Showing papers on "NOx published in 1988"

Photochemistry of biogenic emissions over the Amazon forest

Abstract: The boundary layer chemistry over the Amazon forest during the dry season is simulated with a photochemical model. Results are in good agreement with measurements of isoprene, NO, ozone, and organic acids. Photochemical reactions of biogenic isoprene and NOx can supply most of the ozone observed in the boundary layer. Production of ozone is very sensitive to the availability of NOx, but is insensitive to the isoprene source strength. High concentrations of total odd nitrogen (NOy) are predicted for the planetary boundary layer, about 1 ppb in the mixed layer and 0.75 ppb in the convective cloud layer. Most of the odd nitrogen is present as PAN-type species, which are removed by dry deposition to the forest. The observed daytime variations of isoprene are explained by a strong dependence of the isoprene emission flux on sun angle. Nighttime losses of isoprene exceed rates of reaction with NO3 and O3 and appear to reflect dry-deposition processes. The 24-hour averaged isoprene emission flux is calculated to be 38 mg/sq m per day. Photooxidation of isoprene could account for a large fraction of the CO enrichment observed in the boundary layer under unpolluted conditions and could constitute an important atmospheric source of formic acid, methacrylic acid, and pyruvic acid.

On the nonlinearity of the tropospheric ozone production

Abstract: The relationship of photochemical ozone production versus photochemical loss of an ozone precursor, that is, either NOx or nonmethane hydrocarbons (NMHCs), is studied by using a box model with particular emphasis on the nonlinearity problem of the relationship with respect to the concentration of the precursor. Model calculations indicate that the composition of NMHCs, the ratio of NMHCs to NOx, and the background concentrations of natural hydrocarbons, CO, and CH4 all play important roles in determining the nonlinearity of O3 production with respect to the loss of NOx. In addition, influences on the nonlinearity due to radical loss via reactions of HO2 with RO2, exchanges between PAN and NO2, and inclusion of nighttime NOx loss processes are also investigated. Mechanisms that contribute to the nonlinearity are discussed. The nonlinear property of O3 production versus loss of hydrocarbons and CO is different from that of NOx. When the sum of CO and all hydrocarbons, including CH4, natural NMHCs, and anthropogenic NMHCs, is used as the reference O3 precursor, the nonlinearity is much less pronounced for ambient conditions usually found in rural air.

Diesel fuel derived from vegetable oils, III. Emission tests using methyl esters of used frying oil

Abstract: The preparation of methyl esters of used frying oil, available as waste from restaurants and households, is described. Fuel specifications of this fuel are given, and values for gaseous (HC, CO, NOx) and particulate emissions, measured with a vehicle powered by a turbocharged, direct injection diesel engine, are shown. The ester fuel shows slightly lower HC and CO emissions but increased NOx values compared with reference US-2D fuel. The particulate emissions, however, are significantly lower with used frying oil. Preliminary results of an engine road test are described.

Evidence for ≥C 3 alkyl nitrates in rural and remote atmospheres

Abstract: Interactions of odd-nitrogen compounds with non-methane hydro-carbons and a variety of radical species have been shown to have a potential impact on atmospheric chemistry on local, regional, and even global scales1–9. To understand the interactions of atmospheric nitrogen compounds requires an accurate budget of individual reactive nitrogen species. But recent attempts to obtain a mass balance between total reactive nitrogen (NOy) and individual reactive nitrogen species (NO-I-NO2+HNO3+PAN (peroxyacetyl nitrate) +PPN (peroxypropionyl nitrate) + particulate NO−3) have not accounted for all NO9,10y. One class of compound proposed to account for some of the NOy deficit is the alkyl nitrates (RONO2)5,10–12, although ambient measurements have not been available to test this hypothesis. Here I report measurements of RONO2 made in the North Pacific atmosphere, providing the first direct evidence for existence and transport of ≥C3 alkyl nitrates in the troposphere. I also observed a variation in alkyl nitrate concentration which suggests these compounds may be used as unique tracers of 'polluted' air masses to remote areas. These observations are significant because relatively long-lived alkyl nitrates can serve as reservoirs of reactive nitrogen in the remote troposphere, where they can be converted to NOx, a key catalyst in ozone formation and destruction3,4.

Scenarios of possible changes in atmospheric temperatures and ozone concentrations due to man's activities, estimated with a one-dimensional coupled photochemical climate model

Abstract: A one-dimensional coupled climate and chemistry model has been developed to estimate past and possible future changes in atmospheric temperatures and chemical composition due to human activities. The model takes into account heat flux into the oceans and uses a new tropospheric temperature lapse rate formulation. As found in other studies, we estimate that the combined “greenhouse effect” of CH4, O3, CF2Cl2, CFCl3 and N2O in the future will be about as large as that of CO2. Our model calculates an increase in average global surface temperatures by about 0.6°C since the start of the industrial era and predicts for A.D. 2050 a twice as large additional rise. Substantial depletions of ozone in the upper stratosphere by between 25% and 55% are calculated, depending on scenario. Accompanying temperature changes are between 15°C and 25°C. Bromine compounds are found to be important, if no rigid international regulations on CFC emissions are effective. Our model may, however, concivably underestimate possible effects of CFCl3, CF2Cl2, C2F3Cl3 and other CFC and organic bromine emissions on lower stratospheric ozone, because it can not simulate the rapid breakdown of ozone which is now being observed worldwide. An uncertainty study regarding the photochemistry of stratospheric ozone, especially in the region below about 25 km, is included. We propose a reaction, involving excited molecular oxygen formation from ozone photolysis, as a possible solution to the problem of ozone concentrations calculated to be too low above 45 km. We also estimate that tropospheric ozone concentrations have grown strongly in the northern hemisphere since pre-industrial times and that further large increases may take place, especially if global emissions of NOx from fossil fuel and biomass burning were to continue to increase. Growing NOx emissions from aircraft may play an important role in ozone concentrations in the upper troposphere and low stratosphere.

Tropospheric ozone : regional and global scale interactions

Abstract: I Presentations.- Tropospheric Ozone: An Overview.- Transport of Pollutants on Different Scales in the Troposhere.- Ozone on an Urban and Regional Scale-With Special Reference to the Situation in the Netherlands.- Ozone Measurements in Historic Perspective.- Large Scale Distributions of O3, CO and CH4 in the Troposphere from Scientific Aircraft Measurements (Stratoz III).- Ozone Changes at the Surface and in the Free Troposphere.- Tropospheric Ozone Lidar Measurements.- Tropospheric Ozone from Satellite Total Ozone Measurements.- Stratosphere-Troposphere Exchange of Ozone.- Measurements of Ozone at Two Background Stations in Finland.- Ozone-Climate Interactions Associated with Increasing Atmospheric Trace Gases.- Ozone Effects on Vegetation.- The Measurement of NOx in the Non-Urban Troposphere.- NOx Sources and the Tropospheric Distribution of NOx during Stratoz III.- Calculation of the Distribution of NOx Compounds in Europe.- Atmospheric Chemistry of NOx and Hydrocarbons Influencing Tropospheric Ozone.- Ozone Production in the Black Forest: Direct Measurements of RO2, NOx and Other Relevant Parameters.- Model Studies of Background Ozone Formation.- Global Transport of Ozone.- The Ozone Problem in Rural Areas of the United States.- A Program of Tropospheric Ozone Research (TOR).- The Aeroce Project.- Sampling Mid-Tropospheric Air at Aeroce Surface Sites.- II Working Group Summaries.- Atmospheric Transport.- NOx in the Troposphere.- The Regional Ozone Problem.- Backgroud Ozone.

The Measurement of NOx in the Non-Urban Troposphere

Abstract: The measurements of NOx that have been made in the non-urban troposphere are reviewed. The NOx levels in the clean remote troposphere are very low: 0.01 ppbv at the surface in the Mid-Pacific, but increasing with altitude to approximately 0.2 ppbv in the upper troposphere. The upper tropospheric NOx levels are maintained by lightning, stratospheric injection, high flying aircraft and convective transport of surface pollution. Surface NOx mixing ratios over large regions of the industrial Northern Hemisphere exceed 1 ppbv. At the surface in more isolated continental areas the NOx mixing ratio will be intermediate between those found in industrial regions and remote maritime locations. The NOx mixing ratio in the clean troposphere may be strongly influenced by other reactive nitrogen oxides such as PAN. PAN and PAN-like compounds may be the dominate reactive nitrogen oxide species in many regions of the troposphere. This complicates the estimation of the tropospheric NOx distribution and presents substantial difficulties in the measurement of tropospheric NOx levels.

Process for removal of nox from fluid streams

Abstract: There is provided a process and apparatus for carrying out the process, to remove nitrogen oxides from a gas stream. The process is characterized by passing the gas stream through a first catalytic zone in the absence of added ammonia and in the presence of an oxidation catalyst to convert the NO content thereof to NO 2 , thereafter introducing ammonia into the gas stream, and catalytically reducing the NO 2 to nitrogen and water in the presence of a catalyst. Higher conversion to innocuous materials is obtained.

Lean Low NOx Primary Zones Using Radial Swirlers

Abstract: Swirling flow primary zones with between 30% and 60% simulated primary zone air flow were investigated using curved blade radial swirlers. Two radial swirlers were compared with the same open area but different outlet diameters, d, giving different expansion ratios, D/d, from the swirler to the combustor diameter, D. Two combustors were used, 76 mm and 140 mm diameter, the larger one corresponding to the size of several gas turbine can combustors. There was no influence of D/d on the weak extinction. It was demonstrated that an adequate efficiency was not achieved in the weak region until there was a significant outer expansion and associated recirculation zone. It was shown that these systems with central gaseous fuel injection had good flame stability with very low NOx emissions. Propane and natural gas were compared and the NOx emissions were 50% lower with natural gas. The optimum NOx emissions, compatible with a high combustion efficiency, were close to 10 ppm NOx emissions corrected to 15% oxygen.Copyright © 1988 by ASME

Process and device for purifying off-gas or waste gas

Abstract: A sorption bed, arranged as a moving-bed reactor with or without circulating fluidised layers or as a fixed-bed reactor, is used for dry decontamination of waste gas or exhaust air by passing, in the temperature range between 30 and 130@C, acidic and/or oxidisable toxic gases contained in a waste gas having an oxygen content of at least 2% through sorbents introduced in the dry state. The toxic gases can be SOx, HCl, HF, NOx CO and hydrocarbons. The mean residence time of the sorbents is at least 20 minutes, generally several hours or days, and the mean particle size is at most 125 mu m. Fresh sorbent is supplied in an approximately stoichiometric amount, and used sorbent is removed correspondingly. The sorbents used are chiefly cooking soda and Ca(OH)2 or Mg(OH)2. Chlorides, fluorides, sulphate-sulphite mixtures and nitrate-nitrite mixtures, and mixtures of all the compounds mentioned occur in used sorbents. In particular, the carbonated reaction product from the low temperature range is reactivated by being returned to the combustion chamber of the combustion process, so that it can be used in a preliminary stage chiefly for desulphuration, dechlorination or defluorination. On account of its low temperature characteristics, the process can also be used for purification of exhaust air, in particular tunnel exhaust air, carbon monoxide and hydrocarbon being oxidised. The used sorbent is thus carbonated, so that in this case it is completely reusable for high-temperature decontamination of combustion chamber gases in a combustion chamber.

Reaction of Nitrogen Oxides with Black Carbon: An FT-IR Study

Abstract: Qualitative and quantitative studies of the reaction of black carbon with the oxides of nitrogen, including NO, NO2/N2O4, N2O, and N2O3, have been carried out with the use of Fourier transform infrared spectroscopy (FT-IR). The active reactant is shown to be NO2, whether it acts as a disproportionation product or as an impurity in the gas under study. FT-IR spectra of the surface species identify them as resulting from reaction of carbon with NO2. For paraffin candle soot which was exposed simultaneously to oxygen atoms, and nitric oxide at 298 K, the surface species also are due to NO2, formed by oxidative adsorption of NO on the soot surface.

Low NOx high efficiency combustion process

Abstract: A process to combust fuel and oxidant at high efficiency and with low NOx generation even when the fuel has non-uniform characteristics and the oxidant is pure oxygen, wherein fuel and oxidant are first combusted within a high velocity oxidant-rich jet, fuel is mixed with combustion products in a recirculation zone and the mixture is aspirated into the oxidant-rich jet and combusted in a diffuse secondary flame at the periphery of the oxidant-rich jet.

Exhaust gas purifying catalyst and process for producing the same

Abstract: An exhaust gas purifying catalyst for oxidizing HC and CO and for reducing NOx is provided, which comprises at least one oxide of rare earth element, rhodium, and at least one of platinum and palladium loaded on alumina grains The major amount of rhodium is dispersed on the oxide of rare earth element Thus, the rhodium solidification into the alumina grains is prevented Further, when cerium oxide accompanying lanthanum oxide, neodymium oxide or a mixture thereof is used as the oxide of rare earth element, the sintering of cerium oxide or palladium at a high temperature is suppressed since it forms a complex oxide with lanthanum oxide, neodymium oxide or a mixture thereof Additionally, when stabilized alumina grains in which a rare earth element and an alkali earth element are present in a solid solution state are used, the deterioration of NOx purifying activity of the catalyst at a high temperature is suppressed The exhaust gas purifying catalyst of this invention has high durability as well as high activity at a high temperature

Ozone Production in the Black Forest: Direct Measurements of RO2, NOx and Other Relevant Parameters

Abstract: The in-situ production of ozone was investigated from simultaneous measurements of RO2-radicals, O3, NOx, and the NO2-photo-lysis frequency during a field campaign in the Black Forest, FRG, in July 1986. During one day, the measured RO2 concentrations agree well with those calculated from the photostationary state of NOx. On the second day, extremely high RO2 concentrations were observed which are not reflected in a corresponding O3 production. It is concluded that some RO2 radicals have a significantly reduced reactivity with respect to NO than is commonly believed. Also, the measured ratio of HO2 to organic peroxy radicals was much lower than that derived from accepted chemical decomposition schemes of hydrocarbons.

Low NOx regenerative burner

Abstract: A regenerative burner having heat storage units with combustion effluent/combustion air ducts therethrough, fuel intake means and a burner body, wherein the burner is designed to suppress NOx formation and to control flame shape and characteristic in the regenerative system during combustion. The regenerative burner may include a burner baffle, or may include a plurality of gas jets entrained in generally converging fashion for control of the flame characteristics and shape dispositive of NOx formation. The burner may provide for staged combustion, either by means of sequential fuel injection or sequential provision of combustion air, or the burner may depress NOx formation by vitiation of combustion air with products of combustion. The present regenerative burners suppress NOx formation yet preserve the remaining characteristic features of regenerative systems.

An advanced selective reduction process for NOx control

Abstract: The combustion of coal and heavy oil produces significant quantities of NOx (NO + NO2), which ultimately participates in photochemical smog and acid rain. Combustion modification schemes, such as staged combustion1 and reburning2, or downstream injection of selective reducing agents, particularlarly ammonia3 and urea4, can significantly reduce NOx emissions, but their effectiveness may be limited by operating constraints. Perry and Siebers5 described a selective reduction process using cyanuric acid, reported to be effective over a broad temperature range. Here we report new data that indicate that the same reductions can be achieved without stainless steel to activate the reaction mechanism, if the process is combined with reburning or staged combustion (or slightly fuel-rich operation in internal combustion) to produce carefully controlled stoichiometry. The NOx reductions that can be achieved with cyanuric acid and other –NH- and –CN-containing compounds at relatively low temperatures exceed those possible with either combustion modifications or selective reduction techniques alone or in normal combination.

Catalysis in Combustion

Abstract: Catalysis and combustion have long been linked. In fact, the science of catalysis stems from Davy's discovery [1] that platinum wires could promote the flameless combustion of flammable fuel-air mixtures. Today, catalysis is a mainstay of our modern chemical industry. Oxidation catalysts are used not only for the complete oxidation of fuels to carbon dioxide and water, as in radiant catalytic tent heaters and fume abatement devices, but also for the selective partial oxidation of hydrocarbons or other “fuels” to produce basic chemicals such as ethylene oxide (from ethylene), terephthalic acid (from p-xylene), and nitric acid (from ammonia). However, despite the long-known capability of catalysts to oxidize hydrocarbons without significant production of carbon monoxide, soot, or thermal NOx, there seemed little possibility that catalytic oxidation reactors could ever displace conventional flame combustors as primary fuel combustors. This is because the volumetric heat release rates of conventional...

UNSTEADY-STATE PERFORMANCE OF NO x CATALYTIC REDUCTION BY NH 3

Abstract: Experimental results of studying NOx catalytic reduction by NH3 under periodic reversals in the direction of filtration of the mixture purified in a catalyst bed are discussed.

Oxides of nitrogen detector

Abstract: A structure and method for sensing oxides of nitrogen in a gas. The gas is first passed through an oxidation catalyst and any reducing species in the gas are oxidized. The output gas from the oxidation catalyst is received by a sensor which generates an output responsive to oxides of nitrogen because the sensor has been isolated from any reducing species in the gas.

Mass transfer in the absorption of nitrogen oxides in alkaline solutions

Abstract: The absorption of mixtures of nitrogen oxides into aqueous solutions of NaOH in the range of partial pressures of 0.004- to 0.05-atm NO and 0.002- to 0.015-atm NO2 was investigated. Absorption experiments were conducted in a gas-liquid contactor that permitted independent variation of the gas and liquid mass transfer coefficients. The results were analyzed in terms of a model which accounted for diffusion, reaction, and formation of higher oxides and oxyacids in the gas and in the liquid phases. Absorption of both HNO2 and N2O3, formed in the bulk gas and within the gas diffusion film, were found to be significant. Using a rate coefficient of 8.8 × 10−3 mol/s · cm3 · atm3 for the formation of HNO2 in the gas phase (England and Corcoran, 1975), a value of the absorption factor, H √Dk, for N2O3 of 2.5 × 10−3 mol/s cm2 atm was determined at 25°C. This value was found to decrease with temperature and was 1.2 × 10−3 at 40°C. The use of concentrated base as an absorbent solution prevented the formation of nitric acid mist, a problem encountered in many previous studies of NOx absorption.

Method of treating waste gas by irradiation with electron beam

Abstract: A waste gas containing sulfur oxides (SOx) and/or nitrogen oxides (NOx) is purified by leading the waste gas to a radiation irradiation zone, adding ammonia (NH3) to the waste gas before, during or after the irradiation, collecting the resulting by-product (ammonium sulfate and/or ammonium nitrate) by means of a dust collector, and releasing the purified waste gas to the atmosphere. The amount of NH3 to be added is selected so as to be smaller than an amount calculated from target desulfurization and denitrification efficiencies so that it is possible to reduce the leakage of ammonia despite variations in the composition of the waste gas. Further, an alkaline substance exclusive of ammonia is added to the waste gas within the dust collector or at the upstream side thereof so that the pH of the collected by-product is adjusted to 6 or more, preferably 7 or more, thereby suppressing the adverse effects of sulfamic acid impurities.