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Airborne Aerosol Measurements and Analysis.
Dr Jim McQuaid and
Dr Barbara Brooks
Background: The direct and indirect radiative climatic forcing by aerosols currently has a very high profile in
atmospheric science and is a high priority area of UK Atmospheric science at present. This project would feed directly
into this area of research. The detailed compositional information will enhance the knowledge of the cloud droplet nucleating
ability of aerosols under different composition regimes. Furthermore analysis of VACC data will provide additional input into
the climatologically important field of direct and indirect forcing by aerosols on both regional and global scales.
The chemical partitioning across the size distribution can provide evidence for aerosol processing and ageing through analysis of
the modality across the thermal range.
The Leeds airborne Volatile
Aerosol Concentration and
Composition (VACC) is a unique instrument in the UK.
It is a proven technique which relies upon the fact that specific aerosol are volatilised using a heater system which is
coupled to a PCASP-X aerosol spectrometer (O’Dowd and Smith 1993). Therefore it is capable of producing
size distributions as a function of volatility and can thus provide information on the chemical
composition in terms both number and size. The system has been used to identify sulphate, sea-salt, soot and methanesulphonic
acid (MSA) aerosol components, providing size-differentiated information in near real-time.
In
addition a very useful feature of the VACC instrument is capable of providing
information on the mixing state of the aerosol population. Knowledge of the mixing
state is important for adequate prediction of both the direct (through optical
properties) and indirect (through cloud droplet nucleating ability) radiative
effects of atmospheric aerosols. The mixing state of aerosol particles can be
characterized by two extreme microphysical properties: external mixtures, where
individual particles consist of a single chemical species, and internal mixtures,
where all particles contain a mixture of different species.
The instrument has been successfully
installed onto the new UK research 146 aircraft and has already been operated during recent
field campaigns (ADRIEX, RICO
DABEX and
T-REX).
With the advent of new instruments such as the Aerodyne Aerosol Mass Spectrometer (AMS) to provide highly detailed information
on the aerosol composition namely their mass loadings with respect to their aerodynamic size benefits significantly from the
'broader' picture which the VACC can generate. Coupled together the data produced by these systems will culminate in exceptionally
powerful tools for increasing our understanding of atmospheric aerosol processes.
This project will address the areas of data analysis
of existing and future datasets and also future data collection by employing
a motivated and highly skilled research student. This project will only to investigate
VACC data but also to integrate it into other aerosol data generated on the aircraft
(eg. AMS, PMS probes, filter bulk samples, CCN).
In particular specialised data analysis tools will be generated to identify the mixing status of sampled aerosol whether they are
internally or externally mixed. Further development of the VACC instrument rack will bring online a scanning mobility particle sizer,
this will provide number concentration across the ultrafine aerosol region, such a measurement is not currently available on the 146
aircraft and this project will integrate this additional measurement into the aerosol data ensemble.
Research Details: The research project is primarily one of numerical analysis of both existing and future data generated by the
VACC in conjunction with other measurements made on-board the 146 aircraft. In addition you will participate in the field detachments
gaining invaluable first hand experience of the collection of such comprehensive datasets. You will be actively involved in mission
planning of the flights and taking a role as mission scientist, this will allow you to get involved in data collection at the outset
and then follow its path through to final products and model comparisons.
Potential future deployment involving the VACC instrument include VISURB (UK
Visibility – Met Office) and the UK component of the International COPS
(Convective and Orographically-induced Precipitation Study). In addition the
VACC is involved in proposed airborne missions under the APPRAISE program (ADIENT).
These opportunities will further provide access to a wide range of aerosol types
and compositions for VACC analysis.
Further laboratory development of the VACC instrument rack will bring online
a scanning mobility particle sizer (SMPS) which will provide number concentration
across the ultrafine aerosol region; such a measurement is not currently available
on the 146 aircraft and this project will integrate this additional measurement
into the aerosol data ensemble. Access to the ultrafine (Aitken) mode via the
SMPS will provide detailed knowledge of the aerosol that grows into the accumulation
mode where the CCN and optically-active particles reside.
The microphysical and chemical data provided by the VACC and complimentary
instruments fitted to the aircraft are an important part of aerosol microphysics-radiation-cloud
microphysics closure that can be investigated using a combination of observations
and modelling studies. Size resolved compositional data of aerosol in the 1 micron
region is critical to the closer understanding of both the growth rates of an
aerosol and the optical properties of the particle.
Project Research Details: The research project is one of
numerical analysis of both existing data (ADRIEX, RICO, DABEX and DODO) and data
to be collected during the forthcoming ADIENT and EUCAARI. Fieldwork funds are
requested for participation in a field experiment in 2008/9 (ADIENT) . Having
access to existing datasets will allow the student to proceed to the data analysis
at the outset of the project and the proposed campaign participation will allow
the student to become involved in the data collection then follow its path through
to final products and model comparisons. It is felt that this is particularly
beneficial, allowing the student to work directly with other scientists specialising
in satellite and ground-based observations in addition to those involved directly
in the present subject matter. Therefore there is the opportunity to interact
and collaborate with people from differing backgrounds.
By assimilating the VACC data into the aircraft master aerosol dataset it will
be possible for the data analysis to investigate the following aspects of aerosols:
- specialised data analysis tools will be used to identify the mixing status
of sampled aerosol whether they are internally or externally mixed; this knowledge
is of prime concern when modelling the optical and CCN properties of aerosols;
- comparison of the microphysical and chemical properties of different aerosol
types i.e. dust, industrial, biomass burning;
- closure study of aerosol chemistry between VACC, filters and AMS; this leads
to a comprehensive description of aerosol composition;
- a subsequent closure study of the aerosol chemistry, microphysics and optical
properties both through measurements and modelling (e.g. using theoretical
Mie scattering codes)
This project provides a unique opportunity to combine numerical analysis and
aerosol measurement.
References and further reading:
Carrico, C.M., M.J. Rood, J.A. Ogren, C. Neusus, A. Widensohler & J. Heintzenberg
(2000): Aerosol optical properties at Sagres, Portugal, during ACE-2. Tellus,
52B, 694.
IPCC (Intergovernmental Panel on Climate Change) 2001: Climate change 2001:
The scientific basis. Houghton, J.T., Y. Ding, D.J. Griggs, M. Noguer, P.J. van
der Linden, X. Dai, K. Maskell amd C.A. Johnson (eds). Cambridge University Press,
Cambridge , UK and New York , USA .
Lohmann, U. & J. Feichter, 2005, Global indirect aerosol effects: a review.
Atmospheric Chemistry and Physics, 5, 715
O'Dowd C.D., Lowe J.A., Smith M.H., & Kaye A.D., 1999, The relative importance
of non-sea-salt sulphate and sea-salt aerosol to the marine cloud condensation
nuclei population: An improved multi-component aerosol-cloud droplet parametrization, Q.J.
Royal Met. Soc., 125, 1295-1313.
Russell, P.B., P. Hobbs & L. Stowe, 1999, Aerosol properties & radiative
effects in the United States East Coast Haze Plume: An overview of the Tropospheric
Aerosol Radiative forcing Observational Experiment, J.Geophys.Res, 104,
2213.
Osborne , S., Haywood, J. and Bellouin, N. 2006: "In-situ and remote sensing
measurements of the mean microphysical and optical properties of industrial pollution
aerosol during the Aerosol Direct Radiative Impact Experiment (ADRIEX)".
Submitted to Quart. J. Roy. Meteorol. Soc. for ADRIEX Special Issue.
Highwood, E.J., Haywood, J.M., Coe, H., Cook, J., Osborne , S., Williams, P.,
Crosier, J., Bower, K., Formenti, P., McQuaid, J., Brooks, B., Thomas, G., Grainger,
R., Barnaba, F., Gobbi, G.P., Leeuw, G. de, and Hopkins, J., 2006: "Aerosol
Direct Radiative Impact Experiment (ADRIEX) Overview". Submitted to Quart.
J. Roy. Meteorol. Soc. for ADRIEX Special Issue.
Brooks , B.J., McQuaid, J.B., Smith, M.H., Crosier, J., Williams, P.I., Coe,
H. and Osborne , S., 2006: "Inter-Comparison of VACC and Aerosol Mass Spectrometer
derived Nitrate, Sulphate and Ammonium Aerosol Loadings during ADRIEX".
Submitted to Quart. J. Roy. Meteorol. Soc. for ADRIEX Special Issue.
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