Measurement Methods II

How to detect, collect and analyse aerosol particles.


The concept of TSP, PM10, PM2.5 and UFP

Particle Collection

Particle Counters

Other methods

Aerosol Analysis

A selection of links


The concept of TSP, PM10, PM2.5 and UFP

TSP: Total Suspended Particulate

As the name suggests, TSP are all aerosol particles (sometimes even above 100 mm sizes) suspended in the air.

PM10 and PM2.5

PM10 means particulate mass of particles smaller than 10 mm in diameter and consequently PM2.5 means particulate mass of particles smaller than 2.5 mm in diameter.

The reason for these two size categories is that particles smaller than 10 mm are respirable, that is, they can be inhaled below the nasopharynx area (nose and mouth), and particles below 2.5 mm travels down below the tracheobronchial region (into the lungs). The PM2.5 cut off size also coincides with both the local minimum in particle concentration between coarse and fine particles and the natural and anthropogenic fractions.

The fraction of PM10 larger than PM2.5 is often called coarse particles and PM2.5 is often called fine particles.

Ultra Fine Particles (UFP)

Ultra fine particles are particles with an aerodynamic diameter less than 0.1 mm. In recent years this size fraction has come into focus due to the new found link between these particles and health effects in form of respiratory problems such as asthma, inflammatory diseases and reduced oxygen uptake efficiency.

Particle Collection

Filter cups

Using filter cups to collect particles is the simplest way of collecting particles. Weighing the filters before and after the sampling gives the amount of particulate mass collected, and by knowing the amount of air drawn through the filter the mass concentration can be calculated. The downside is that if no size-limiting inlet has been used, the particle size limit is not known.


Cyclones are a special type of impactors where the impaction (on the side walls of the cyclone) is combined with the gravitational settling of the large particles. The effect is that the large particles will get trapped before they reach the collecting filter and thus giving a cut off size dependent of the size, geometry and air flow velocity through the cyclone.

Cyclones (often) have the advantage of being both small and cheap but still accurate enough for most modern requirements.






Virtual Dichotomous Impactor

This type of impactor uses a virtual impaction stage to separate between sizes, letting the particles continues down to be collected on a filter. It is a two-stage impactor (hence the name dichotomous) dividing the particles into two size ranges, 10 – 2.5 mm and less than 2.5 mm.




Cascade Impactors

Cascade impactors are consists of a number of impactor stages connected in series with smaller and smaller cut-off diameter. The cut-off diameter in each stage depends on the air velocity and geometry of the stage (i.e. the distance from the nozzle to the impaction plate). Cascade impactors often have up to some ten stages ranging from a cut-off diameter on the first stage of 10 – 30 mm to a diameter of 0.1 mm or lower on the backup filter in the end. This gives the opportunity to analyse (e.g. chemical or gravimetrical) a number of small size intervals. Some drawbacks are the risk of bounce off from one stage to the next (i.e. particles of wrong size at some of the stages) as well as the problem of obtaining sharp cut-off diameters in the last stages (cut-off diameter less than 0.1 – 0.2 mm). Coating the impaction plates with oil or some other sticky substance, which catches the particles more effectively, can reduce the risk of bounce of. This will then prevent or severely complicate direct mass concentration calculations of the different stages.



Particle Counters

Aerodynamic Particle Sizer (APS)

The APS is used for measurement of size distributions of particles in the size range 0.5–20 mm aerodynamic diameter. The instrument both counts and measures the size of the particles using the properties of the particle (light scattering and settling velocity).






Condensation Particle Counter (CPC)

The CPC counts particles with a diameter of a few nanometres up to about one micrometer. It is very hard to optically detect sub micron particles since the diameter is equal or smaller than the wavelength of light; the diameter of the particles has to be increased before detection. This is accomplished by letting the particles pass through a “cloud” of evaporated alcohol witch attach to the particle and makes much larger and easy to detect/count. This uncontrolled increase makes it impossible to size classify the particle.





Differential Mobility Particle Sizer (DMPS)
Scanning Mobility Particle Sizer (SMPS)

The DMPS and SMPS are basically the same type of instrument with only different electronic control mechanism. It consists of a DMA (Differential Mobility Analyser), a CPC and some electronic controlling devices, everything controlled by a PC. As mentioned before, the CPC is unable to size classify the particles since it cannot determine the original size before the “cloud”. This is now taken care of by the DMA, an apparatus capable of selecting only a very narrow size fraction of particles that then enters the CPC. The CPC counts the number of particles as usual and since the size is already determined, information of both concentration and size is obtained. By changing the setting of the DMA, scanning over the whole particle size interval (3 nm to 1 mm) is possible.




Other methods

Electrical Low Pressure Impactor (ELPI)

The ELPI enables real time particle size distribution and concentration measurement in the size range from 30 nm up to 10 mm. It is intended for any application where a wide size range and fast response time are required.

The ELPI is based on combining electrical detection principles with low-pressure impactor size classification. The electric current carried by charged particles into each impactor stage is measured in real-time by a sensitive multichannel electrometer. By using this instrument it is possible to measure size distribution and concentration even when the concentration varies rapidly.




Tapered-Element Oscillating Microbalance (TEOM)

The TEOM is a real-time instrument for measuring the mass concentration of particulate matter smaller than 10 mm in ambient air.

The instrument uses a vibrating collection substrate to collect the particles. The change in “load” or sample mass will change the frequency of oscillation and that is used to calculate the mass concentration.

The TEOM can measure particulate concentration in the range from 5 mg/m3 up to several mg/m3.




Aerosol Time Of Flight Mass Spectrometer (ATOMFS)

ATOFMS is the first instrument to offer the ability to determine size and chemical composition of individual particles in near real-time.

The instrument detects and analyse particles in the size range from 0.3 to 3 mm. It can be described as an APS followed by a time-of flight mass spectrometer.





A selection of links


Aerosol Analysis

When the aerosol is collected a number of different methods and techniques exists to get more information about the aerosol. The simplest is to weigh the sample to get the mass concentration, but often more information is needed. Depending of the questions addressed, the way of collection method, available instruments and a number of other aspects (money!!!) different analysis options are of interest.


Below is as short list of some of the more common analytical techniques in the field.


Analytical method


Type of Information

Energy Dispersive X-Ray Fluorescence spectrometry



Total Reflection X-Ray Fluorescence spectrometry



Atomic Absorption Spectrometry



Mass Spectrometry



            Inter Coupled Plasma MS



            Gas Chromatography (-MS)


Organic Compounds

Neutron Activation



Anodic Stripping Voltammetry



Electron Spectroscopy (for chem.. analysis)



Ion Chromatography


Inorganic compounds

Selective Ion Electrodes





Inorganic compounds

IR-, UV- Spectroscopy