Nitric particle formation

When the flow through the CNC was exhausted outside of the laboratory, we observed particle formation at higher SOp concentrations as expected (Table II). To prove that the radical scavenger effect is reproducible, another radical scavenger (92 ppb nitric oxide) was used in the presence of 110 ppb SOp concentration and 2% humidity, and the supression in particle formation was observed. Another possible mechanism that supressed the particle formation is that more neutralization of polonium ions occurred at the higher humidities and thus ion-induced nucleation would be suppressed. 

The practical motivation for understanding the microscopic details of char reaction stem from questions such as How does the variability in reactivity from particle to particle and with extent of reaction affect overall carbon conversion What is the interdependence of mineral matter evolution and char reactivity, which arises from the catalytic effect of mineral matter on carbon gasification and the effects of carbon surface recession, pitting, and fragmentation on ash distribution How are sulfur capture by alkaline earth additives, nitric oxide formation from organically bound nitrogen, vaporization of mineral constituents, and carbon monoxide oxidation influenced by the localized surface and gas chemistry within pores ... 

This paper deals with the hydrothermal deactivation, under an air + 10 vol. % H2O mixture between 923 and 1173 K, of Cu-MFI solids, catalysts for the selective reduction of NO by propane. Fresh and aged solids were characterized by various techniques and compared with a parent H-ZSM-5 solid. The catalytic activities were measured in the absence and in the presence of water. The differences between fresh and aged Cu-ZSM-5 catalysts (destruction of the framework, extent of dealumination...) were shown to be small in spite of the strong decreases in activity. Cu-ZSM-5 is more resistant to dealumination than the parent H-ZSM-5 zeolite. The rate of NO reduction into N2 increases with the number of isolated Cu VCu ions. These isolated ions partially migrate to inaccessible sites upon hydrothermal treatments. At very high aging temperatures a part of the copper ions agglomerates into CuO particles accessible to CO, but these bulk oxides are inactive. Under catalytic conditions and in the presence of water, dealumination is observed at a lower temperature (873 K) than under the (air + 10 % H2O) mixture, because of nitric acid formation linked to NO2 which is either formed in the pipes of the apparatus or on the catalyst itself... 

Alkaline earth and rare earth metal cocation effects are reported in this paper for copper ion-exchanged ZSM-5 zeolites used for the catalytic decomposition of nitric oxide in 02- free, 02- rich, and wet streams. Severe steaming (20% H2O) of Na-ZSM-5 at temperatures above 6(X)°C leads to partial vitreous glass formation and dealumination. Unpromoted Cu-ZSM-5 catalysts suffer drastic loss of NO decomposition activity in wet gas streams at 500°C. Activity is partially recovered in dry gas. Copper migration out of the zeolite channels leading to CuO formation has been identified by STEM DX. In Ce/Cu-ZSM-5 catalysts the wet gas activity is greatly improved. CuO particle formation is less extensive and the dry gas activity is largely recovered upon removal of the water vapor. 

As soon as I remmed to Mainz, I contacted Dr. Frank Arnold of the Max Planck Institute for Nuclear Physics in Heidelberg to explain my idea about NO removal from the gas phase to him. After about a week he had shown that under stratospheric conditions, solid nitric acid trihydrate (NAT) particles could be formed at temperatures below about 200 K, that is, at temperature about 10 K higher than that needed for water ice particle formation. The paper about our findings was published in Nature at the end of 1986 [69]. Independently, the idea had also been developed by Brian Toon, Rich Turco, and co-workers [70]. Subsequent laboratory investigations, notably by David Hanson and Konrad Mauersberger [71], then of the University of Minnesota, provided accurate information on the thermodynamic properties of NAT. Next it was also shown that the NAT particles could provide efficient surfaces to catalyze the production of ClOx by reactions (23) and (24) [72, 73]. Finally, Molina and Molina [74] proposed a powerful catalytic reaction cycle involving ClO-dimer formation [Eqs. (21), (37), and (38)], which... 

Similarly, SO2 and SO3 (SOJ compounds are produced in combustion by the oxidation of sulfur compounds within the fuel source. SO , emitted into the atmosphere can be incorporated into aerosol particles and wet-deposited as corrosive sulfuric acid. Both NO , and SO , emissions contribute to acid rain content from wet deposition, due to their participation in the formation of nitric and sulfuric acid, respectively. 

Belkner et al. [32] demonstrated that 15-LOX oxidized preferably LDL cholesterol esters. Even in the presence of free linoleic acid, cholesteryl linoleate continued to be a major LOX substrate. It was also found that the depletion of LDL from a-tocopherol has not prevented the LDL oxidation. This is of a special interest in connection with the role of a-tocopherol in LDL oxidation. As the majority of cholesteryl esters is normally buried in the core of a lipoprotein particle and cannot be directly oxidized by LOX, it has been suggested that LDL oxidation might be initiated by a-tocopheryl radical formed during the oxidation of a-tocopherol [33,34]. Correspondingly, it was concluded that the oxidation of LDL by soybean and recombinant human 15-LOXs may occur by two pathways (a) LDL-free fatty acids are oxidized enzymatically with the formation of a-tocopheryl radical, and (b) the a-tocopheryl-mediated oxidation of cholesteryl esters occurs via a nonenzymatic way. Pro and con proofs related to the prooxidant role of a-tocopherol were considered in Chapter 25 in connection with the study of nonenzymatic lipid oxidation and in Chapter 29 dedicated to antioxidants. It should be stressed that comparison of the possible effects of a-tocopherol and nitric oxide on LDL oxidation does not support importance of a-tocopherol prooxidant activity. It should be mentioned that the above data describing the activity of cholesteryl esters in LDL oxidation are in contradiction with some earlier results. Thus in 1988, Sparrow et al. [35] suggested that the 15-LOX-catalyzed oxidation of LDL is accelerated in the presence of phospholipase A2, i.e., the hydrolysis of cholesterol esters is an important step in LDL oxidation. 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

Adsorption of nitric and sulfuric acids on ice particles provides the sol of the nitrating mixture. An important catalyst of aromatic nitration, nitrous acid, is typical for polluted atmospheres. Combustion sources contribute to air pollution via soot and NO emissions. The observed formation of HNO2 results from the reduction of nitrogen oxides in the presence of water by C—O and C—H groups in soot (Ammann et al. 1998). As seen, gas-phase nitration is important ecologically. 

Besides LPS, other particulate and soluble agents are known to stimulate the formation of eicosanoids, e.g. PGE2, PGD2, and thromboxane [57]. These agents also elicit nitric oxide and superoxide anion formation, which may help to destroy phagocytosed microorganisms or particles [58]. 

The conditions under which HC1 formed in acidified sodium chloride droplets would be expected to enter the gas phase have been treated by Clegg and Brimble-combe (1990). Cadle and co-workers (Robbins et al., 1959 Cadle and Robbins, 1960) observed that NaCl aerosols in the presence of 0.1-100 ppm NOz at relative humidities of 50-100% lost chloride ion from the particles. They ascribed this to the formation of nitric acid from NOz, followed by reaction (1). Schroeder and Urone (1974) subsequently suggested that NOz could react directly with NaCl to produce gaseous nitrosyl chloride, C1NO, which they observed using infrared spectroscopy stoichiometrically, this is represented as... 

Other ways of expressing the reactivity of organics in terms of ozone formation and their interrelationships are discussed in detail by Carter (1994), and extension of the principles of this approach to other compounds such as nitric acid, PAN, and aerosol particles is discussed by Bowman and Seinfeld (1994), Bowman et al. (1995), and Derwent et al. (1998). 

Haber [3] investigated the formation of nitric oxide during the combustion of carbon monoxide and came to the conclusion that charged particles— electrons and ions—have an important catalytic effect on the reaction in the flame. 

Orthophosphoric acid is conveniently prepared by boiling one part of red phosphorus with 16 parts of nitric acid—sp. gr. between 1-20 and 1-25—in a bask fitted with a reflux condenser and a ground glass-joint at the neck. Any nitric acid which is volatilized will thus be returned to the flask. Yellow phosphorus is not so quickly attacked by nitric acid as red phosphorus, possibly because the former melts and forms masses which do not present so nearly as large a surface to the action of the acid as do the particles of red phosphorus. The latter, is more expensive. When the phosphorus is all-oxidized, the soln. is evaporated to dryness, and the residue is finally heated in a platinum dish to a temp, not exceeding 180° to make sure that all the nitric acid is driven off. The boiling liquid usually shows the presence of phosphorous acid, which is subsequently oxidized to phosphoric acid. Whether the primary action results in the formation of both acids or of phosphorous acid alone is not clear. If the acid employed for the oxidation be more cone, than that just indicated an explosion may ensue and if a weaker acid be used the action is very slow. 

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