Iron Oxides as Key Catalysts in the Conversion of Nitrogen Dioxide to Nitrous Acid on Atmospheric Boundary Layer Surfaces
EMSL Project ID
48138
Abstract
Photolysis of HONO is the primary source of hydroxyl radical, which reacts with volatile organic compounds and nitrogen oxides (NOx) to generate the ozone and aerosols associated with photochemical air pollution. Despite its importance, atmospheric chemistry models consistently under-predict the atmospheric concentration of HONO levels. The central hypothesis of the proposed work is that redox-active transition metals such as iron, which are abundant components of boundary layer surfaces (e.g., soil and urban infrastructure), serve as active sites that catalyze NO2-to-HONO conversion. We have formulated this hypothesis based on preliminary findings which shown that NO2 is efficiently converted into HONO on soil collected from an agricultural region in central Indiana. The objectives of this study are (1) to measure the NO2-to-HONO conversion efficiency as a function of initial NO2 concentration and relative humidity on on iron oxide surfaces, which are surrogates for mineral components found in soil, rust, and suspended dust particles, and (2) to probe the mechanism of HONO formation from reactions on iron oxide surfaces. We have successfully achieved Aim 1, and urgently need the expertise offered by EMSL to complete Aim 2 before publication of this work and to obtain preliminary results for competitive proposals for future funding. Specifically, we are proposing X-ray photoelectron spectroscopy (XPS) experiments to provide evidence that Fe redox chemistry is responsible for NO2-to-HONO conversion. The proposed research fits two of EMSL’s current Science Themes: Science of Interfacial Phenomena and Geochemistry/Biogeochemistry. In addition, the work is compatible with the mission of the Office of Biological and Environmental Research since the results will help us understand how iron in soil mediates the atmospheric-terrestrial exchange of reactive gases such as NOx and HONO. This is part of our long-range goal to quantitatively evaluate the relative importance of biogenic vs. abiotic conversion of nitrate and ammonium in soil into reactive nitrogen species that impact air quality. The work is critical for improving our understanding of fundamental air pollution mechanisms and for improving the predictive models used to inform effective air quality and climate policy. The surface-sensitive techniques and expertise at EMSL are not commonly available at other institutions. It is very likely that incorporating surface methods in our research will provide unique insights into the dynamics of nitrogen and iron species in boundary layer surfaces that would not be possible with other techniques or at our home institution.
Project Details
Project type
Limited Scope
Start Date
2013-11-20
End Date
2014-01-07
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Kebede M A,Bish D L,Lozovyi Y ,Engelhard M H,Raff J D 2016. "The Role of Iron-Bearing Minerals in NO2 to HONO Conversion on Soil Surfaces" Environmental Science & Technology 50(16):8649–8660. 10.1021/acs.est.6b01915