Not to go into scientific details of measuring the content of suspended particulate matter in the air, it is worth keeping in mind that these tests are very complex. To precisely determine the content of suspended particulate matter, it is required to provide the number or mass of particles of a given type for every unit of air volume. It is widely accepted to divide the particulate matter into, dust falling – with the particle diameters larger than 10 μm – and suspended particulate matter with the particle diameters smaller than 10 μm. Such a particle size division has not been set loosely. It has to be remembered that particles of the size smaller than 10 μm are small enough to penetrate deep into the respiratory tract and lungs, and pose a real threat to the health. Of course not all particles are very harmful – suspended matter differs strongly in physical and chemical composition, source, and size of the particles.
Additionally, suspended matter – so that of particle sizes smaller than 10 μm in diameter – is divided into coarse particles – with the particle diameter larger than 2,5 μm (but smaller than 10 μm), and fine particles with the diameter larger than 0.1 μm but smaller than 2,5μm. The term diameter is used conventionally – the particles have irregular shapes, and are compared by reference to a spherical particle with the same aerodynamic properties as the real particle.
PM2.5 particulate matter includes particles with the diameter smaller than 2.5 micrometers, which may reach the upper respiratory tract, lungs, and penetrate into the blood. The target annual value of the PM2.5 particulate matter is 25 ug/m3, the acceptable level is at 25 ug/m3, and the acceptable level with an added tolerance margin for the year 2012 – 27 ug/m3. The largest particulate emission is caused by burning coal in old, often not adjusted boilers and heaters, and by traffic in large cities. Burning waste, even though it is illegal and causes serious harm to the health, is still practiced by some. Particulate matter is also produced by the industries, especially energy, chemical, extraction, and metallurgy. However, due to the height of the emission sources, as well as provisions of law regulating the acceptable emission values, these sources have usually much less of an impact on the quality of air.
Particulate matter with the diameters smaller than 10 micrometers is absorbed in the upper respiratory tract and bronchi. Inhaled to the lungs, it may cause various reactions, for example coughing, difficulties in breathing, and shortness of breath, especially during physical effort. It contributes to enhancing the risk of infections of the respiratory tract, and the exacerbation of allergy symptoms, for example asthma, hay fever, and conjunctivitis. The exacerbation depends heavily on the concentration of the particulate matter in the air, exposure time, additional exposure to environmental factors, and individual vulnerability. Minor fractions of the particulate matter may penetrate into the bloodstream, while a longer exposure to a high concentration may have a serious impact on the course of a heart disease (high blood pressure, heart attack), or even enhance the risk of various cancers, especially concerning the lungs. Recent data confirms a harmful impact of the inhaled matter on the health of pregnant women and the fetus (low birth weight, inborn defects, pregnancy complications).
The particulate matter with diameters smaller than 2.5 micrometers (the so called fine particles), is absorbed in the upper and lower respiratory track and may also penetrate into the blood. Similarly to the PM10 particulate matter, it may cause coughing, difficulties in breathing, shortness of breath, especially during physical effort.
The PM10 consists of a combination of suspended particulate matters, being a combination of organic and inorganic substances. The suspended particulate matter may include toxic substances such as polycyclic aromatic hydrocarbon (for example benzo[a]pyrene), heavy metals, as well as dioxins and furans. PM10 includes particles with their diameters smaller than 10 micrometers which may reach the upper respiratory track and lungs. The acceptable daily concentration is 50 ug/m3 and may be exceeded no more than 35 days a year. The acceptable annual concentration is 40 ug/m3, and an alarm level is set at 200 ug/m3.
The suspended particulate matter may additionally be divided due to the location of the respiratory system, which it reaches:
- Inhalable particles – particles breathed through the nose and mouth
- Thoracic particles – particles reaching further than the larynx
- Respirable particles – particles penetrating into the alveoli
Three main groups of methods for measuring the content of suspended particulate matter, may be distinguished: gravimetric, optical, and microbalance. Of course this classification does not limit the classification of a vast number of measuring methods.
Gravimetric methods are regarded as the most precise, and are used most widely as referential methods. In gravimetric methods, air passes through a measurement chamber which includes a set of filters. Basing on the weight of the filter before and after the measurement, but also the amount of air pumped through the chamber during the test, the amount of suspended particulate matter is determined. This measurement method is widely used in Europe or the USA. In Poland, gravimetric measurements are conducted in circa 160 measuring stations for the PM10 particulate matter, and about 60 stations for the PM2.5. The precision of this method is achieved at the cost of time and price of the test. The complex process of preparing filters in controlled conditions, transport to/from the measuring station, and the need to precisely measure the weight at a laboratory, are the main disadvantages of this method.
Optical methods base on illuminating the particles with a beam of light and analyzing the accompanying phenomena. Methods basing on the measurement of reflected light are widely used. Devices which work basing on optical methods, include a source of light, which usually has the form of a diode emitting a beam of light with complex parameters (inter alia the set length of the light wave), and a detector (usually a phototransistor). During the measurement the device illuminates the measurement chamber with a light impulse, while the detector registers the reflection from the particles. Basing on the information provided by the detector, it is possible to calculate the quantity of particles of an (approximately) assumed size, in a unit of air volume. Additional control over the measuring system, for example controlling the duration and intensity of the illumination, and also using various light sources, allow to achieve good quality results in a short time. Optical methods are used in portable devices (for example Protinus or DustTrack), thanks to the speed of the measurement and a low need for electricity.
Microbalance methods consist in gathering particles of a given size with properly selected filters. During the measurement, the resonating frequency of the filter’s vibrations is being assessed, which changes due to the increasing mass resulting from the gathering particulate matter. Then the change in frequency is being converted into particle mass. These methods allow to carry out measurements in short intervals, however their accuracy depends on many factors such as the resolution of the resonating measurement frequency, humidity, temperature, and other.
Automatic method, equivalent to the referential – in this case, various automatic measures are being used. These measures constantly collect data concerning the concentration of the particulate matter, which allows to present the result “on-line” on environmental protection websites (GIOŚ and WIOŚ), and in the GIOŚ app “Jakość powietrza w Polsce”. The data is being updated each hour in order to be compared with the acceptable levels and converted into the daily value.
This data is regarded as “raw”, meaning such which did not undergo any verification.