The Formation and Growth of Marine Aerosols and the Development of New Techniques for their In-situ Analysis.

Johnson, Graham Richard (2005) The Formation and Growth of Marine Aerosols and the Development of New Techniques for their In-situ Analysis. PhD by Publication, Queensland University of Technology.


Marine aerosols have attracted increasing attention over the past 15 years because of

their potential significance for global climate modelling. The size distribution of these

aerosols extends from super-micrometer sea salt mode particles down through 150 nm

accumulation mode particles, 40 nm Aitken mode particles and nucleation mode

particles which extend from 25 nm right down to clusters of a few molecules. The

process by which the submicrometer modes form and grow and their composition

have remained topics of debate throughout this time in large part because of the

difficulties associated with determining their composition and relating it to proposed

models of the formation process.

The work compared the modality of marine aerosol influencing the South-east-Queensland region with that of other environmental aerosols in the region. The aerosol was found to be consistent with marine aerosols observed elsewhere with

concentrations below 1000 cm-3 and frequently exhibiting the distinct bimodal structure associated with cloud processing, consisting of an Aitken mode at approximately 40 nm, an accumulation mode in the range 100-200 nm and a coarse mode attributed to sea salt between 600 and 1200 nm.

This work included the development of two new techniques for aerosol research. The first technique measures aerosol density using a combination of aerosol size distribution and gravimetric mass concentration measurements. This technique was used to measure the density of a number of submicrometer aerosols including

laboratory generated NaCl aerosol and ambient aerosol. The densities for the laboratory generated aerosols were found to be similar to those for the bulk materials used to produce them. The technique, extended to super-micrometer particle size range may find application in ambient aerosol research where it could be used to discriminate between periods when the aerosol is dominated by NaCl and periods

when the density is more representative of crustal material or sulfates. The technique

may also prove useful in laboratory or industrial settings for investigating particle

density or in case where the composition is known, morphology and porosity.

The second technique developed, integrates the existing physicochemical techniques

of volatilisation and hygroscopic growth analysis to investigate particle composition

in terms of both the volatilisation temperatures of the chemical constituents and their

contribution to particle hygroscopic behaviour. The resulting volatilisation and humidification tandem differential mobility analyser or VH-TDMA, has proven to be a valuable research tool which is being used in ongoing research.

Findings of investigations relating the composition of the submicrometer marine

aerosol modes to candidate models for their formation are presented. Sea salt was not

found in the numerically dominant particle type in coastal nucleation mode or marine

Aitken and accumulation modes examined on the Southeast Queensland coast during

periods where back trajectories indicated marine origin. The work suggests that all

three submicrometer modes contain the same four volatile chemical species and an

insoluble non-volatile residue. The volatility and hygroscopic behaviours of the

particles are consistent with a composition consisting of a core composed of sulfuric

acid, ammonium sulfate and an iodine oxide coated with a volatile organic compound.

The volume fraction of the sulfuric acid like species in the particles shows a strong

dependence on particle size.

Impact and interest:

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ID Code: 16117
Item Type: QUT Thesis (PhD by Publication)
Supervisor: Morawska, Lidia & Ristovski, Zoran
Keywords: Aerosol size distribution, modality, environmental aerosols, marine aerosols, aerosol density, ambient aerosol, VH-TDMA, particle hygroscopic growth, volatility, iodine oxides, non sea salt sulfate, sea salt aerosols, coastal aerosol, marine biota, algae, photolysis, photochemical, thermal decomposition, volatilisation and humidification tandem differential mobility analyser, ultra fine particles.
Divisions: Past > QUT Faculties & Divisions > Faculty of Science and Technology
Past > Schools > School of Physical & Chemical Sciences
Department: Faculty of Science
Institution: Queensland University of Technology
Copyright Owner: Copyright Graham Richard Johnson
Deposited On: 03 Dec 2008 03:56
Last Modified: 22 Feb 2013 02:07

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