A technique for studying aerosol droplets could provide crucial information for global climate modelling. 

Nikolay Jordanov, of the Bulgarian Academy of Sciences and Reinhard Zellner of the University of Duisburg-Essen, Germany, used a technique called optical levitation to study single aerosol droplets containing a mixture of organic and inorganic compounds. The results could provide vital data for use in climate modelling.

 'Aerosol particles in the atmosphere act as nuclei on which water can condense, eventually forming clouds,' explained Jordanov. 'However, pollution of the lower troposphere with organic species can change the properties of natural aerosols, leading to changes in visibility, respiratory problems and effects on climate. There is a lack of knowledge about the behaviour of mixed organic and inorganic particles, but our newly developed technique allowed us to investigate this, using droplets on a micrometer scale.'

The researchers sprayed droplets of ammonium sulphate and glutaric acid into a cell in which the temperature, pressure and relative humidity can be controlled. A single droplet is then trapped in a laser beam. The isolated droplet remains levitating in the beam, without touching any surfaces, and can be analysed using spectroscopy. The researchers say they can determine the dimensions of the droplet and its chemical composition from the data. Jordanov said ammonium sulphate is one of the most important natural aerosols and glutaric acid is an organic species typically found in the atmosphere as a result of human activity. 

Nigel Mason, a physicist at the Open University, UK, said the work is a valuable addition to our knowledge of aerosol properties. 'Today some of the largest uncertainties in our understanding of the processes affecting the Earth's radiative balance and thus the prospect of global warming are linked to our knowledge of the scattering and absorption properties of atmospheric aerosol particles,' said Mason. 'Jordanov and Zellner's work is an excellent example of how a rigorous laboratory study may provide vital data for incorporation into global climate models.' 

Susan Batten