Characterisation of episodic aerosol types over the Australian continent Y. Qin and R. M. Mitchell CSIRO Marine and Atmospheric Research, Centre for Australian Weather and Climate Research, a partnership between CSIRO and the Australian Bureau of Meteorology, Canberra, ACT, Australia
Abstract. Classification of Australian continental aerosol types resulting from episodes of
enhanced source activity, such as smoke plumes and dust outbreaks, is carried out
via cluster analysis of optical properties obtained from inversion of sky
radiance distributions at Australian aerosol ground stations using data obtained
over the last decade. The cluster analysis distinguishes four significant classes,
which are identified on the basis of their optical properties and provenance as
determined by satellite imagery and back-trajectory analysis. The four classes are
identified respectively as aged smoke, fresh smoke, coarse dust and a
While the first three classes show similarities with comparable
aerosol types identified elsewhere, the super-absorptive aerosol has no obvious
foreign prototype. The class identified as coarse
dust shows a prominent depression in single scattering albedo in the blue spectral
region due to absorption by hematite, which is shown to be more abundant in
central Australian dust relative to the "dust belt"of the Northern Hemisphere.
The super-absorptive class is distinctive in view of its very
low single scattering albedo (~0.7 at 500 nm) and variable enhanced
absorption at 440 nm.
The strong absorption by this aerosol requires a high black carbon content
while the enhanced blue-band absorption may derive from
organic compounds emitted during the burning of specific vegetation types.
This aerosol exerts a positive radiative forcing
at the top of atmosphere (TOA), with a large deposition of energy in the atmosphere
per unit aerosol optical depth.
This contrasts to the other three classes
where the TOA forcing is negative.
of the four types will be used to improve the representation of
Australian continental aerosol in climate models, and to enhance the accuracy of
satellite-based aerosol retrievals over Australia.
Citation: Qin, Y. and Mitchell, R. M.: Characterisation of episodic aerosol types over the Australian continent, Atmos. Chem. Phys., 9, 1943-1956, doi:10.5194/acp-9-1943-2009, 2009.