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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. 2016. "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 = 2016,
month = 8
}
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