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@PHDTHESIS{Milousis:1042327,
      author       = {Milousis, Alexandros},
      title        = {{A}dvances in {U}nderstanding {N}itrate {A}erosol
                      {F}ormation and the {I}mplications for {A}tmospheric
                      {R}adiative {B}alance},
      volume       = {663},
      school       = {Köln},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2025-02530},
      isbn         = {978-3-95806-823-0},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {195},
      year         = {2025},
      note         = {Dissertation, Köln, 2025},
      abstract     = {Recent decades have highlighted the profound consequences
                      of air pollution on air quality and human health, resulting
                      in millions of deaths worldwide and contributing to the
                      intensification of the Earth’s climate due to ongoing
                      anthropogenic emissions. These emissions, originating from
                      densely populated and industrialized regions, lead to the
                      release of gaseous pollutants that undergo chemical
                      transformations in the atmosphere, producing secondary
                      particulate pollutants. Atmospheric modeling is a valuable
                      tool that facilitates a more profound comprehension of
                      physicochemical processes, thereby providing guidelines for
                      mitigating air pollution and enhancing our understanding of
                      climatic feedback mechanisms. Recent policies aimed at
                      reducing emissions from anthropogenic activities have
                      predominantly focused on specific species, including carbon
                      dioxide (CO2), methane (CH4), sulfur dioxide (SO2), and
                      nitrogen oxides (NOx). This is expected to cause a change in
                      the landscape of secondary aerosol population
                      characteristics as the abundancy of their precursors will
                      also change. For example, the observed historical increase
                      in ammonia (NH3) emissions is expected to enhance the
                      importance of certain inorganic aerosol species at the
                      expense of others. A substantial body of research conducted
                      in the most heavily polluted regions of the Northern
                      Hemisphere has already demonstrated that the average
                      concentration of aerosol nitrate is comparable to, if not
                      greater than, the respective concentration of aerosol
                      sulfate. Sulfate is currently recognized as the most
                      substantial contributor to the total inorganic aerosol mass
                      on a global scale. Consequently, the estimation of aerosol
                      nitrate by atmospheric models has become increasingly
                      crucial, and the number of models that include this species
                      in their calculations is steadily rising, despite not being
                      the norm in the past. This thesis aims to address a key
                      assumption that can influence the estimation of nitrate
                      aerosols (NO3 -) by models. This assumption is their
                      physical state (i.e., solid or liquid). Aerosols typically
                      crystallize and form solids when exposed to decreasing
                      ambient relative humidity, though this process is often
                      complex due to various aerosol compositions and the
                      hysteresis effect .In thermodynamics, particles that form
                      solids are considered to be in a stable state; however,
                      aerosol water can exist even in very low humidity values,
                      leaving particles in a supersaturated aqueous state called
                      metastable. Utilizing a state-of-the-art chemistry and
                      climate model (EMAC) and a recently developed version of a
                      thermodynamic equilibrium model (ISORROPIA-lite), the study
                      explores the hypothesis that the state assumption
                      significantly impacts inorganic aerosol estimations.
                      Additionally, it examines the impact of the aerosol physical
                      state on the estimated particle acidity, as this is another
                      quantity that influences the aerosol partitioning process.
                      Furthermore, the thesis investigates a number of factors
                      that are known to influence the model’s ability to
                      accurately estimate NO3 - concentrations in regions of high
                      anthropogenic activity, with a particular focus on the
                      polluted North Hemisphere (East Asia, India, Europe, and
                      North America). The objective is to ascertain the most
                      significant factors that contribute to the best replication
                      of observations of NO3 - in sizes less than 1 μm and 2.5
                      μm in diameter (PM1 and PM2.5, respectively). The analysis
                      is further expanded to encompass the recognition of any
                      seasonal patterns as well as measurement location patterns.
                      Finally, the study examines the interactions between nitrate
                      aerosol and mineral dust, thereby investigating the climatic
                      impact of NO3 - with respect to its radiative effect from
                      both aerosol-radiation interactions (direct effect) and
                      aerosol-cloud interactions (indirect effect).The importance
                      of considering dustnitrate interactions when examining such
                      metrics is also quantified. The study found that the
                      physical state assumption has a minimal impact on the global
                      budget of key inorganic aerosol species, including NO3 -,
                      SO4 2-, and NH4 +, as well as non-volatile cations, with
                      overall differences being less than $10\%.$ Consequently,
                      for the purposes of climatic or air quality simulations that
                      cover a long time period and consider a global scale, that
                      choice is not expected to have a significant impact.
                      However, the metastable assumption has been shown to yield
                      faster simulation times, with an average increase of
                      approximately $4-5\%.In$ regions characterized by
                      consistently low relative humidity values and/or mid-range
                      temperatures, the assumption of considering only liquid
                      particles has been found to result in lower concentration
                      estimates, with NO3 - concentrations being reduced by up to
                      $40\%,$ and slightly more acidic particles by up to 1 unit.
                      Consequently, for analyses that consider specific regions,
                      the aerosol physical state assumption assumes greater
                      importance. Concerning the factors influencing the accuracy
                      of NO3 - estimations, it was ascertained that, on average, a
                      high model grid resolution and a low dinitrogen pentoxide
                      (N2O5) hydrolysis coefficient tend to yield better agreement
                      with observations in both sizes. The employment of disparate
                      anthropogenic emissions databases emerged as a significant
                      factor influencing model estimations, particularly in
                      replicating PM1 NO3 - concentrations across diverse regions.
                      In general, there is no ’perfect’ model setup capable of
                      best capturing both PM1 and PM2.5 NO3 - concentrations
                      across all regions simultaneously. Depending on the area of
                      interest, different parameterizations yield superior rates
                      of agreement. Furthermore, it was determined that nitrate
                      aerosols induce a net cooling direct radiative effect of
                      -0.11 W/m2, primarily attributable to the scattering of SW
                      radiation by smaller size modes, accounting for $85\%$ of
                      this estimate. Conversely, nitrate aerosols have been
                      observed to induce a net warming indirect radiative effect
                      of +0.17 W/m2, which is attributed to the depletion of
                      smallersized particles (i.e., anthropogenic pollution)
                      through coagulation with larger particles (i.e., dust). This
                      depletion results in the formation of less low-level warm
                      clouds, which decreases the amount of SW radiation that is
                      reflected back to space. The efficacy of this mechanism is
                      further augmented by nitrate-dust interactions, which
                      augment the size of dust particles through adsorption and
                      coating processes. The incorporation of dust chemistry is of
                      paramount importance when compared to assumptions for dust
                      composition or dust loading, as its omission engenders an
                      underestimation of the aforementioned estimates by up to
                      $45\%.$},
      cin          = {ICE-3},
      cid          = {I:(DE-Juel1)ICE-3-20101013},
      pnm          = {2111 - Air Quality (POF4-211)},
      pid          = {G:(DE-HGF)POF4-2111},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:0001-2507140935090.986494451029},
      doi          = {10.34734/FZJ-2025-02530},
      url          = {https://juser.fz-juelich.de/record/1042327},
}