Higher measured than modeled ozone production at increased NOx levels in the Colorado Front Range
Bianca Baier1,a,b, William Brune1, David Miller1, Donald Blake2, Russell Long3, Armin Wisthaler4,5, Christopher Cantrell6, Alan Fried7, Brian Heikes8, Steven Brown9,10, Erin McDuffie9,10,11, Frank Flocke12, Eric Apel12, Lisa Kaser12, and Andrew Weinheimer121Department of Meteorology and Atmospheric Science, The Pennsylvania State University, University Park, PA, USA 2School of Physical Sciences, University of California, Irvine, CA, USA 3US EPA National Exposure Research Lab, Research Triangle Park, NC, USA 4Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria 5Department of Chemistry, University of Oslo, Norway 6Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, CO, USA 7INSTAAR, University of Colorado Boulder, Boulder, CO, USA 8Graduate School of Oceanography, The University of Rhode Island, Kingston, RI, USA 9Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA 10Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, CO, USA 11Cooperative Institute for Research in the Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA 12Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO, USA anow at: Cooperative Institute for Research in the Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA bnow at: Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
Received: 03 Dec 2016 – Accepted for review: 22 Dec 2016 – Discussion started: 04 Jan 2017
Abstract. Chemical models must accurately calculate the ozone formation rate, P(O3), to accurately predict ozone levels and test mitigation strategies. However, model chemical mechanisms can contain large uncertainties in P(O3) calculations, which can create uncertainties in ozone forecasts especially during the summertime when P(O3) can be high. One way to test mechanisms is to evaluate model P(O3) using direct measurements. During summer 2014, the Measurement of Ozone Production Sensor (MOPS) measured net P(O3) in Golden, CO, approximately 25 km west of Denver along the Colorado Front Range. Net P(O3) was compared to rates calculated by a photochemical box model using a lumped and a more explicit chemical mechanism. Observed P(O3) was up to a factor of two higher than that modeled during early morning hours when nitric oxide (NO) levels were high, contrary to traditional ozone chemistry theory. This disagreement may be due to model underestimation of hydroperoxyl (HO2) radicals relative to observations at high NO levels. These additional peroxyl radicals could come from the MOPS chamber chemistry or from missing volatile organic compounds co-emitted with NOx; additional cycling of OH into HO2 through reactions involving nitric oxide provides an alternate explanation for higher measured than modeled P(O3). Although the MOPS measurements are new, comparisons of observed and modeled P(O3) in NO space show a similar behavior to other comparisons between P(O3) derived from measurements and modeled P(O3). These comparisons can have implications for the sensitivity of P(O3) to nitrogen oxides and volatile organic compounds during morning hours, and can possibly affect ozone reduction strategies for the region surrounding Golden, CO in addition to other urban and suburban areas that are in non-attainment with national ozone regulations.
Baier, B., Brune, W., Miller, D., Blake, D., Long, R., Wisthaler, A., Cantrell, C., Fried, A., Heikes, B., Brown, S., McDuffie, E., Flocke, F., Apel, E., Kaser, L., and Weinheimer, A.: Higher measured than modeled ozone production at increased NOx levels in the Colorado Front Range, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1089, in review, 2017.