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Title: The Role of Iron-Bearing Minerals in NO 2 to HONO Conversion on Soil Surfaces

Abstract

Nitrous acid (HONO) accumulates in the nocturnal boundary layer where it is an important source of daytime hydroxyl radicals. Although there is clear evidence for the involvement of heterogeneous reactions of NO2 on surfaces as a source of HONO, mechanisms remain poorly understood. We used coated-wall flow tube measurements of NO2 reactivity on environmentally relevant surfaces [Fe (hydr)oxides, clay minerals, and soil from Arizona and the Saharan Desert] and detailed mineralogical characterization of substrates to show that reduction of NO2 by Fe-bearing minerals in soil can be a more important source of HONO than the putative NO2 hydrolysis mechanism. The magnitude of NO2-to-HONO conversion depends on the amount of Fe2+ present in substrates and soil surface acidity. Studies examining the dependence of HONO flux on substrate pH revealed that HONO is formed at soil pH < 5 from the reaction between NO2 and Fe2+(aq) present in thin films of water coating the surface, whereas in the range of pH 5–8 HONO stems from reaction of NO2 with structural iron or surface complexed Fe2+ followed by protonation of nitrite via surface Fe-OH2+ groups. Reduction of NO2 on ubiquitous Fe-bearing minerals in soil may explain HONO accumulation in the nocturnal boundary layermore » and the enhanced [HONO]/[NO2] ratios observed during dust storms in urban areas.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1322503
Report Number(s):
PNNL-SA-117393
Journal ID: ISSN 0013-936X; 48892; 48138; KP1704020
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Science and Technology; Journal Volume: 50; Journal Issue: 16
Country of Publication:
United States
Language:
English
Subject:
Environmental Molecular Sciences Laboratory

Citation Formats

Kebede, Mulu A., Bish, David L., Losovyj, Yaroslav, Engelhard, Mark H., and Raff, Jonathan D. The Role of Iron-Bearing Minerals in NO 2 to HONO Conversion on Soil Surfaces. United States: N. p., 2016. Web. doi:10.1021/acs.est.6b01915.
Kebede, Mulu A., Bish, David L., Losovyj, Yaroslav, Engelhard, Mark H., & Raff, Jonathan D. The Role of Iron-Bearing Minerals in NO 2 to HONO Conversion on Soil Surfaces. United States. doi:10.1021/acs.est.6b01915.
Kebede, Mulu A., Bish, David L., Losovyj, Yaroslav, Engelhard, Mark H., and Raff, Jonathan D. Tue . "The Role of Iron-Bearing Minerals in NO 2 to HONO Conversion on Soil Surfaces". United States. doi:10.1021/acs.est.6b01915.
@article{osti_1322503,
title = {The Role of Iron-Bearing Minerals in NO 2 to HONO Conversion on Soil Surfaces},
author = {Kebede, Mulu A. and Bish, David L. and Losovyj, Yaroslav and Engelhard, Mark H. and Raff, Jonathan D.},
abstractNote = {Nitrous acid (HONO) accumulates in the nocturnal boundary layer where it is an important source of daytime hydroxyl radicals. Although there is clear evidence for the involvement of heterogeneous reactions of NO2 on surfaces as a source of HONO, mechanisms remain poorly understood. We used coated-wall flow tube measurements of NO2 reactivity on environmentally relevant surfaces [Fe (hydr)oxides, clay minerals, and soil from Arizona and the Saharan Desert] and detailed mineralogical characterization of substrates to show that reduction of NO2 by Fe-bearing minerals in soil can be a more important source of HONO than the putative NO2 hydrolysis mechanism. The magnitude of NO2-to-HONO conversion depends on the amount of Fe2+ present in substrates and soil surface acidity. Studies examining the dependence of HONO flux on substrate pH revealed that HONO is formed at soil pH < 5 from the reaction between NO2 and Fe2+(aq) present in thin films of water coating the surface, whereas in the range of pH 5–8 HONO stems from reaction of NO2 with structural iron or surface complexed Fe2+ followed by protonation of nitrite via surface Fe-OH2+ groups. Reduction of NO2 on ubiquitous Fe-bearing minerals in soil may explain HONO accumulation in the nocturnal boundary layer and the enhanced [HONO]/[NO2] ratios observed during dust storms in urban areas.},
doi = {10.1021/acs.est.6b01915},
journal = {Environmental Science and Technology},
number = 16,
volume = 50,
place = {United States},
year = {Tue Aug 16 00:00:00 EDT 2016},
month = {Tue Aug 16 00:00:00 EDT 2016}
}
  • A kinetic study of the nitrous acid decay reaction, 2HONO yields NO + NO/sub 2/ + H/sub 2/O(2), and the formation reaction, NO + NO/sub 2/ + H/sub 2/O yields 2HONO (1), is made using essentially continuous FT-IR monitoring of the reactants and products in mixtures at the ppM level. The data suggest that the reactions are homogeneous for the conditions employed in this study. The results give: k/sub 1/ = (2.2 +- 0.7) x 10/sup -9/ ppM/sup -2/ min/sup -1/ and k/sub 2/ = (1.4 +- 0.4) x 10/sup -3/ ppM/sup -1/ min/sup -1/ at 23/sup 0/C. The homogeneousmore » generation of HONO may be important in power plant plumes and in auto exhaust gases during the early stages of the dilution of these NO/sub x/-H/sub 2/O-rich mixtures. Reactions 1 and 2 are a negligible source and sink of HONO in the atmosphere once the usual low ambient levels of NO and NO/sub 2/ are achieved. These reactions may influence smog formation in urban atmospheres during the early morning hours when nitrous acid formation by aternative pathways is slow. For these conditions the sunlight photolysis of HONO may be the major source of HO-radicals which, in combination with hydrocarbons and their oxidation products, lead to NO yields NO/sub 2/ conversion, O/sub 3/ development, and other manifestations of photochemical smog.« less
  • Well-defined Cu catalysts containing different amounts of zirconia were synthesized by controlled surface reactions (CSRs) and atomic layer deposition methods and studied for the selective conversion of ethanol to ethyl acetate and for methanol synthesis. Selective deposition of ZrO 2 on undercoordinated Cu sites or near Cu nanoparticles via the CSR method was evidenced by UV–vis absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The concentrations of Cu and Cu-ZrO 2 interfacial sites were quantified using a combination of subambient CO Fourier transform infrared spectroscopy and reactive N 2O chemisorption measurements. The oxidation states ofmore » the Cu and ZrO 2 species for these catalysts were determined using X-ray absorption near edge structure measurements, showing that these species were present primarily as Cu 0 and Zr 4+, respectively. Here, it was found that the formation of Cu-ZrO 2 interfacial sites increased the turnover frequency by an order of magnitude in both the conversion of ethanol to ethyl acetate and the synthesis of methanol from CO 2 and H 2.« less
  • Early stage transformations and deposition of iron bearing coal minerals, in particular pyrite (FeS{sub 2}) were studied. An atmospheric lab-scale facility was used to simulate the near burner environments in two different coal conversion processes: (i) Low-NO{sub x} pulverized fuel combustion and (ii) Entrained-flow gasification. Particle sampling showed that for both environments, the pyrite was transformed quickly to pyrrhotite (FeS). In the deposition experiments this pyrrhotite Impacts on the substrates. In the deposition experiments, the chemical composition and the morphology of the slags formed under the two conditions showed clear differences. Special attention was payed to the role of sulphur.more » Based on these (preliminary) experiments, a mechanistic model is proposed for the transformations of pyrite in both pulverized coal conversion systems. Furthermore a description is given of a new experimental setup for future work at elevated pressures (up to 20 bar) to enable a closer simulation of pressurized entrained-flow coal gasification processes.« less
  • The anion-deficient, fluorite-related structures of the manganese-based minerals bixbyite (Mn{sub 2}O{sub 3}), braunite (Mn{sub 7}SiO{sub 12}), braunite II (CaMn{sub 14}SiO{sub 24}) and parwelite (Mn{sub 10}Sb{sub 2}As{sub 2}Si{sub 2}O{sub 24}) are reinterpreted in terms of the coordination defect (CD) theory to gain new insights into their structural interrelationships. CDs are extended, octahedral defects centred by an anion vacancy and including its immediate atomic environment: it is represented as {open_square}M{sub 4}O{sub 6}, where the symbol {open_square} is the anion vacancy. The bixbyite motif is a CD dimer (two edge-sharing octahedra), and this motif repeats, by further edge-sharing, around the 2-fold screw axesmore » of the cubic structure. These same dimers are present in each of the other structures, but the presence of Si{sup 4+} in braunite and braunite II, together with that of other foreign cations such as As{sup 5+} and Sb{sup 5+} in parwelite, leads to different juxtapositions of these motifs. Moreover, the structure of braunite, Mn{sup 2+}(Mn{sup 3+}){sub 6}SiO{sub 12}, reflects the clustering of 12 Mn{sup 3+}-centred octahedra (MnO{sub 6}) around a central SiO{sub 4} tetrahedron to generate a structure for the [(Mn{sup 3+}){sub 6}SiO{sub 12}]{sup 2-} anion which is almost identical to that of the well-known cuboctahedral structure of the PO{sub 4}-centred heteropolytungstate anion, [(W{sup 6+}){sub 12}PO{sub 40}]{sup 3-}. The structure of braunite II, [Ca(Mn{sup 3+}){sub 14}SiO{sub 24}], is simply an intergrowth of slabs of bixbyite- and braunite-type structures, linked by the CaO{sub 8} cubes of the latter. Our various analyses of the reported structure of parwelite in terms of the only possible vacancy assignment have led to some apparent anomalies. We report briefly on these, and have decided to seek confirmation of the reported structure as a consequence. Despite the increasing complexity of these structures, there are clear and defining relationships in the distribution of CDs. The assumption of a close relationship to the fluorite parent in all these structures is based on the observation that the cation sub-lattices are essentially face-centred cubic, with the anions in the tetrahedral sites, so there is little variation from this between one structure and another. The cation contents, however, are very different in the four structures discussed here - a single cation species in bixbyite, two in the braunites and four in parwelite. This factor, and the topology of the CD arrangements, are structure-determining and confirm the close relationships between these four minerals. - Graphical abstract: The anion-deficient, fluorite-related structures of the manganese-based minerals bixbyite (Mn{sub 2}O{sub 3}), braunite (Mn{sub 7}SiO{sub 12}), braunite II (CaMn{sub 14}SiO{sub 24}) and parwelite (Mn{sub 10}Sb{sub 2}As{sub 2}Si{sub 2}O{sub 24}), are reinterpreted in terms of the Coordination Defect (CD) theory to gain new insights into their structural interrelationships. CDs are extended, defects centred by an anion vacancy and including its immediate atomic environment of 4 tetrahedrally coordinated metals and 6 octahedrally coordinated O atoms: it is represented as {open_square}M{sub 4}O{sub 6}, where the symbol {open_square} is the anion vacancy. The arrangement of {open_square}M{sub 4} tetrahedra in bixbyite is shown in the [111] projection.« less
  • This study provides the first in-situ characterization of the products in the heterogeneous reaction 2NO{sub 2}(g) + H{sub 2}O(a) {yields} HONO(g) + HNO{sub 3}(a). Transmission FT-IR spectroscopy and UV-vis spectroscopy were used to probe the heterogeneous chemistry of gas-phase nitrogen dioxide on hydrated SiO{sub 2} particles. At 298 K, gaseous nitrogen dioxide reacts with adsorbed water on the surface of SiO{sub 2} particles to form adsorbed nitric acid and gas-phase nitrous acid. FT-IR spectroscopy of the hydrated SiO{sub 2} surface following reaction with NO{sub 2} provides definitive identification of the adsorbed nitric acid product. The reaction does not occur whenmore » gas-phase nitrogen dioxide is reacted on dehydrated silica particles. The gas-phase product nitrous acid was detected with both FT-IR and UV-vis spectroscopy. Although homogeneous and heterogeneous reactions can contribute to the observed HONO signal, flow cell measurements can be used to distinguish between heterogeneous and homogeneous reaction pathways leading to HONO production.« less