FI101504B - Method for the quantitative determination of elements for the detection of air pollution in the vicinity of the source - Google Patents

Description

101504

The present invention relates to a method for the quantitative determination of air pollutants in the vicinity of an emission source. The present invention relates to a method for the quantitative determination of air pollutants in the vicinity of an emission source.

Despite the rapid technological development of environmental protection and the clear reduction of many emissions, the need to study the spread of air pollution 10 is constantly growing. New industrial activities bring new problems. The need to increase knowledge of the state of the environment and reduce emissions is also growing.

In the field of air protection, methods for spreading emissions are not yet very advanced and are partly controversial and subject to subjective factors 15. Therefore, there is a need to develop very precise methods and there is a demand for such methods. They are needed by production facilities, which need to be better informed about the spread of their own emissions as legislation tightens and to ensure the marketing of their products.

They need accurately measured and indisputable information. The authorities that monitor the state of the environment are often 20 clients of research.

The spread of air pollution has previously been studied e.g. using many standard methods (SFS 5669, SFS 5781, SFS 5782, SFS 5783: determination of the sulfur content of conifer needles by different methods; SFS 5670: lichen mapping; SFS 25 5671: chemical analysis of mosses; SFS 5672: fluoride content of conifer needles; SFS 5794: moss; . The surfaces of pine needles have also been examined using a scanning electron microscope (SEM), in which case the contaminant particles on the surface have been specifically studied. The elemental composition of these particles has been previously studied using an energy dispersive 30 X-ray microanalyzer (EDX) (Meinander, Finnish Meteorological Institute, Air Quality Department, final report to the Ministry of the Environment, 30 p., Helsinki 1993, Juhanoja & Meinander, Extended abstracts of the 46th Annual Meeting Microscopy, 1994). However, these studies were limited to 2,101,504 particles larger than 2 μΐη in diameter. EDX has also been used to measure seasonal variations in Mg and S on the surface of Ramalina duriae algae as percentages of the 12 elements analyzed (Garty et al., Arch. Environ. Contain. Toxicol. 24, 455-460 (1993)). However, this method is not useful for many environmental studies because it provides information only on the relative proportions of the elements in the sample, but not on their absolute amounts.

The object of the present invention was to develop a method which would allow the quantification of contaminants, including those which are not detectable in the normal SEM range, i.e. also the non-particulate concentration. The method provides a much more accurate picture of the distribution of the substances studied. Based on the results of the method according to the invention, it is possible to obtain better information on, for example, the relative proportions of the local emission source and emissions from elsewhere. The method according to the invention finds air pollutants which cannot be properly measured by examining, for example, the total concentrations of needles or bark or the soil, because the air pollution to be examined in these other methods is only a small part of the total mass. The invention also enables the retrospective determination of past emissions, and in monitoring studies e.g. in connection with air protection measures.

20

The invention thus relates to a method for quantifying elements for determining the spread of air pollutants in the vicinity of a source, the method comprising the steps of: collecting a sample of vegetation surrounding the source by sampling the concentrations of elements accumulated on the surface of the sample are measured with an energy dispersive X-ray microanalyzer (EDX) connected to a scanning electron microscope (SEM).

3 101504

According to a preferred embodiment of the invention, the concentrations of the elements are determined per area of the sample using standard preparations of said elements, in particular a standard curve based on corresponding measurements of the standard, to which the analytical results obtained by SEM / EDX are compared.

5

In the method according to the invention, the sample is thus taken from the vegetation surrounding the emission source, in particular wood, from its surface part. A sample taken from the surface of wood, especially pine bark or needles, or from lichens growing on bark, is particularly suitable as a natural sample material.

10

According to a preferred embodiment of the invention, samples are collected from sampling sites located on a research line extending away from the emission source. Several, even tens of, samples are taken from each sampling site, with a few replicates being taken from each sample to increase the reliability of the method. The samples are preferably taken on a test line extending away from the emission source in an air direction corresponding to the prevailing wind direction. Preferably, the terrain between the sampling point and the emission source is as unobstructed as possible, i.e. it should not contain trees that impede the free flow of air pollutants, or other topographical obstacles.

20

According to the invention, a plot of the average sample concentrations measured at each sampling site as a function of the sampling site distance from the emission source is prepared. The regression equation corresponding to this plot and the corresponding explanatory degree (correlation coefficient) can be used to interpret the propagation of air pollutants on the studied line. In particular, they can be used to determine the relative proportions of emissions from a local source and elsewhere.

The method according to the invention thus comprises four main steps, namely - sampling - preparation of samples - microscopy of samples - measurement of samples.

4 101504 1. Sampling

According to the most preferred embodiment of the invention, the sampling is performed at the sampling site of the research line as follows. Samples are taken from a tree, such as a pine trunk, from a suitable height, eg about 1.5-2 m, on the source side.

5 The terrain between the sample tree and the plant should be as unobstructed as possible, ie no terrain obstacles, trees, etc. Pine trees aged 60-80 with similar conditions should be chosen as the sample trees from similar conditions. At each sampling site, a few trees are sampled with a knife, each with a few centimeters in size. The samples may be thin, eg 0.5-3 mm. The samples are dried, for example in paper bags, for at least a week at room temperature, protected from dust.

2. Sample Preparation SEM samples should not be handled with bare hands, as dirt and dust coming off the skin will easily contaminate both the sample and the microscope. Thus, either tweezers or plastic gloves are preferably used to handle the samples. The samples are preferably prepared as follows. Double-sided tape is attached to the metal sample trays. Take four pieces of approximately 1 cm2 from each sample on one sample tray with a preparation knife. The pieces are carefully attached to the tape with tweezers.

20 Samples are stored in petri dishes.

If an attempt is made to examine a biological sample as such by SEM, the sample will rapidly charge as the electron beam wipes its surface and imaging will be inhibited. In order to discharge the charges from the sample, its surface must be made electrically conductive. This is done by evaporating on the surface of the sample a thin layer of an electrically conductive substance, e.g. carbon, or especially a gold-palladium alloy, which is a good conductor. Evaporation can take place in a vacuum evaporator known per se, i.e. a so-called by means of a sputtering device. Gas ions (argon) bombard the gold source, releasing gold atoms from it. The resulting "gold atomic cloud" forms a uniform, thin layer of gold on the surface of the sample. Finished sputtered samples can be stored in a petri dish for about a week.

5 101504 3. Microscopy of samples by SEM

A tungsten filament is used as the electron source or cannon, from which the detached electrons are accelerated in an electric field and the electron beam is focused (aligned) with magnetic lenses on the surface of the sample so that the diameter of the jet is as small as possible. Apertures placed in connection with the lenses are used here. Under the influence of the electron beam, several signals indicating its properties are obtained from the sample, including the X-rays to be analyzed in the X-ray microanalysis.

In SEM, the easy and fast sample preparation technique allows the analysis of a large sample size of 10 and the interpretation of the results with the help of statistical tests.

In this work, SEM is used for the general examination of samples and for the selection of measurement targets. The actual measurement is performed with an SEMr-connected X-ray micro-15 roan analyzer.

4. Measurement with an X-ray microanalyzer X-ray microanalysis is based on the irradiation of an investigated material with an accelerated electron beam, releasing electrons from the inner shell of atoms 20 (K). They are replaced by electrons from the outer shell (L or M). Because the electrons in the outer shell have a higher energy than the K-shell, some of the energy of the electron transferred from the L-shell or M-shell is converted to X-rays, the energy of which depends on the orbital (electron circle) change that has taken place. This change and the energy it generates is “species-specific” for each element.

25

A detector (detector) is installed in the chamber of the electron microscope, which calculates the amount of X-rays detected at each energy level. It is represented graphically so that the radiation emitted by each element appears as a peak in question. at the spectral position characteristic of the element. The height of the peak may be used (taking into account other factors) as a measure of the amount of that element in the sample.

The analysis can be performed on a very small object, where up to 10 * 17 g 6 101504 elements are detected. The height of the spectral peak of each element is read using a scale attached to the monitor. A calculation program (eg Excel 5.0) is used to present the results. The averages for each sample site are reported for each element as a function of the factory calculated distance (XY) scatter plot. Using a program, a trend line is drawn for Scheme 5, for which a 3rd degree polynomial is most commonly applied, as well as a regression equation and a degree of salinity. These can be used to interpret the spread of these air pollutants along the line studied. If necessary, the statistical significance of the differences between the different sample points is tested by analysis of variance (e.g. with Statistix).

10 The following example illustrates the invention.

Example

The applicability of the method has been tested in the environment of three different emission sources. The plants that make up the respective emission source can be described as follows: 15 1. A medium-sized Finnish industrial plant that has caused significant pollution of the surrounding environment with its air pollution. In this context, attention has been paid mainly to the plant's alkaline dust emissions. The test study extends 1.3 km from the facility. In this area, the significance of other installations as well as long-distance transport for most emissions is non-existent or insignificant.

2. A relatively large Finnish metal industry plant that has caused pollution of the surrounding environment with its emissions. The study extends 3 km from the plant and in this area the the plant is an almost exclusive source of emissions for the 25 substances studied.

3. A large industrial complex in a neighboring country that has widely polluted its environment. The study extends approximately 100 km from the facilities. There are several other institutions in the area that influence research results.

In all cases, the new method has given very good results, which have been comparable to previous studies with other methods.

30 7 101504

Object No. 1 is described in more detail below. Here, the concentrations of Al, Ca, Fe, K, Mg, S, and Si of the seven elements in the pine bark were studied. The sample sites, 6 pcs., Were located on a test line extending to the northeast (direction of the prevailing wind), at the following distances from the factory (sample site number in brackets) 150 (1), 290 (2), 360 (3), 490 5 (4), 980 (5 ) and 1300 m (6). The size of the samples was 10-40 cm2. Samples were taken on the southwest side of the trunk, i.e. on the most exposed side of the tree, at a height of about 1.5-2 m. The sample trees were selected from places where the terrain between the emission source was as unobstructed as possible. The presence and condition of epiphytic lichens and major algal species in the pine bark at each sample site as bioindicators of these sample sites were also studied.

The samples were air-dried in paper bags, then attached with double-sided tape to the surface of the substrate and coated with a gold-palladium mixture (80% / 20%, about 45 nm layer) using a JEOL Fine Coat Ion Sputter JFC-1100 coating machine. Gold 15 was used instead of carbon to achieve better contrast. Samples were examined with a JEOL JSM scanning electron microscope using a JEOL Semaphore imaging system at 15 kV. Analyzes were performed directly in SEM using a PGT Imix EDS microanalyzer. The voltage used in the energy dispersive analysis was 15 kV, and the X-ray collection time was 60 s. For each sample site-20 ka, 40 points were analyzed with four different sample samples (from two trees, two sample samples per tree, 10 points for each sample). A 3x magnification corresponding to a surface area of about 450 μχη2 was used for X-ray collection. At higher magnification, the role of individual particles became overemphasized while the measurement peaks in the analysis remained too small at lower magnification. However, it is clear that when using different materials and conditions, it is also possible to use a higher or lower magnification, such as 100-5000 times. The number of analysis points per sample site may also vary, e.g. between 10-100.

30 Calcium, magnesium, sulfur, silicon, aluminum, potassium and fluorine contents were measured as follows. The peak for each element was measured using a scale from 0 to 5, to the nearest quarter. In some cases, very high element concentrations of 8,101,504 caused the peak to extend beyond the scale, in which case the collection time was taken to be 40 s. The maximum value of the element concentration in these cases was 8 instead of 5.

5 Standard preparations were used to standardize and calibrate equipment and measurements. Preparations were made on plastic-based tape. Calcium acetate was dissolved in ethanol. 10 μl of 0.01, 0.02, 0.04 and 0.1% calcium acetate solutions, respectively, were pipetted onto the tape and freeze-dried. A 0.04% solution of calcium acetate was used to calibrate the equipment. A standard-10 trend line was calculated for the standard measurements, where the height of the element peak (y-axis) is a function of the element concentration (Eg / mm2, x-axis). The equation of this trend line was used to determine the concentration of element on the surface of the sample. Standards for other elements were prepared by a similar procedure.

15 Result-specific regression trends and corresponding regression equations and explanation rates were calculated using Microsoft Excel, version 5.0, and other statistical calculations using Statistix, version 4.1.

For the following elements, the following results were obtained: 20 Calcium

The amount of calcium on the surface of the pine bark in the vicinity of the emission source was very high and decreased rapidly with increasing distance, clearly measuring 600-700 m. The explanation rate of the regression curve was found to be 0.99, indicating that this emission source completely causes elevated levels of calcium on the study-25 line. Such a high level of explanation is very rarely achieved in bioindicator studies of this kind, and the result shows that this method gives a very accurate picture of the spread of calcium emissions. The degree of explanation can be calculated mathematically from the formula y = -9E-09x3 + 3E-05x2 - 0.023x + 7.0601 (or y = -910'9 x3 + 310'5 x2 - 0.023x + 7.0601) (Figure 1), where y = amount of calcium on the surface of the 30 bark of the pine and x = distance from the emission source. Calcium diffusion has been studied at the same site using previously known best methods. They have otherwise obtained similar results, but they have not been as precise. In this case, the total mass of pine needles and soil humus have been used as material, whereby the results of the analysis are influenced by many other factors related to the composition of the soil and needles in addition to the emission source in question. Explanation values have been obtained from needle studies at 0.46 and humus at 0.74. The values of 5 are thus decisively lower than in the method according to the invention, which is due to the fact that in the comparison methods the results are affected by many other factors.

Magnesium

The amount of magnesium in the pine bark gives very similar results as for 10 calcium. The explanation rate is 0.95, indicating a strong influence of the local emission source. Magnesium concentrations are much lower because the emissions are also low.

Sulfur 15 Sulfur concentrations have also clearly increased in the vicinity of the plant and are declining rapidly as the distance increases. The explanation is 0.83 (Figure 2). It can be concluded from this that the results are also affected by others other than the one in question. sulfur emissions from the mill: about 10 km away is Finland's largest source of sulfur emissions, in addition to which long-distance transport contributes to the sulfur concentrations in the bark surface. A comparison of the explanatory levels of sulfur and calcium can be used to estimate the relative proportions of that emission source and other sources. The generally accepted method, measuring the sulfur content of pine needles, has not found any elevated sulfur concentrations in the vicinity of this emission source. This is because the sulfur content of the needles is most affected by emissions as gaseous sulfur dioxide, and in this case, the sulfur comes as particulate calcium sulfate. Its sulfur can be detected and measured on the surface of both the bark and the needles by a new method.

Silicon, aluminum and potassium Concentrations of silicon, aluminum and potassium on the surface of the pine bark had also clearly improved near the emission source and decreased as a function of distance. The explanatory degrees were Si 0.95, Al 0.93, and K 0.99 (Figures 3 and 4) and showed that the local emission source has a very large effect on the elevation of concentrations. All 10,101,504 gave a clear rise in the third-order polynomial curve to the fifth sample point, where the concentrations were higher than in the fourth and sixth. The same was observed with calcium. This was because the Fifth Sampling Point in question was selected from the edge of a sandy parking lot for 3-4 cars next to a wooded highway, thus showing the effect of 5 minor sand dusts. This result also shows that the new method is very suitable for detecting the effects of even small sources.

Fluorine

In addition, the amount of fluoride was clearly measured from the pine bark, which was clearly elevated at sample-10 at point I and was also detected at the second sample point. The plant had had a single release of calcium fluoride dust caused by the storm 1.5 years before sampling, the effects of which could therefore still be seen in the pine bark. This and other studies show that the method is also well suited for monitoring studies of changes in emission levels and for studies in which it is possible to detect the spread of individual emissions into the environment afterwards.

PGT bulk sample analysis was also performed at the sampling line of the study line, using the ZAF method, to obtain the following relative proportions of the elements: 20% by weight of the element

Calcium 59.75

Pi 14.06

Aluminum 10.98

Magnesium 3.24 25 Fluorine 11.97

Claims (12)

1. A method for quantitatively determining elements to investigate the spread of air pollutants in the environment around an emission source, characterized by the following steps: of the sampling object facing the source of emission, - the sample is dried, - the surface of the sample is made electrically conductive, 25. the accumulated elemental content of the sample is measured with a tile electron scattering microscope (SEM) coupled energy dispersive X-ray analyzer V (EDX). Method according to claim 1, characterized in that for the determination of the levels of the elements per surface of the sample, standard preparations of the elements are used with which the measurement results obtained by SEM / EDX are compared. 101504 Method according to claim 1 or 2, characterized in that the sample has been taken from the surface of bark or conifer of trees, in particular of thalli. Method according to any of the preceding claims, characterized in that one or more of the elements Ca, S, Si, AI, Mg, K and F are measured. 5. A method according to any of the preceding claims, characterized in that the sample is made electrically conductive by coating it with gold. 10 Method according to any of the preceding claims, characterized in that a 100-5000 thread magnification is used to collect X-rays. Method according to any of the preceding claims, characterized in that for each test site 10-100 sample points are analyzed. 15 Method according to any of the preceding claims, characterized in that the samples are taken from test sites located on a research line that extends from the emission source, and from each test site several parallel samples are taken. 20 9. A method according to claim 8, characterized in that the line of research extends away from the source of the emission in the weather distance corresponding to the saving wind direction. Method according to claim 8 or 9, characterized in that a diagram 25 is prepared for the mean values of sample contents measured at each sample site as a function of the sample site's distance from the emission source, and this corresponding regression equation and correlation coefficient are used to interpret the spread of the air pollution on the line under investigation.