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@ARTICLE{Ansari:1048492,
      author       = {Ansari, Tabish and Nalam, Aditya and Lupaşcu, Aurelia and
                      Hinz, Carsten and Grasse, Simon and Butler, Tim},
      title        = {{E}xplaining trends and changing seasonal cycles of surface
                      ozone in {N}orth {A}merica and {E}urope over the 2000–2018
                      period: a global modelling study with {NO} x and {VOC}
                      tagging},
      journal      = {Atmospheric chemistry and physics},
      volume       = {25},
      number       = {22},
      issn         = {1680-7316},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2025-04678},
      pages        = {16833 - 16876},
      year         = {2025},
      abstract     = {Surface ozone, with its long enough lifetime, can travel
                      far from its precursor emissions, affecting human health,
                      vegetation, and ecosystems on an intercontinental scale.
                      Recent decades have seen significant shifts in ozone
                      precursor emissions: reductions in North America and Europe,
                      increases in Asia, and a steady global rise in methane.
                      Observations from North America and Europe show declining
                      ozone trends, a flattened seasonal cycle, a shift in peak
                      ozone from summer to spring, and increasing wintertime
                      levels. To explain these changes, we use TOAST 1.0, a novel
                      ozone tagging technique implemented in the global
                      atmospheric model CAM4-Chem which attributes ozone to its
                      precursor emissions fully by $NO_x$ or $VOC+CO+CH_4$ sources
                      and perform multi-decadal model simulations for 2000–2018.
                      Model-simulated maximum daily 8 h ozone (MDA8 $O_3$)
                      agrees well with rural observations from the TOAR-II
                      database. Our analysis reveals that declining local $NO_x$
                      contributions to peak-season ozone (PSO) in North America
                      and Europe are offset by rising contributions from natural
                      $NO_x$ (due to increased $O_3$ production), and foreign
                      anthropogenic- and international shipping $NO_x$ due to
                      increased emissions. Transported ozone dominates during
                      spring. Methane is the largest VOC contributor to PSO, while
                      natural NMVOCs become more important in summer.
                      Contributions from anthropogenic NMVOCs remain smaller than
                      those from anthropogenic $NO_x$. Despite rising global
                      methane levels, its contribution to PSO in North America and
                      Europe has declined due to reductions in local $NO_x$
                      emissions. Our results highlight the evolving drivers of
                      surface ozone and emphasize the need for coordinated global
                      strategies that consider both regional emission trends and
                      long-range pollutant transport.},
      cin          = {JSC},
      ddc          = {550},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {5111 - Domain-Specific Simulation $\&$ Data Life Cycle Labs
                      (SDLs) and Research Groups (POF4-511) / Earth System Data
                      Exploration (ESDE)},
      pid          = {G:(DE-HGF)POF4-5111 / G:(DE-Juel-1)ESDE},
      typ          = {PUB:(DE-HGF)16},
      doi          = {10.5194/acp-25-16833-2025},
      url          = {https://juser.fz-juelich.de/record/1048492},
}