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https://doi.org/10.5194/acp-2020-642
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-642
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  07 Jul 2020

07 Jul 2020

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This preprint is currently under review for the journal ACP.

Technical Note: Effect of varying the λ = 185 and 254 nm photon flux ratio on radical generation in oxidation flow reactors

Jake P. Rowe1,a,, Andrew T. Lambe2,, and William H. Brune1 Jake P. Rowe et al.
  • 1Department of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, PA, USA
  • 2Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, MA, USA
  • anow at: Department of Chemistry, University of Colorado, Boulder, CO, USA
  • These authors contributed equally to this work.

Abstract. Oxidation flow reactors (OFRs) complement environmental smog chambers as a portable, low-cost technique for exposing atmospheric compounds to oxidants such as ozone (O3) and hydroxyl (OH) radicals. OH is most commonly generated in OFRs via photolysis of externally added O3 at λ = 254  nm (OFR254), or combined photolysis of O2 and H2O at λ = 185 nm plus photolysis of O3 at λ = 254 nm (OFR185) using low-pressure mercury (Hg) lamps. Whereas OFR254 radical generation is influenced by [O3], [H2O], and photon flux at λ = 254 nm (I254), OFR185 radical generation is influenced by [O2], [H2O], I185, and I254. Because the ratio of photon fluxes, I185 : I254, is OFR-specific, OFR185 performance varies between different systems even when constant H2O and I254 are maintained. Thus, calibrations and models developed for one OFR185 system may not be applicable to another. To investigate these issues, we conducted a series of experiments in which I185 : I254 emitted by Hg lamps installed in an OFR was systematically varied by fusing multiple segments of lamp quartz together that either transmitted or blocked 185 nm radiation. Integrated OH exposure (OHexp) values achieved for each lamp type were obtained using the tracer decay method as a function of UV intensity, humidity, residence time, and external OH reactivity (OHRext). Following previous related studies, a photochemical box model was used to develop a generalized OHexp estimation equation as a function of [H2O], [O3] and OHRext that is applicable for I185 : I254 ≈ 0.001 to 0.1.

Jake P. Rowe et al.

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Short summary
We conducted a series of experiments in which the 185 to 254 nm photon flux ratio (I185 : I254) emitted by low-pressure mercury lamps installed in an oxidation flow reactor (OFR) was systematically varied using multiple novel lamp configurations. Integrated OH exposure values achieved for each lamp type were obtained as a function of OFR operating conditions. A photochemical box model was used to develop a generalized OH exposure estimation equation as a function of [H2O], [O3] and OH reactivity.
We conducted a series of experiments in which the 185 to 254 nm photon flux ratio (I185 : I254)...
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