Aerosols as an important link between large scale land-use modification and subsequent regional climate change: an experimental approach

W. Junkermann¹, J. Hacker², T. Lyons³ and Udaysankar Nair⁴

¹FZK, IMK-IFU, Garmisch-Partenkirchen, 82467, Garmisch-Partenkirchen, Germany

²Airborne Research Australia, Flinders University, Adelaide, Zip Code, City, Australia

³Murdoch University, South Street, Murdoch, 6150, Murdoch, WA, Australia

⁴National Space Science Technology Center, Huntsville, Alabama, 35805, USA

Keywords: Nucleation, Aerosol Size Distribution, Aerosol Characterisation, Cloud condensation nuclei

Fine particles act as an important link in the planetary boundary layer between surface water budget and cloud microphysics and subsequently precipitation. The number of cloud condensation nuclei within the planetary boundary layer originating either from advection or from local production of particles controls the droplet size distribution in the clouds and may also effectively modify precipitation probability. It affects cloud albedo and the radiation balance in a cloudy atmosphere (Flossmann, 1998) Land use, surface structure and vegetation will significantly modify the local population of aerosols as well from wind blown dust which consists mainly from coarse particles as well as from local particle production from gas phase precursors which produces fine and ultrafine particles. It has been shown that ultrafine particles from nucleation can be a significant source for cloud condensation nuclei even in otherwise already heavily polluted environments (Laaksonen et al, 2005). In clean environments nucleation is considered to be the main source for particles in the accumulation mode. As modifications of the water budget have to be expected with climate change and are critical for future land use and agriculture, climate models need detailed information on the distribution of particle sources and source strength. New particle production and growth has been attributed to reactions of sulphur components and volatile organic compounds in the norther hemisphere. In the southern hemisphere measurements are sparse and due to the lower sulphur concentrations new particle production might be different. Measurements were performed in a huge natural laboratory in south-western Australia in the area of Lake King close to the vermin proof fence which divides the area into homogeneous agricultural and natural vegetation. The area was shown previously to develop clouds above either the agriculture or above the natural vegetation on several occasions. The location allows to perform regional scale measurements comparing the different land use and surface structure and their impact on the local aerosol population within the planetary boundary layer using instrumented aircraft as mobile research platforms. Two small aircraft were involved in the study equipped with instrumentation for aerosol size distribution, surface albedo, radiation balance and turbulent fluxes of water and CO2 as well as with remote sensing equipment for land surface characterisation. A considerable local production of new particles has been found above the harvested agricultural land and the scattered salt lakes in the area while nucleation could never be observed above the natural vegetation. The result is a two fold concentration of CCN with significant impact on cloud microphysics.

The paper discusses the data from two campaigns in different seasons and possible implications on the regional climate in this area.

Flossmann, A. I. (1998). J. Atmospheric sciences, 55, 879-887.

Laaksonen, A., Hamed, A. Joutsensaari, J., Hiltunen, L., Cavalli, F., Junkermann, W., Asmi, A., Fuzzi S., and Facchini,M.C.(2005) Geophys. Res.Lett.,32,6,

L06812, 10.1029/2004GL022092,