Indoor air pollution
Kategorie: Biológia (celkem: 966 referátů a seminárek)
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- Přidal/a: anonymous
- Datum přidání: 07. dubna 2007
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Indoor air pollution
INTRODUCTIONNumerous scientific studies show that indoor of homes and businesses are the source of potentially harmful substances called indoor air pollutants. They come from variety of sources. Indoor levels are often much higher than outdoor levels and most people spend the bulk of their lives indoors. This is the biggest single contributor to health-damaging indoor air pollution in cities. Regulation of fumes emited by vehicles and factories has something to offer by way of solution, but what is needed most is increased health by better housing and by proper planning of cities and roads. The problem cannot be solved simply by academic laboratory research. An air pollutant is seldom present in outdoor air on its own and normally the air contains a mixture of several pollutants. The composition varies according to the prerequisites. It has not yet been determined how the various substances affect human beings when they interact. Main groups of pollutants were subjects of our special interest as nitrogen oxides, volatile organic compounds, carbon monoxide and sulphur dioxide.
INDOOR CHEMICAL POLLUTANTS
Nitrogen Oxides
Nitrogen monoxide and nitrogen dioxide are mainly produced by combustion at high temperatures and are formed by reactions between nitrogen and oxygen. Both nitrogen in the fuel and nitrogen in the air participate in reaction, NO is further oxidized and transferred into NO2 in the atmosphere. Nitrogen dioxide is the most toxic of the nitrogen oxides and is the most important from view-point of health. In Slovakia it is possible to assess that about 40 % of nitrogen oxides emissions originates from road traffic, about 50 % from combustion and about 10 % comes from industrial processes. During recent several years the emissions of nitrogen oxides have increased. There is great difference between annual average value of nitrogen oxides in the countryside and in the big cities. Outdoor average concentration level of nitrogen oxides are shown in figure 1. Nitrogen oxides are also formed during lightning storms and are said to be responsible for part of the continual increase in acidity of rainfall.
Figure 1: NOx concentration level dependences
People are mainly exposed to indoor nitrogen oxides. Indoor air can be contaminated by the use of gas for heating and cooking appliances. The most important indoor source of nitrogen oxides is gas burning in the kitchen.
The other reason of increasing indoor exposure level is environmental tobacco smoke. Compared with sulfur dioxide, nitrogen dioxide has a much lower water solubility, therefore it penetrates deep into the air passages more easily. Finally concerning the indoor environment, indoor air can be contaminated by using gas for heating and cooking and this probably involves a certain health hazard.
The research results show that seasonal differences of indoor exposure level exist there. As continual measurements were done and average monthly values were established for indoor and outdoor environment, these dependencies are shown in figure 1. The average indoor concentration of nitrogen oxides has been found to be higher by approximately 24 µg.m-3 than that outdoor, which has been measured at about 45 µg.m-3 .
The measurements have been done in apartments with gas ranges. Indoor NOx exposure level is much higher in winter time. There are considerable differences between the measured concentrations in various apartments owing to different ventilation levels and gas burning activities, which make the estimation of exposure and the corresponding health risk assessment very difficult.
Average long time values of indoor level exposure are mostly lower than allowed long time standard concentrations. The problem becomes serious in short time NOx exposure. A lot of measurements were done in order to describe situation of indoor nitrogen oxides concentration level after cooking. The values increased so rapidly that it was necessary to open the windows several times. The comprehensive analysis of indoor and outdoor air nitrogen oxides pollution in Slovakia shows that extent of indoor air level exposure varies with the different meteorological conditions, seasonal changes, ventilation level and indoor burning activities. On the whole, in winter months the indoor air quality is worse. In summer the indoor exposure concentration of nitrogen oxides were basically at the same pollution level. This indicated that indoor and outdoor air qualities are similar in summer. It also demonstrated that indoor and outdoor air qualities are usually worse in wintertime than in summer. Both burning and smoking in the rooms have similar risk as major pollutant factors including respiratory illnesses, allergic symptoms and lung cancer. Therefore prevention and research of gaseous pollutants and their impact on health must be put on the same level as prevention and control of other types of pollutants.
Reducing indoor burning processes and smoking are important measures to prevent sick building syndrome.
Volatile Organic Compounds
Volatile organic compounds are now a major source of air pollution in Europe. They are as much a part of the air we breathe as oxygen, nitrogen and carbon dioxide. Indoors, a VOC has been defined as any organic substance that can release vapor to the atmosphere with the potential of causing effects at low concentration. The United Nations Economic Commission for Europe, considering the outdoors has said that VOCs are all organic compounds of anthropogenic nature other than methane that are capable of producing photochemical oxidants by reactions with nitrogen oxides in the presence of sunlight. Among the apparently limitless number of organic chemical compounds that exist there, is a large number that is commonly found in the built environment. They are there either because we put them there, for example emissions from vehicles and number of solvents we use, or are present incidentally as a component of something else such as plasticisers and natural products like pinene in wood.
Outdoor air, exactly emissions from vehicle exhausts are the major source of VOCs in urban life in Europe. There has been a qualitative change in environmental VOCs in recent years as vehicle fuels have changed dramatically with the introduction of unleaded petrol.
Sources of VOCs in indoor air are numerous and can be summarized as follows: building materials, solvents and adhesives, environmental tobacco smoke, cooking and outdoor sources.
Since by definition VOCs are present in the air, the only effective route into the body is by inhalation, although a number of compounds are absorbed through the skin. This is a less effective route and the only that is one for all practical purposes insignificant. The health risks associated with exposure to VOCs can be divided into four main categories: acute effects, carcinogenicity, neurobehavioral effects and nephrotoxic effects. Emission of formaldehyde depends on finishing of surfaces, as the used material plays a primary role in formaldehyde emission. We certificate products with emission not exceeding 60 g.m-3. Certified materials were: particleboards, boards based on wood, wall-papers, carpets, textile floor coverings and related products. Concentration of formaldehyde emitted from 10 material samples fluctuates in between 16 - 100 g.m-3 , see figure 2.
Figure 2.
Formaldehyde concentration
Indoors, where larger surface is covered with such materials, formaldehyde concentrations can reach much higher levels.
Measurements provided by our research group in buildings constructed from particle board and wood panels show that the levels of formaldehyde exceed in many cases the given standard. The concentration is, yet strengthened by equipment - furniture, carpets, textiles, etc.
The majority of formaldehyde measurements in the indoor environment was performed in primary and nursery schools and in boarding centers, where the use of risk wooden material is abundant. Measurements in the working environment and lodgings represent only a small portion of the whole.
The primary sources of measured indoor formaldehyde concentrations in the indoor environment were: wood panelling, the construction of the walls, supplementary thermal insulation, containing phenolformaldehyde adhesive, supplementary acoustic insulation implemented mostly at music schools. The results of indoor formaldehyde concentration short term measurements are presented in the table 1.
Table 1.Short-term indoor formaldehyde concentrations
Source
of HCHO Concentration range
[g.m-3] Average concentration [g.m-3]
wood panelling 0,0 - 167,5 32,5
thermal insulation 16,5 - 105,0 51,6
acoustic insulation 0,0 - 216,6 74,3
On the other side, the results of long-term measurements of indoor formaldehyde concentration are in the table 2.
Table 2: Long-term indoor formaldehyde concentrations
Source
of HCHO Concentration range [g.m-3] Average concentration [g.m-3]
wood panelling 3,0 - 40,8 10,4
thermal insulation 11,2 - 79,1 24,5
acoustic insulation 0,0 -147,9 45,9
Recent studies show that a lot of inhabitants are exposed to high levels of formaldehyde and other VOCs. It´s essential to know where they primary come from and try to avoid their usage in the indoor environment. Another way how to address indoor air pollutants would be to develop reasonable indoor air standards, all comprising technical, economic and legal questions. Still, more research is needed to find out how indoor air pollutants affect our health. Creative solutions of the engineers and designers can, in the large scale, reduce exposure to the potentially harmful substances.
Carbon Monoxide
The primary sources of carbon monoxide indoors are combustion gases from vehicles and tobacco smoke. Opened fires indoors can generate high contents. Carbon monoxide is also spread from garages. Normal, fresh outdoor air contains about 2 mg.m-3 of carbon monoxide. In busy streets the content is about 10 mg.m-3. Smoking in a room may increase the content by 5-10 mg.m-3.
If the source is known, carbon monoxide can be used as an indicator of several pollutants in particulate and gaseous form from this source.
As the fuel burns, carbon monoxide enters the room air, binds to blood hemoglobin and reduces the oxygen - carrying capacity of the blood, an effect especially harmful to individuals with heart and lung diseases. Our study showed that the average particulate level is 40 mg.m-3 in home without smokers. Smokers raised particulate levels in some cases over ten times and it is level not allowed by air quality standards. Concentrations of indoor air CO pollutants fall after combustion sources are turned off, of course, but it may take several hours before normal levels are reached in conventional, poorly sealed homes. In well - sealed, energy efficient homes it could take much longer. If several lengthy meals are cooked during a day, exposure to these pollutants can be quite high. Typical situation when carbon monoxide level drops after the stove is turned off is in figure 3. As it can be seen, the concentration level in the kitchen is similar to the other rooms in the same flat. Concentration levels are trapped in various spaces of the flat also for the reason that the flat area is small.
Figure 3. Drop in carbon monoxide level in homes after the stove is turned off
Sulfur Dioxide
At present time, sulfur dioxide is not the significant indoor chemical pollutant but still has it's important position from outdoor air quality point of view. Outdoor sulfur dioxide pollution level is low and annual average concentrations in individual locations fluctuates within the range of 8 - 27 µg.m-3. Sulphur dioxide pollution is of seasonal course, reaching the maximum concentrations in winter. Regarding the prevailing wind directions, the industrial center of East Slovakia - Kosice, which results are presented, is favourably situated to the major sulphur dioxide emission sources. Sulfur dioxide concentrations were considerably lower as compared with those in the previous year. Under the air circulation, occurring in less than 5 % of cases within a year, the average sulphur dioxide concentration of about 50 µg.m-3 was achieved. In the whole, sulfur dioxide air pollution level ranged far below the ambient air quality standards. Our interest has been concentrated also to indoor concentrations of SO2 and its outdoor dependencies which are shown in the figure 4. The indoor level concentrations of sulphur dioxide change within the range of 5 - 17 g.m-3. Indoor sulfur oxides are comparatively rapidly decreased by so called “wall effect“, they are absorbed by lime plaster and their concentration goes down fast even if the room is ventilated by infiltration only. The concentration of sulfur dioxide is difficult to measure by one hour after closing the windows.
After opening the windows the concentration is balanced with the outdoor one.
Figure 4. The average daily concentrations of SO2
CONCLUSION
The problem building syndrome is significantly related to the total concentration of indoor chemical constituent. Indoor climate problems are more common in building construction environment without mechanical ventilation. It is evident that there is need to increase the outdoor air supply in the indoor of buildings, to minimize the exposure of indoor pollutants that might induce symptoms compatible with sick building syndrome. Furthermore, building materials, building constructions and indoor acitivities should be selected on the principle that the level of indoor air should be of the best quality or the concentration of negative agens should be as low as reasonably achievable. Creative approaches of civil engineers and designers can in the large scale influence indoor air quality.