Method and device for the measurement of the number concentration and of the average diameter of aerosol particles
According to the invention, particles of an aerosol are firstly charged in a unipolar manner in a diffusion charger ( 10 ). They are subsequently led through a diffusional precipitator ( 20 ) in which a part of the particles is precipitated. The diffusional precipitator current is measured and a value for the number concentration is evaluated from the current. A single diffusional precipitator may be used for this. According to preferred embodiment, a means for measuring the influence current and/or an aerosol electrometer are additionally present, by way of which one may measure a complete current. The latter additionally permits the evaluation of the average particle size. Additionally, one may determine an elementary carbon total quantity from the average particle size with the help of a measurement of the photoelectric charging carried out in parallel.
1. A method for measuring an integral total number concentration of particles in an aerosol, wherein the aerosol contains particles of an unknown size distribution, the method comprising the steps of:
electrically charging the aerosol by way of diffusion charging to create charged aerosol particles;
measuring a diffusional precipitator current which is caused by at least some of the charged aerosol particles being precipitated in a single diffusional precipitator or in a plurality of diffusional precipitators connected electrically in parallel or in a plurality of diffusional precipitators arranged in parallel with regards to an aerosol flow, and
evaluating a value for the integral total number concentration based on a result from said measurement,
wherein the said diffusional precipitator current is measured from a single diffusional precipitator and is the only diffusional precipitator current used in said step of evaluating the value of the integral total number concentration.
2. The method according to claim 1 , wherein the charging of the aerosol is effected by way of a unipolar diffusion charger.
3. The method according to claim 1 , wherein a single diffusional precipitator is used.
4. The method according to claim 1 , wherein the diffusional precipitator is designed as a plate precipitator, as a grid precipitator, as a tube precipitator or as a combination of at least one of a plate precipitator, a grid precipitator and of a tube precipitator.
5. The method according to claim 1 , comprising the additional step of compensating an influence current which possibly arises in the diffusional precipitator, the step of compensating the influence current including measuring an influence current in an additional electrode, wherein for the calculation of the value for the number concentration, the current measured in the additional electrode is used as a further input value in addition to the result of said measurement of the diffusional precipitator current, said additional step being performed upstream or downstream or in parallel to the step of measuring said diffusional precipitator current.
6. The method according to claim 5 , wherein a geometric shape of the additional electrode corresponds to a geometric shape of the diffusional precipitator without precipitation surfaces.
7. The method according to claim 5 wherein the diffusional precipitator and the additional electrode are provided in a serial arrangement and are flowed through consecutively.
8. The method according to claim 1 comprising the additional step of measuring a total current of the diffusion charged aerosol, and of determining the average diameter of the particles from this total current and the diffusional precipitator current.
9. The method according to claim 1 comprising the additional step of compensating an influence current which possibly arises in the diffusional precipitator, the step of compensating the influence current comprising measuring an influence current in an additional electrode, wherein for the calculation of the value for the number concentration, the current measured in the additional electrode is used as a further input value in addition to the result of said measurement of the diffusional precipitator current, said step of compensating the influence current being performed upstream or downstream or in parallel to the step of measuring said diffusional precipitator current, and further comprising the additional step of measuring a total current of the diffusion charged aerosol, and of determining the average diameter of the particles from this total current and the diffusional precipitator current.
10. The method according to claim 9 , comprising the additional steps of charging, in a separate measurement line, particles of the aerosol photoelectrically, of determining the charging and of computing an elementary carbon total quantity from this and the average particle diameter.
11. The method according to claim 1 comprising the additional step of measuring a total current of the diffusion charged aerosol, and of determining the average diameter of the particles from this total current and the diffusional precipitator current, and further comprising the additional steps of charging, in a separate measurement line, particles of the aerosol photoelectrically, of determining the charging and of computing an elementary carbon total quantity from this and the average particle diameter.
12. The method according to claim 1 , wherein the value for the number concentration is determined, in that the current in the diffusional precipitator is multiplied by a calibration factor and where appropriate is corrected by way of correction values gained from measurements of at least one of the influence current and of the total current.