Preprints
https://doi.org/10.5194/acp-2021-584
https://doi.org/10.5194/acp-2021-584

  16 Jul 2021

16 Jul 2021

Review status: a revised version of this preprint is currently under review for the journal ACP.

The influence of weather-driven processes on tropospheric ozone

Tamara Emmerichs1, Bruno Franco2, Catherine Wespes2, Vinod Kumar3, Andrea Pozzer4, Simon Rosanka1, and Domenico Taraborrelli1 Tamara Emmerichs et al.
  • 1Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
  • 2Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
  • 3Satellite Remote Sensing Group, Max Planck Institute for Chemistry, Mainz, Germany
  • 4Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany

Abstract. Near-surface ozone is an harmful air pollutant, which is determined to a considerable extent by weather-controlled processes, and may be significantly impacted by water vapour forming complexes with peroxy radicals. The role of water in the reaction of HO2 radical with nitrogen oxides is known from the literature, and in current models the water complex is considered by assuming a linear dependence on water concentrations. In fact, recent experimental evidence has been published, showing the significant role of water on the kinetics of one of the most important reaction for ozone chemistry, namely NO2 + OH. Here, the available kinetic data for the HOx + NOx reactions have been included in the atmospheric chemistry model ECHAM5/MESSy (EMAC) to test its global significance. Among the modified kinetics, the newly added HNO3 channel from HO2 + NO, dominates, significantly reducing NO2. A major removal process of near-surface ozone is dry deposition accounting for 20 % of the total tropospheric ozone loss mostly occurring over vegetation. However, parameterizations for modelling dry deposition represent a major source of uncertainty for tropospheric ozone simulations. This potentially belongs to the reasons why global models, such as EMAC used here, overestimate ozone with respect to observations. In fact, the employed parameterization is hardly sensitive to local meteorological conditions (e.g., humidity) and lacks non-stomatal deposition. In this study, a dry deposition scheme including these features have been used in EMAC, affecting not only the deposition of ozone but of its precursors, resulting in lower chemical production of ozone. Additionally, we improved the emissions of isoprene and nitrous acid (HONO). Namely, for isoprene emissions we have accounted for the impact of drought stress which confers a higher model sensitivity to meteorology leading to reduced annual emissions down to 32 %. For HONO, we have implemented soil emissions, which depend on soil moisture and thus on precipitation. We estimate for the first time a global source strength of 7 Tg(N) a−1. Furthermore, the usage of a parameterization for the production of lightning NOx that depends on cloud top height contributes to a more realistic representation of NO2 columns over remote oceans with respect to the satellite measurements of the Ozone Monitoring Instrument (OMI). The combination of all the model modifications reduces the simulated global ozone burden by ≈ 20 % to 337 Tg, which is in better agreement with recent estimates. By comparing simulation results with measurements from the Infrared Atmospheric Sounding Interferometer (IASI) and the Tropospheric Ozone Assessment Report (TOAR) databases (of 2009) we demonstrate an overall reduction of the ozone bias by a factor of 2.

Tamara Emmerichs et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-584', Anonymous Referee #1, 22 Jul 2021
  • RC2: 'Comment on acp-2021-584', Anonymous Referee #2, 12 Sep 2021

Tamara Emmerichs et al.

Tamara Emmerichs et al.

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Short summary
Near-surface ozone is a harmful air pollutant and it is strongly affected by radical reactions and surface-atmosphere exchanges which in turn are modulated, directly and indirectly, by weather. Understanding the impact of weather on ozone, and air quality, is thus important also in view of weather extremes. The inclusion of additional ozone-weather links in the global model yields a 2-fold reduction of the ozone bias towards satellite observations.
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