Aerosol Generation & Conditioning
Producing a reproducible test aerosol of known size distribution and concentration, then conditioning it — drying, neutralising, diluting, transporting — so that whatever measures it downstream sees what the method actually intended.
Test-Aerosol Definition and Control
In almost every filtration or contamination measurement, the aerosol is the known quantity against which the unknown is judged. If its size distribution, concentration or charge state drifts, the measurement drifts with it — and nothing downstream can recover the error.
- Particle size rangeWhether the method needs the Most Penetrating Particle Size, a defined monodisperse size, or a broad dust distribution.
- Concentration and stabilityHigh enough to measure through the filter, stable enough to hold across the test duration.
- SubstanceLiquid such as DEHS or PAO, solid such as PSL or a test dust, chosen for the method and permitted on site.
- Charge stateFreshly generated aerosols carry charge that can bias filtration results until it is neutralised.
- MoistureSuspension aerosols must be dried so the residual particle, not the droplet, reaches the test object.
- DeliveryFlow, counter-pressure and transport route to the point of use without losing the distribution to the tubing.
Governing references
VDI 3491Measurement of particles — preparation and dilution of test aerosols ISO 21501-4Only where the aerosol is used to evaluate or calibrate an optical particle counterEN 1822 and ISO 29463 are not aerosol-generator standards. They belong to the downstream filter application the aerosol feeds — see Filter Development & Production Testing →
Aerosol Generation and Conditioning Architecture
Not every application needs every stage. The chain below is the full set; a given method uses the subset its test object and standard require.
Drying applies where a suspension is atomised and only the solid residue is wanted. Neutralisation applies where charge would bias the result — filtration efficiency measurements in particular. Dilution applies where the concentration exceeds the working range of the instrument that has to measure it.
Aerosol Generation Principles
The principle follows the substance and the size distribution required.
ATM 226Polydisperse liquid aerosol by two-stream pneumatic atomisation.- 70 – 300 L/h
- 0.5 – 2.5 g/h
- Integrated compressor
SAG 410 SeriesReproducible dust and powder aerosol by controlled dosing.- Solid particles
- Modular dosing
- Filter / separator testing
SLG 270Monodisperse aerosol by controlled condensation.- Monodisperse
- Condensation principle
- Narrow distribution
ATM 240/LPSL and solid-particle aerosol from suspension with integrated drying.- PSL suspensions
- 10,000 – 24,000 L/h
- Integrated drying
Aerosol Conditioning: Dilution, Drying and Neutralisation
A generator's output is rarely what the instrument downstream can accept directly. Conditioning brings the aerosol into the range and state the measurement requires, while preserving a known relationship to what was generated.
Dilution is the stage that appears most often, because reference measurements frequently need concentrations far above a particle counter's working range. A defined dilution factor is what makes the reduced sample traceable back to the real concentration.
- DIL 55428.3 L/min at 1:100 — the base configuration.
- DIL 554/H56.6 L/min at 1:100 — for a higher counter flow.
- DIL 554/Z28.3 L/min at 1:10 — for a lower dilution factor.
- DIL 554/T28.3 L/min at 1:100 with a 1/4″ hose connector.
The variants are not interchangeable: the flow must match the sample flow of the particle counter actually used, and the dilution factor must suit the concentration being reduced. A family figure does not describe every member of the family.
Dilution in the filter-integrity chain →
Applications
Aerosol generation is rarely the end goal — it is the enabling stage for a measurement happening somewhere else. These are the routes it most often feeds.
Standards and Application Context
Aerosol engineering guidance applies here. Filter-performance and cleanroom-installation standards belong to the applications this stage feeds, not to the aerosol stage itself.
| Reference | Edition / status | Role |
|---|---|---|
| VDI 3491 | Current published reference | Measurement of particles — preparation and dilution of test aerosols |
| ISO 21501-4 | 2018 (Edition 2) + Amendment 1:2023 — Current published reference | Where the aerosol is used to evaluate or calibrate an optical particle counter |
Scroll the table horizontally →
Topas cites VDI 3491 sheets 1, 2 and 15 in its cleanroom test equipment documentation. Confirm the individual sheet number and issue date before citing it on a project document.
Configure an aerosol generation and conditioning chain
Share the test aerosol required, the size distribution and concentration, the flow and counter-pressure, the conditioning stages needed and the instrument that has to measure it.