EAS is an aerosol instrument for monitoring and measuring aerosol particle size distribution in the diameter range from 3 nm to 10 µm.
Particle sizing and detection are performed electrically. Particles are charged with ions generated by weak corona discharge. The charged particles are classified in a parallel multichannel mobility analyzer (MDMA) and the classified channel signals are measured by electrometric amplifiers.
The pattern of electrometer channel signals uniquely reflects the sampled aerosol particle size distribution. The deconvolution to particle size distribution is performed in external computer with a special data inversion procedure.
For mathematical details see Development of nanometer aerosol measurement technology (PhD thesis)
|Particle distribution||3 nm to 10 µm|
|Sample flowrate||54 l/min|
|Time resolution||1 second|
|1 - 2 minute averages commonly used during long-term monitoring|
|Power consumption||70 W, AC 110/240 V|
|Dimensions||L 580 mm, W 305 mm, H 810 mm|
|Servicing frequency||1 to 6 months|
|The EAS||From right||Without electrometer shield||From left||From back|
The primary components of the EAS are the two mobility analyzer columns:
- The D-column analyzes fine particles -- sizes from 3 nm to 1 µm
- The E-column analyzes coarse particles -- sizes from 300 nm to 10 µm.
In front of each analyzer is a preconditioning unit which performs aerosol charge neutralization and controlled charging. In the neutralization (or discharging) phase the particles are charged to the opposite electrical polarity than is detected by the mobility analyzer. So the instrument does not need an external neutralizer. After discharging, the particles are charged using a discharger in the D-column and an electric field charger in the E-column.
The suitable size range for D and E analyzers is selected with the combination of controlled charging efficiencies, electric filters and a cyclone. A cyclone in D preconditioning unit has particle cut-off size of 1.5 µm. An electric filter in the E preconditioning unit removes particles smaller than 0.5 µm. Both preconditioning units include honeycomb type flow straighteners.
The mobility analyzer sheath air is taken from the analyzer exhaust air that has been cleaned by electric filters.
The EAS does not use or produce any harmful materials. The aerosol is only treated electrically and electric charging and filtering are processes which happen to particles naturally as well.
The particle size distribution is derived with a mathematical deconvolutiun procedure from the 20 D-electrometers and the 20 E-electrometers. The measured mobility classified channel signals of both columns are combined and deconvoluted together to derive the particle size distribution (particle number density distrbution) in the whole size range from 3 nm to 10 µm.
The measurement process is completely automatic and well controlled. The airflows are driven by three software controlled blowers to compensate for possible obstructions and to take into account air pressure. Particle charging and filtering are also continuosly monitored and adjusted by software.
All parts of the instrument are contained in the single box. The EAS is controlled by an external computer via a RS-232 interface.
Every once in a while the EAS requires cleaning to remove deposited particles from the mobility analyzer and corona needle tips. The cleaning frequency depends on the pollution level and may exceed three month.
EAS is designed for continuous monitoring of ambient air.
Howerer the measurement process is flexible and EAS can be set up to monitor in a wide range of conditions from polluted downtown to fields and deep forest.