To determine the concentration of harmful substances, it is first necessary to take samples of atmospheric air. This process is extremely important and painstaking. This is due to the fact that even with the most accurate analysis, the results of improper air sampling are distorted. Therefore, there are a number of requirements for this process:
- it is necessary to obtain a sample that matches the actual composition of the air;
- accumulate in the sample the right amount of the desired substance, so that it can be detected in the laboratory.
Air sampling depends on several factors:
- the state of aggregation of the sought substance in the environment (condensation aerosol, gas, steam);
- possible chemical interactions of the desired substance with the surrounding atmosphere;
- amount of substances in the air;
- research method.
During research in the laboratory, various methods of sampling air are used. The most common are aspiration and vessel selection.
Suction method
This is the most common method in hygienic practice. A feature of this technique is aspiration. In other words, it is filtering the test air with the help of special substances that are capable of absorbing a certain ingredient from all passing through it. This substance is called an absorption medium. Disadvantages of the suction method for air sampling:
- This is a very time consuming process.
- It takes a lot of time (about 30 minutes). During this period, averaging of the concentration of the toxic substance may occur. And the concentration of the desired substances in the air changes too quickly. The air sampling technique is carried out by professionals.
Selection in vessels
This method is notable for its speed. It is used when it is limited to a small volume of the studied air and there is no need for the accumulation of the desired substance in the sample. In this selection, various containers and vessels are used: cylinders, bottles, syringes and gas pipettes, as well as rubber chambers. This air sampling technique is very sensitive and accurate.
In practice, several varieties of aspirators are used. The simplest among them is water. This air sampling device consists of a pair of identical glass bottles that are pre-calibrated. These vessels hold about 3-6 liters, are closed by stoppers, from which two glass tubes come out. One of them is long and reaches the bottom of the bottle, the other is short, ends immediately under the cork. Long tubes of a pair of bottles are connected by a rubber tube with a clamp. An absorber joins the short one. When the clamp opens, water enters an empty vessel located above the one in which the liquid was originally located. At this time, a rarefaction occurs above the surface of the water, due to which the air under investigation is sucked through the absorber. The rate at this suction is from 0.5 to 2 liters per minute, and the volume of air passing through the absorber is the same as the amount of water that went from the top bottle to the bottom.
This method is time consuming and one of the most difficult. Convenient for use is the Migunov electric aspirator. This device combined an electric blower with rheometers, which are glass tube-rotameters, two of which are needed for measuring the air sampling speed, and the other two are designed for high speed. Low speed is from 0.1 to 1 l / min, high - from one to 20 liters per minute. The lower part of the rotameters is connected to the fittings output to the front of the device. Rubber pipes are connected to these fittings together with absorption devices. Thanks to this scheme, four samples can be taken simultaneously. The upper part of the rotameter has valve handles, which are likewise brought to the front. This helps regulate the air sampling rate.
The principle of operation of this device is that during inclusion in the network using an electric motor rotates the rotor of the blower. At the same time, pressure drops in her body. And the air placed outside the device passes through the fittings. Then comes out. Having learned the time spent on its passage through the aspirator and its speed, you can determine the amount of air passing through the absorption device, which is attached to the fitting.
Existing absorbers are designed to remove chemical impurities from the air using solid and liquid media. Both the absorber and the environment for him are not chosen randomly. It takes into account the state of aggregation of substances that are being tested. And also the need to ensure continuous contact of the substance itself and the absorption medium.
If the test gas or vapor substance is in large quantities in the air, if the method for its determination is very sensitive, then, accordingly, small volumes of the analyzed air are necessary. For this, instant sampling methods are needed. They use rubber chambers, calibrated bottles and vessels containing from 1 to 5 liters, as well as gas pipettes of 100-500 ml. However, rubber chambers can only be used if the test substance does not exactly react with rubber. They do not retain air for more than three hours. He is pumped there with a bicycle pump. For research, air is transferred to a calibration bottle or other absorber with the appropriate medium.
Exchange Selection
When gas pipettes and bottles are filled with test air, this method is called the exchange method.
Laboratory air can be blown through a pipette or bottle many times. The pipette is filled with a rubber bulb, a pump. This is possible with open clamps or taps, if any. At the end of sampling, they close. In the case of using a calibration bottle, it is equipped with corks and two glass tubes. Rubber tubes with clamps are attached to their outer ends. Before selection, the clamps are removed. And to one of the tubes joins a pump or a rubber bulb. Then the bottle is purged with test air many times. At the end of sampling, the tubes are covered with clamps.
Vacuum method
Indoor air samples are taken with a thick-walled calibration bottle. It is needed to create a vacuum in it using a special Komovsky pump. The test air is sucked out of the bottle to a residual pressure that ranges from 10 to 15 mmHg. Then you need to close the clamp on the rubber tube. Disconnect the vessel from the pump. And at the end of the rubber tube insert a glass stick. At the sampling location, the container opens. It will quickly fill with air due to equal pressure. At the end of sampling, the clamp is screwed, and a glass stick is put in place of the holes of the rubber tube.
Pouring method
Air sampling is carried out using a gas pipette or calibration bottle. They are filled with a special liquid, which should not react with the test substance and, moreover, dissolve it. Simple water is often used for these purposes. In cases where this option is excluded, resort to the use of saturated (hypertonic) solutions of sodium or calcium chloride.
At the place of sampling, the liquid is poured out, and the vessel is filled with the test air. Then the rubber tubes are closed with special clamps, and glass poles are placed at the ends, or they simply close both valves on a gas pipette.
Sanitary samples
These samples are collected for chemical analysis and determine the total dust content in the human breathing zone and one and a half meters higher.
Studying air pollution due to emissions from industrial enterprises, determine the average daily and maximum one-time concentration of harmful substances in the atmosphere. Sanitary air samples are usually taken at the time of greatest pollution from the windy side of the source. A minimum of ten samples are taken at all points and at regular intervals. Sampling of atmospheric air lasts about twenty minutes. With increasing distance from the source from which pollution originates (no more than five kilometers, further accurate analysis is simply impossible), the duration also increases to 40 minutes.
In order to determine radioactive and carcinogenic substances, a large volume of air must be sucked through the filters. Because in populated areas the studied elements are contained in a negligible amount. In the process of taking air samples in large industrial enterprises for the study of the content of toxic substances (such as gases, vapors) or a large amount of dust, an important place is taken by the sampling point. Pollutants are not evenly distributed in production facilities or buildings. The air environment is constantly and randomly mobile. For these reasons, instruments for atmospheric sampling are located in the place where the working process takes place, at the level of one and a half meters from the floor. This is considered the breathing rate of the workers. Three samples are taken per shift: at the beginning, middle, and end of the working day. During their capture, humidity and the temperature of the room must be taken into account. Absorption devices, which are needed to take air samples at industrial enterprises, resemble glass tubes, which are sealed at the top and fastened with a couple of glass tubes. The test air enters through a long tube. And through a short one he goes further to the blower through a rheometer. The lower part of the absorber is designed for absorbed liquid through which the test gas must be sucked. Sampling of the air of the working area is necessary for the normal functioning of the enterprise and ensuring working conditions for the team. In accordance with applicable law and labor protection requirements, this is a mandatory process.
Gravity selection method
This method of taking air samples indoors or outdoors is based on the fact that the dense particles that are weighed in it settle under the influence of gravity. The Durham sampler is the main instrument used for gravity sampling of the air. The essence of his work is as follows. A special glass slide is inserted into the device holder, which is coated with glycerin gel. Then it is left in the air for a day. Particles that are carried by air flow settle on a glass slide. Further, in laboratory conditions, under a microscope, the composition and number of particles are determined. The results are represented by the number of particles settled per square centimeter per day. The gravitational method of sampling air is inexpensive and quite simple, however, it also has its drawbacks:
- analysis results may be inaccurate due to factors such as direction, wind speed, precipitation, and air humidity;
- a small amount of particles manages to settle per day;
- coarse particles fall on the glass slide;
- Samples are collected by professionals, for this they need special devices, as well as aspirators for sampling air.
Volumetric method
The essence of this method lies in the fact that particles that are weighed in air are delayed by obstacles set by its flows. Samples of air in heavy industry enterprises should be collected at least once a year. In the conditions of this method, the following intakes are used:
- Rotary. Its collecting surface is covered with a special substance, then it rotates for a certain time at the right speed. The result of the test using this device is expressed by the number of particles that have time to settle per day on one square centimeter. This method eliminates the influence of the direction and speed of the wind on the result of the analysis, thereby giving a more accurate analysis. The Academy of Allergologists and Immunologists recommends using such a device to find harmful substances in the air.
- An aspiration probe can pass test air through a membrane filter with a given pore diameter. The collecting surface is needed so that particles of a certain size settle on it. This principle is key to Bukhard's spore trap, where the collecting surface can move at a speed of about 2 millimeters per hour. This makes it possible to monitor how the concentration of particles in the studied air changes. The device has a weather vane, and therefore the direction of the wind does not affect the final results.
Assessing the results of the gravitational selection method allows you to detect large particles (for example, ragweed pollen). For scientific purposes, more powerful and accurate volumetric methods are used.
Pollution studies
In accordance with applicable law, air sampling takes place. GOST 17.2.3.01-86 is necessary for the correct analysis and calculation of errors.
In order to study the degree of air pollution in the Russian Federation, they developed a special term - "maximum permissible concentration". To date, the maximum permissible standards have been determined. The concentration in the air of harmful substances should be no more than five hundred substances. Air samples allow you to control the situation.
The most admissible is considered the most concentrated admixture of atmospheric air, which refers to a certain period of time and periodically or throughout a person’s life will not have a harmful effect on him (long-term consequences are taken into account) or on the environment.
In the case of a high concentration of gases, air breakdown is carried out, the voltage in this case is about 33 kV / cm. With increasing pressure, the voltage also increases.
There are laboratories, research institutes and individual qualified specialists who, using modern instruments and high-tech devices, identify and eliminate harmful substances in homes, apartments, offices, land plots, etc. Air sampling is carried out by sanitary and epidemiological workers, and then they are tested in laboratory conditions.
How to secure your home
If you began to notice that someone from your family members (or yourself) suffers from allergic reactions for unknown and invisible reasons, then you need to analyze indoor air samples. There are several ways to do this. Ordinary dust, mold, radon or various pathogens in the air negatively affect the health of people, especially young children. Sampling of atmospheric air is necessary in case of allergic and other reactions in one of the family members. Methods to help analyze indoor air:
- You must install a carbon monoxide detector. This device plays an important role and, without exaggeration, saves lives. To install this small device, you only need a power outlet. If the sensor emits a warning sound, it means that the level of carbon monoxide has changed in the apartment . As you know, gas has no color and almost no smell, but because the role of the sensor is really very large, it can save your life.
- Another way to protect your home is to analyze the air in the room for radon. This is especially useful if the house is located near the site of uranium concentration in the ground, which can lead to the accumulation of radon. Air samples in the apartment in this case must be carried out regularly. There are kits designed for chemical analysis for the content of radon in the atmosphere. They can be used independently. Install and leave them for three days. After that, the kit is assembled and taken to the laboratory for examination and verdict.
- You can also buy mold spore test kits. To determine if there is fungus or mold in the apartment, it is necessary to conduct a microbiological analysis of the air. Usually this method is resorted to if someone in the family suffers from allergies or sinusitis. You can use the instruments for analysis yourself. However, to get the results, you still have to use the services of a laboratory.
- At home, you can check for dust mites in the air . This phenomenon is present in almost all houses, especially private, close to planting and forests. However, if the concentration of ticks, bugs, fleas is too high, it is almost the same as toxic air. For laboratory analysis, a small bubble is issued in which an air sample is placed, and then sent to the laboratory for analysis and obtaining results.
After receiving the results, it is necessary to solve the corresponding problems. To eliminate them, there are special groups of people who work on a call.