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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-671
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
28 Aug 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Evolution of NOx in the Denver Urban Plume during the Front Range Air Pollution and Photochemistry Experiment
Carlena J. Ebben1, Tamara L. Sparks1, Paul J. Wooldridge1, Teresa L. Campos2, Christopher A. Cantrell3, Roy L. Mauldin3, Andrew J. Weinheimer2, and Ronald C. Cohen1,4 1Department of Chemistry, University of California Berkeley, Berkeley, California 94720, USA
2National Center for Atmospheric Research, Boulder, Colorado 80301, USA
3Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado 80309, USA
4Department of Earth and Planetary Sciences, University of California Berkeley, Berkeley, California 94720, USA
Abstract. As NOx (NOx ≡ NO + NO2) is transported away from cities, it undergoes photochemical oxidation to peroxynitrates (RO2NO2, ΣPNs), alkyl nitrates (RONO2, ΣANs), and nitric acid (HNO3). These higher oxide species each have different lifetimes to permanent removal or conversion back to NOx, resulting in nitrogen oxide chemistry that evolves as plumes are transported away from cities. Here, observations from the Front Range Air Pollution and Photochemistry Experiment (FRAPPÉ) are used to describe the evolution of NOx and NOy (NOy ≡ NOx + ΣPNs + ΣANs + HNO3 + …) as the Denver urban plume flows outward from the city center. We evaluate the chemistry, dilution, and deposition rates in the plume to provide numerical constraints on the NOx and NOy,i lifetimes. We find that plume dilution with background air occurs with a lifetime of 3.5 hours. NOx concentrations decrease more rapidly with a lifetime to chemical loss and dilution of 2 hours in the near field of the city center. NOy has an effective lifetime of 3 hours and due to a combination of HNO3 deposition and dilution. The results provide a useful test of conceptual and numerical models of chemistry during the evolution of urban plumes.

Citation: Ebben, C. J., Sparks, T. L., Wooldridge, P. J., Campos, T. L., Cantrell, C. A., Mauldin, R. L., Weinheimer, A. J., and Cohen, R. C.: Evolution of NOx in the Denver Urban Plume during the Front Range Air Pollution and Photochemistry Experiment, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-671, in review, 2017.
Carlena J. Ebben et al.
Carlena J. Ebben et al.
Carlena J. Ebben et al.

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Short summary
We use observations from the FRAPPÉ campaign to examine the evolution of reactive nitrogen as it is transported from Denver. We provide estimates for dilution rates, chemical lifetimes, and deposition rates. While dilution is the primary loss process in the immediate outflow from Denver, chemically, a majority of NOx is converted to HNO3 and is subsequently deposited. Understanding the evolution of reactive nitrogen informs how urban emissions affect air quality in the surrounding regions.
We use observations from the FRAPPÉ campaign to examine the evolution of reactive nitrogen as...
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