Measurement methods: Mass (weight) of particles smaller than 10 µm (PM10) and particles less than 2.5 µm (PM2.5)
One distinguishes between PM10 and PM2.5, ie. the mass of particles less than 10 µm and 2.5 µm, respectively. Another measure of particle contamination, which was often used previously, is TSP (total particulate particulate matter) which also includes larger particles than 10 µm.
The size of a particle is indicated as the 'aerodynamic diameter', ie, the diameter of a spherical particle having a density of 1 g / cm 3, which has the same drop rate as that particle.
10 µm = 0.01 mm, 2.5 µm = 0.0025 mm.
Three methods are described: Gravimetric reference method, Beta-absorption method and TEOM method.
It is common for the methods that the air is sucked in through a particle inlet which separates particles larger than 10 µm or greater than 2.5 µm. The weight of the remaining particles is then determined in one of three different ways:
- LVS - Gravimetric reference method. Daily mean values are determined by collecting the particles on a filter. LVS (Low Volume Sampling) gravimetric determination of PM values occurs by subtracting the weight of the filter without collected particles from the weight of the collected particle filter, and then dividing this particle weight by the air volume that has been sucked through the filter over 24 hours. The weights of the filters with and without collected particulate matter take place in the laboratory, which can lead to up to one month before the final PM results appear.
- Beta-absorption. Daily mean values are determined by collecting the particles on a filter. Immediately after collection, the weight is determined on the basis of absorption of beta particles in the dust layer. Each week, the exposed filters are sent to DCE's laboratory. Some of the filters are used to analyze the content of the elements in the dust.
- TEOM. Half-hourly values are determined with TEOM (Tapered-Element Oscillating Microbalance). The air is sucked through a filter which sits at the end of a conical rod which is electronically vibrated. The vibration frequency depends on the weight of the dust on the filter (similar to the pitch of a tuning fork). For the sake of the stability of the measurements, the system is kept at a relatively high temperature in relation to the ambient air temperature. Hereby, some of the volatile compounds in the dust are lost. Generally, the loss is 20-30% of the original mass. The TEOM method, on the other hand, has the advantage of being able to obtain measurements with high time resolution.
Note about TEOM: The results for the TEOM method are not necessarily directly comparable to the other two methods, and results from the TEOM method cannot be directly compared to the EU limit values. However, the EU Commission accepts for PM10 that TEOM results multiplied by 1.3 are valid for comparison with the limit values.
When DCE indicates results for particle concentration measurements, it is usually clearly indicated if the TEOM method is used.
- What measurement results are displayed for PM10 and PM2.5? Some details about changing measurement methods and measurement unit. It elaborates on what measurement results the web page Database lookup gives access to.
- Measuring method for TSP (suspended matter)
- Limit values