A Multi-Channel Expansion Type Condensation Particle Counter

The influence of atmospheric aerosols on the evolution of the global climate and on human health has recently received considerable attention. Many research groups are presently studying the influence of charged molecular clusters and ionizing radiation on the formation of nanoparticles in the atmosphere and thus on cloud formation and climate. In this connection as well as for various other applications accurate determination of aerosol properties is of great importance. Particularly particles in the size range above approximately 1 nm diameter play a decisive role in new particle formation processes. So far practically no measuring instruments are available in the particle size range around 1 nm. In recent years we have developed an expansion chamber measuring system, the Size Analyzing Nuclei Counter (SANC). Using this device and with the financial support of the FWF we have performed various experimental research projects on nucleation and condensational growth in supersaturated vapours. In recent weeks we for the first time succeeded to detect particles and ions with diameters down to 1 nm by means of the SANC. Publication of these results is presently in preparation. The SANC is currently set up as a measuring system in the laboratory and can only be used for laboratory measurements. For many applications, however, the use of a mobile measuring system would be extremely important. Particularly a measuring system with a number of simultaneous measuring channels would provide a variety of additional applications. Continuing our previous experimental research work we plan the development of a Mobile SANC with 1 measuring chamber (MSANC) and of a mobile Multi-Channel SANC with 4 chambers (MCSANC). In this connection we can use our experience gained from previous research projects. With the cooperation of an experienced Ph.D. student the planned work can be performed within the envisaged time period. The development of the software required for process control, data acquisition and data reduction will be performed within corresponding contracts for work and labor. The proposed project would provide the opportunity to subsequently participate in very timely cooperative experiments. There is considerable interest in using a mobile SANC at experiments on the influence of ionizing radiation on the formation of nanoparticles in the atmosphere (CLOUD cooperation, CERN, Geneva). Furthermore it is planned to use a mobile MCSANC in background measurements of atmospheric aerosols, where particularly the influence of charged and uncharged molecular clusters on the dynamics of atmospheric particle new formation will be studied (research station Hyytiälä, University of Helsinki, Finland). The planned use of the MSANC and MCSANC at international projects bears considerable innovative potential. At this point a commercial financing partner is not yet involved. After completing the development of the planned prototypes it is intended to contact a number of manufacturers in order to investigate concrete possibilities of commercially utilyzing the newly developed instruments.

Despite considerable world-wide research efforts the influence of aerosols and clouds still causes the highest uncertainty in our current understanding of climate change. Particle formation processes in the atmosphere are frequently related to freshly nucleated molecular clusters with diameters of the order of 1 2 nm. Therefore one focus of the present project was placed on the development of a measurement system capable of detecting, counting and investigating molecular clusters and aerosol particles in the nanometer size range.In a joint research effort at CERN, Geneva, we studied homogeneous nucleation in multicomponent vapour mixtures under precisely controlled concentrations of water vapour, sulfuric acid vapour and other compounds in the CLOUD chamber. Stable sulfuric acid concentrations were achieved applying an innovative fibre-optic UV system. Results show that atmospheric boundary layer nucleation can be accounted for, if besides sulphuric acid and ammonia in addition certain organic trace compounds are considered as well.Atmospheric particle formation can be explained by heterogeneous nucleation on freshly nucleated molecular clusters. In this project we have therefore considered some basic aspects of heterogeneous nucleation. This involves careful experiments on contact angles. Furthermore we performed theoretical studies on the influence of electrical charge of the seed particles on the heterogeneous nucleation process.Recently we discovered strange temperature effects for heterogeneous nucleation. In this project we studied the temperature effect for water vapour. The experimental results reveal unexpected behaviour, which can tentatively be related to strong molecular-scale interactions at the seed particle surface. Furthermore the vapour supersaturations required for activation of seed particles were found to be well below previous theoretical expectation according to the generally accepted Kelvin equation. As a consequence the widely used term "Kelvin diameter" needs to be critically reconsidered and the fundamental detection range of Condensation Particle Counters is extended to particle diameters as small as 1 nm.A central aspect of this project was the design and construction of a novel condensation particle counter, the versatile Size Analyzing Nuclei Counter (vSANC). Vapour supersaturation in the vSANC is achieved by adiabatic expansion. Software systems for process control and data evaluation have been developed and tested. The vSANC has been carefully characterized. An important feature of the vSANC is its portability. The vSANC has been installed for several months at the background measurement station in Hyytiälä, Finland and applied for experimental observations of atmospheric nanocluster concentrations.