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The Air in Prachatice |
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The evaluation of the state of the air in Prachatice
In the last years the state of the air in Prachatice has met with a considerable improvement in comparison with the previous years.
Especially with the continuous gas installation the concentrations of sulphur dioxide,carbon monoxide and floating powder has conspicuously fallen down.It is also confirmed by the indexes of the quality of the air where you can see the considerable trend of the gradual rising of the number of the days with the clear air.The state of the air from the point of view of the concentrations of nitrogene oxide is a bit worse because it is negatively influenced by the considerable grow of the car traffic in the last years. But in spite of this the highest permitted concentrations are overpassed only rarely,only several days in a year during the tempereture inversions where the location of the town in the valley is presented in a disadvantage way.
Next it was found by the long-termed measurement that especially during the imperfect combustion of solid fuel the air is emitted by quite considerable quantity of polycyclic flavouring extracts dangerous especially by their carcinogenic affect and by their persistation caused by their linkage on a fine powdered fraction.Even in the future the occurrence of polyaromatics in the natural cycle will keep on playing an important role and that's why the limitation of this kind of heating in the town Prachatice is an outstanding act from the point of view of the quality of the air.
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The sources of the atmosphere pollution |
The burning-up sources – heating plants and boiler houses of the plants |
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In the first place the local combustion chambres, and in a lower degree the heating plants and boiler houses of the plants, belog to the main sources of the pollution.The bigger firms,as for example Jitona Prachatice, used as a heating medium the North Bohemia sorted brown coal nut (the content of sulphur about 1,0 hm.%). But gradually during 90s in the town the number of the boilers was reduced and it was succedded by the transition on using the natural gas.At present the hard coal (with the content of sulphur about 0,3 hm.%) is burnt up only in a small number of smaller plants and so its "contribution" to the global pollution isn't outstanding.Since 1990 the gradual gas installation in households of the district town has been passing and at present the majority of the town area has been gas installed.
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The burning-up sources – the local combustion chambres |
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In local combustion chambres using the coal, namely especially in a temporary period, the imperfect combustion occurs.The combustion chambres are not equipped with any separating device and the chimneys are so low they don’t make any scattering of escaping harmful substances possible.It's also necessary to realize that in these combustion chambres the uncontrolled combustion of various waste including plastics is beeing done.These are the reasons leading to the fact these local combustion chambres participate in an important way in the air pollution not only by traditional harmful substances as sulphur oxides and nitrogene oxides,but also by powder to which other harmful substances including metal are bonded and by organic substances including carcinogenic polycyclic aromatic hydrocarbons.
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The burning-up sources – the mobile sources |
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Another important source of the atmosphere pollution is also all the time increasing car traffic participating mainly in nitrogene oxides emision.
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The Measurement of the Quality of the Air |
The history of the measurement |
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If we are talking about the measurement of harmful substances in the air of the Bohemian Forest district town Prachatice and about the following the development of its quality,it's necessary to mention so called "Programme Teplice" which was virtually the initiator of the systematic monitoring since the beginning of 90s of the last century.This project sponsored by the Ministery of the Environment of the Czech Republic was making an extensive task of investigation whose aim was to do a complex investigation into the influence of the environment on the health of the inhabitants in the basin districts of Northern Bohemia.The task started in 1991 set itself a goal to materialize the causes of the unsatisfactory state of the environment and its consequences on the health of the inhabitants,to suggest the priorities of the arrangements which would lead to the improvement of the environment and to verify their effectiveness.The distric Teplice was chosen as a model and the district Prachatice was chosen as a comparative one for the expected favourable parameters of the environment (especially of the air).
The measurement of the single pollutants in the air originated in 1991 when the withdrawal device VAPS was placed in Prachatice and thanks to it it was possible to follow the occurrence of various substances from sulphur dioxide and powdered fractions via acid components of the air (HCl,HF,forms of the nitrous acid) and polycyclic aromatic hydrocarbons to the whole scale of heavy metals.Later on in 1995 for the more complex monitoring of the quality of the air on the withdrawal place called "Skalka" in Šeřík Street there was placed the automatic imission monitoring station belonging to the withdrawal system CHMU AIM.The withdrawal place was chosen by the specialist of CHMU in the way the imission concentrations of pulluting substances measured here represented some average concentration over the whole Prachatice hollow.
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Monitoring Station |
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In the station there are continuously monitored SO2, NO, NO2, NOx, CO, O3 O3 and the powder fraction PM10.Then of these measurements 30 minute averages are recorded and they are daily sent with the help of the modem to the branch of CHMU Plzeň where all the datas are verified,recorded and then presented on web pages of CHMU.The integrating datas are the continuous measurement of the temperature 2 and 10 metres above the ground,of the atmospheric pressure,of the relative humidity,of the wind speed and the wind direction and of the global solar radiation.
In the course of the years of all these measurements there exist quite large data sequences serving on the one hand as the basis for other studies within the framework of the project and on the other hand in this way it's possible to follow the development of the quality of the air itself in the district town.
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The results of the measurement
As to the cocrete situation concerning the quality of the air in Prachatice,the found information can be summarized into the following points:
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The course of the concentration of harmful substances during the day |
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If we follow the course of the concentrations of harmful substances during the day (Pict.7 and 8),we can see the higher concentration, as in a typical winter day as in a summer day,practically refer to the period of so called morning and afternoon "rush hours",when in the town we can clearly see the bigger movement of the persons,heavier traffic and other activities.
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The concentration of nitrogene oxides |
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By the nearer look at the daily course of the concentrations of NO, NO2 and NOx we can confirm the presumption the form NO is produced as the primary one during the combustion processes.Then the concentration of the form NO2 (it originates as the secondary one of the form NO by oxidizing processes,mainly with the help of the ground ozone) is going up with the heavier traffic in the period of the "rush hours" and with the increasing concentration of O3 in the time of strong solar radiation during the day.The form NO has the upper hand only early in the morning when it doesn't come about its oxidation yet.Both the highest admissible half an hour concentration and the highest average daily concentration are overpassed only in a several few days in a year.In Prachatice this is practically the only case when the overpassing of admissible limits actually happens.
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The concentration of SO2 |
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In January 1998 the average half an hour and day concentrations of SO2 are even in the "worst" days roughly fifth in comparison with the admissible limits of Ihk and Ihd.
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Ground ozone |
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Compared to other harmful substances the concentrations of the ground ozone are on the contrary going up in summer period in connection with the longer and higher solar radiation.But the highest recommended one hour concentration isn't overpassed.
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The comparison of SO2 and NOx |
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The graf of average month concentrations of SO2in the course of the years 1991 to 2002 shows the grows in winter months ( heating season) and in contradistinction to NOx it has a falling down trend illustrated in a graphic way by the spaced statistically found connecting line of the trend,which actually corresponds to the gradual gas installation in the town and thus to the decreasing of the combustion of solid fuels containing sulphur.
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The concentration of CO |
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The concentrations of CO originating mainly during the imperfect burning up processes have a slowly falling down trend,and the concentrations of ground ozone producing mainly in forest in oxygen rich localities by the influence of solar radiation have practically the persisting trend.
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The powdered fractions and PAU |
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The concentration of powdered fractions (PM) is measured synchronously with the help of two different devices working on different principles (AIM - ß - powdermeter, VAPS - gravimeter).Again the grow of the concentrations of PM2.5 (fine fraction) and PM10 (rough fraction) is recorded in winter period and the continuous falling down trend is recorded in the course of the years (likewise the effect of the gas installation).
The similar trend is also recorded with the average month concentrations of PAU (polycyclic aromatic hydrocarbons) whose source is mainly the imperfect combustion of brown coal and wood and they are also emitted among the products of exhaust gas of the cars.The danger of these,recently nearly omnipresent harmful substances, is especially in the carcinogenic effect of some of them and their persistence.In the air of Prachatice there is about one quarter of the total amount of the carcinogenic PAU.
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The values of the average yearly concentrations of representative harmful substances |
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The index of the quality of the air |
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For the appreciation of the cleanness of the air in Prachatice we also used the day index of the quality of the air (Pict.22 and 23).This one is a certain mathematical expression of the degree of the cleanness of the air (with the corresponding verbal evaluation) as to the imission concentrations of recorded basic harmful substances.In this case it concerns sulphur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO) and floated powder (fraction PM10). January is chosen as the most unfavorable month in a long termed way from the point of view of imission concentrations of harmful substances and only in a several few days the clean air is slightly worsened to suitable.At present in July ,as in a typical summer period,the air is very clean and index 1 of the quality isn't nearly overpassed.Even this is the certain index of the usefulness of the gas installation in Prachatice.
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The comparison of the air in Prachatice and in Teplice |
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The comparison of the air in Prachatice with the air in a typical basin town Teplice is shown in Pict.24 and 25.In the course of the years the concentration of NO has been falling down and the concentration of NO2 (has been slowly going up (the ever-growing car traffic).For the better notion the comparison of both of the towns is also presented according to the average month concentration of NOx in a typical winter month with the other values measured all over the republic.
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