Operating principle

The ELPI™ operating principle can be divided into three major parts; particle charging in a unipolar corona charger, size classification in a cascade impactor and electrical detection with sensitive electrometers. The particles are first charged into a know charge level in the charger. After charging the particles enter a cascade low pressure impactor with electrically insulated collection stages. The particles are collected in the different impactor stages according to their aerodynamic diameter, and the electrical charge carried by particles into each impactor stage is measured in real time by sensitive multichannel electrometers. A humidity and temperature sensor is installed in the charger to monitor the sample conditions. All the components are housed in a single compact unit.  Standard RS232 port is provided for communication with a laptop or PC using ELPIVI software, also provided with the instrument. Alternatively, the Outdoor Air ELPI™ can be operated in a standalone mode without the ELPIVI software.

The particle collection into each impactor stage is dependent on the aerodynamic size of the particles. Measured current signals are converted to (aerodynamic) size distribution using particle size dependent relations describing the properties of the charger and the impactor stages. The result is particle number concentration and size distribution in real-time.