest floor solutions were directly related to tree growth and stand characteristics.

NITRIC OXIDE (NO) MODULATES CONTRACTILE RESPONSES OF AIRWAY SMOOTH MUSCLE DURING EARLY POSTNATAL LIFE. † 1995

There are conflicting data on the role of endogenous NO in attenuating airway smooth muscle contraction induced by cholinergic agonists in various adult animal species. We therefore sought to determine whether activation of nitric oxide synthase (NOS) in airway epithelial cells or nerve fibers would modulate tracheal smooth muscle contration induced by acetylcholine (Ach) in young piglets. Tracheal smooth muscle strips were obtained from piglets of two postnatal ages: 3-7 days (n=8) and 2-3 weeks (n=9). After equilibration in an organ bath, tracheal strips were exposed in vitro to increasing concentrations of Ach, before and after blockade of NOS by addition of Nω-Nitro-L-Arginine Methyl Esther (L-NAME) to the bathing medium. Prior administration of L-NAME (18.5 mM) significantly (p<0.5)increased the contractile response to Ach within the first week of life(Fig). A comparable enhancement of Achinduced contraction was observed in response to L-NAME at 2-3 weeks. Removal of epithelium from tracheal strips at both 3-7 and 2-3 wk attenuated the effect of L-NAMEon Ach-induced contraction. We conclude that 1) NO is an important modulator of airway responses to constrictive agents from early in postnatal life, and 2) epithelium is the main source of NO released by exposure to contractile agonists. We speculate that airway epithelial injury in the neonate may remove an important counterbalance to airway constrictor agents.Supp by HL25830 and HL50527

Thin-film gas sensors based on semiconducting metal oxides

In recent years, there has been a gradual realization that an intact environment and properly functioning ecosystems are essential to the continuance of human life; this has led to the tightening up of environmental legislation. As far as air pollution is concerned, gases like sulfur dioxide, the oxides of nitrogen (NO x ), carbon monoxide and carbon dioxide are considered to be the main culprits. Most sulfur dioxide is produced by the combustion of fossil fuels that contain sulfur (coal, oil and natural gas), the sulfur being oxidized to produce sulfur dioxide. This is why SO 2 emissions can only be prevented by chemical binding. Oxides of nitrogen are also produced when fossil fuels are burnt. These oxides are largely the result of reactions between oxygen and nitrogen from the air. The main source of NO x emissions is automobiles. In 1986 alone, more than half (∼ 2 illion tonnes in the former FRG) of all NO x emissions could be directly attributed to this source. In the same year, somewhat less NO x (1 million tonnes in the former FRG) was produced by power stations, distant heating plants and other conversion areas. Air pollution by CO emissions from automobiles is an even more clear-cut case. As CO is produced by the incomplete combustion of fossil fuels, it is not surprising that automobiles alone produced 6.5 million tonnes of this gas in 1986 (former FRG), while the three other user groups (industry/households, trade and business/power stations and distance heating plant, other conversion areas) are only responsible for approximately 2.5 million tonnes (former FRG). The presence of hydrocarbons (CH x ) in exhaust gases is also due to incomplete combustion. Hydrocarbons along with carbon dioxide and water vapour are also considered to be the main causes of the greenhouse effect. With hydrocarbons too, the main source of emissions is the automobile. The emission of CO and CH x from automobiles is particularly abundant when there is an excess of fuel (rich mixture, air coefficient λ<1). The introduction of catalytic converters only provides sufficient recombustion of these components in a very narrow range around λ=1. Therefore, to obtain the most efficient combustion and the least emission of pollutants, it would seem necessary to monitor the combustion process in each cylinder of a vehicle and to control it so that the exhaust gas expelled from each cylinder has a λ value corresponding to the maximum degree of conversion for the catalytic converter. Fast λ measurements are, therefore, of crucial importance, as they make regulation possible during non-stationary phases of engine operations (starting, braking, acceleration) that account for 80% of the total operating time. Attempts are also being made to introduce combustion regulation in incinerators by means of λ coefficients. This type of emission would also require sensors that are capable of continuously monitoring the concentration of pollutant components. Sensor elements based on semiconducting metal oxides seem to be promising both for individual cylinder control in automobiles and for monitoring pollutant components.

Rank dependence of N 2O emission in fluidized-bed combustion of coal

Emissions of N 2O and NO were measured during fluidized-bed combustion of six coals and their chars. The coals ranged in rank from lignite to anthracite. Fractional conversion of coal-bound nitrogen (coal-N) to N 2O was found to increase with coal rank. A similar, although much weaker, trend was observed for NO. For a given coal, the sum of coal-N conversions to N 2O and NO is practically constant over the whole temperature range (1000–1300 K). X-ray photoelectron spectroscopy determination of nitrogen functionality in coals indicates that the percentage of pyridinic-N in coal increases with coal rank, whereas the percentage of pyrrolic-N exhibits the opposite behaviour. The percentage of coal-N retained in the char was determined from elemental analysis and thermogravimetric data. It was found that coal-N retention in char was substantial for all coals and that it increased with coal rank. The contributions to N 2O and NO emissions coming from gas-phase and heterogeneous reactions were evaluated by comparing emissions from coal and char combustion. Results show that although only a relatively small proportion of coal-N is released with the volatiles, gas-phase reactions account for the majority of N 2O emitted from a fluidized-bed combustor. This can be explained by the efficient heterogeneous reduction of N 2O to N 2 which occurs on the char surface immediately after N 2O is formed from char-N. The contribution of char-N to N 2O emission is substantial only for high-rank materials, in the case of which coal-N retention in char is nearly 100%. In contrast to N 2O, char-N was found to be the main source of NO.

Production of nitric oxide in Nitrosomonas europaea by reduction of nitrite

Nitrosomonas europaea and Nitrosovibrio sp. produced NO and N2O during nitrification of ammonium. Less then 15% of the produced NO was due to chemical decomposition of nitrite. Production of NO and especially of N2O increased when the bacteria were incubated under anaerobic conditions at decreasing flow rates of air, or at increasing cell densities. Low concentrations of chlorite (10 μM) inhibited the production of NO and N2, but not of nitrite indicating that NO and N2O were not produced during the oxidative conversion of ammonium to nitrite. NO and N2O were produced during reduction of nitrite with hydrazine as electron donor in almost stoichiometric quantities indicating that reduction of nitrite was the main source of NO and N2O.

Stoicheiometry, kinetics, and mechanism of the oxidation of hyponitrous acid by iodine in acetate buffers

The reaction of hyponitrous acid with iodine occurs as (i) in the pH range 4–6 and at [I–] H2N2O2+ I2+⅙H2O → 2HI +½N2O +⅔NO +⅓HNO3(i) < 0.025 mol dm–3. One of the identified intermediates is HNO2 which is the main source of NO. Several reactions involving HNO2, H2N2O2, and iodide may follow. The decomposition of H2N2O2 is very significant at pH < 4 and [I–] > 0.025 mol dm–3, and the stoicheiometry Δ[H2N2O2]/Δ[I2] changes from 1 :1 to 2:1 or even 6:1. The rate law (ii) applies where Kd′ is the first acid-–d[I2]T/dt=KK′d[H2N2O2]T[I2]T/[H+](1 +K[I–])(ii) dissociation constant of H2N2O2 and K is the equilibrium constant for the formation of I3–; k was found to be (2.1 ± 0.1)× 104 dm3 mol–1s–1at 35 °C employing K′d= 6.3 ×10–8 mol dm–3 and K= 549 dm3 mol–1.

The role of fixed nitrogen in atmospheric photochemistry

Among the N compounds released to the atmosphere, NH 3 and the oxides N 2 O, NO and NO 2 are most important. Various microbial and human activities constitute the main sources of these compounds. NH 3 strongly influences precipitation chemistry, but its role in atmospheric photochemistry is probably not very im portant. The oxides of N, however, must be regarded as key compounds. N 2 O seems to be inert in the troposphere, but its oxidation is the main source of NO in the stratosphere. The more reactive NO and NO 2 act as catalysts in various photochemical reaction chains which affect the residence times of many carbon, sulphur and halogen compounds in the atmosphere through the role that they play in the ozone balance of the atmosphere. The atmospheric abundance of N 2 O , NO, NO 2 and a variety of halogen compounds is increasingly influenced by man. As one of the consequences one may expect changes in the abundance of atmospheric ozone, perhaps leading to increased intensity of ultraviolet radiation at ground level or climatic changes.