An investigation into the tropospheric chemistry of acidic aerosols and ammonia in the laboratory
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Date
2009
Authors
Townsend, Thomas Michael
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Publisher
University College Cork
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Abstract
This thesis describes a broad range of experiments based on an aerosol flow-tube
system to probe the interactions between atmospherically relevant aerosols with
trace gases. This apparatus was used to obtain simultaneous optical and size
distribution measurements using FTIR and SMPS measurements respectively as
a function of relative humidity and aerosol chemical composition. Heterogeneous
reactions between various ratios of ammonia gas and acidic aerosols were
studied in aerosol form as opposed to bulk solutions. The apparatus is unique, in
that it employed two aerosol generation methods to follow the size evolution of
the aerosol while allowing detailed spectroscopic investigation of its chemical
content. A novel chemiluminescence apparatus was also used to measure [NH4+].
SO2.H2O is an important species as it represents the first intermediate in the
overall atmospheric oxidation process of sulfur dioxide to sulfuric acid. This
complex was produced within gaseous, aqueous and aerosol SO2 systems. The
addition of ammonia, gave mainly hydrogen sulfite tautomers and disulfite ions.
These species were prevalent at high humidities enhancing the aqueous nature of
sulfur (IV) species. Their weak acidity is evident due to the low [NH4+]
produced. An increasing recognition that dicarboxylic acids may contribute
significantly to the total acid burden in polluted urban environments is evident in
the literature. It was observed that speciation within the oxalic, malonic and
succinic systems shifted towards the most ionised form as the relative humidity
was increased due to complete protonisation. The addition of ammonia produced
ammonium dicarboxylate ions. Less reaction for ammonia with the malonic and
succinic species were observed in comparison to the oxalic acid system. This
observation coincides with the decrease in acidity of these organic species. The
interaction between dicarboxylic acids and ‘sulfurous’/sulfuric acid has not been
previously investigated. Therefore the results presented here are original to the
field of tropospheric chemistry. SHO3-; S2O52-; HSO4-; SO42- and H1,3,5C2,3,4O4-;C2,3,4O4
2- were the main components found in the complex inorganic-organic
systems investigated here. The introduction of ammonia produced ammonium
dicarboxylate as well as ammonium disulfite/sulfate ions and increasing the acid
concentrations increased the total amount of [NH4+].
Description
Keywords
Acidic aerosols , Ammonia , Laboratory , Flow-tube
Citation
Townsend, T. M., 2009. An investigation into the tropospheric chemistry of acidic aerosols and ammonia in the laboratory. PhD Thesis, University College Cork.