Atmospheric acidity and aerosol nitrate formation

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Ζακούρα, Μαρία
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Atmospheric particles, also known as atmospheric aerosols, are suspended particles (liquid or solid) with diameters ranging from a few nanometers to 100 μm. Atmospheric aerosols affect the Earth’s radiant budget and hence the global climate through their direct and indirect radioactive effects, and also have a negative impact on human health. They can be classified as primary (emitted directly in the particulate phase) or secondary (formed in the atmosphere via chemical reactions involving gas-phase precursors). Atmospheric particles consist of a mixture of inorganic and organic chemical compounds, including nitrate, sulfate, ammonium, organic compounds, elemental carbon, sea salt, soil and water dust, with nitrates being one of the most important inorganic compounds of particles in polluted areas. Acidity is an important atmospheric aerosol property that drives a series of processes related to gas-particle partitioning and heterogeneous chemistry. pH affects the nitrogen cycle through the HNO3/NO3- and NH3/NH4+ gas-particle partitioning. Adverse health outcomes have been linked to strong aerosol acidity by some studies, like respiratory diseases and lung and laryngeal cancers in humans. Chemical transport models are tools well suited for the simulation and detailed study of atmospheric processes. Historically, chemical transport models have had major problems in reproducing the observed aerosol nitrate concentrations in both the US and Europe. Also, it is important that even though aerosol pH affects many processes, the size-dependence of the aerosol pH is not simulated in detail by chemical transport models. This thesis uses the 3-D chemical transport model PMCAMx over US with high grid resolution and in combination with a Plume-in-Grid sub-model to improve the aerosol nitrate predictions. Also, size-resolved aerosol pH predictions over Europe during May 2008 were made for the first time and their variation with time, height, presence of dust is studied, along with their impact on inorganic nitrate.
Aerosols, Nitrate, Acidity