Aerosol Instrumentation

To probe the properties of aerosol particles of atmospheric or technological importance we often need to develop our own instruments and experimental setups. These arrangements involve electrical mobility analyzers for measuring the size and other size-dependent properties of the particles, such as volatility and hygroscopicity.

Aerosol Spectrometers

Electrical mobility analysis is the most efficient technique for measuring the size of particles having diameters in the sub-micrometer range. In this technique, charged particles are classified in an electrostatic field based to their electrical mobility. Examples of electrical mobility spectrometers include the widely used Scanning Mobility Particle Sizers and the Differential Mobility Analyzer (cf. Fig. 2; Biskos et al. 2005).  

Tandem Mobility Analyzers

A relatively simple and cost-effective way to probe size-dependent properties of aerosol particles in real time is to use mobility analyzers it a tandem configuration (cf. Fig. 3). In these systems, a flow of monodisperse particles produced by a first mobility analyzer (i.e., a Differential Mobility Analyzer; DMA) is passed through a reactor where they are subjected to conditions that can alter their size (e.g.,  high temperature or humidity). The size distribution of the particles exiting the reactor is measured by a second mobility analyzer coupled with a detector.

To probe properties of aerosol particles such as hygroscopicity and volatility we commonly develop and use Tandem DMA configurations in our laboratory and field studies (e.g., Biskos et al. 2009). One great advantage of this systems is its high time resolution (i.e., of the order of a minute) which is very important when measuring airborne particles in the field.

Figure 2. Schematic layout of the Differential Mobility Spectrometer. Incoming aerosol particles are initially charged within a unipolar diffusion charger before getting into the classification section that consists of two concentric electrodes between which a potential difference is applied. Within the classification section, the charged particles are deviated towards the outer electrode where a series of isolated rings connected to sensitive electrometers for measuring their concentration is located. Particles of different electrical mobilities are deposited on different electrometer rings along the classification column.

Figure 3. Schematic diagram of the Tandem DMA experimental setup. Particles having diameter within a very narrow range selected by the first DMA are passed through the aerosol reactor where they are exposed to different conditions. The size distribution of the particles exiting the reactor is measured by the second DMA coupled with a particle detector. Comparison of the size distribution of the particles before and after the aerosol reactor can provide insights to the processes under investigation.

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