ELECTROMAGNETIC POLLUTION

Electromagnetic radiation consists of the waves of enery combining electical and magnetic fields. These include whole range of electromagnetic wave spectrum: from very long-wave radio waves at one end to X-rays and gamma rays at the other end of spectrum. Visible light falls in a very narrow wave band in the middle of the spectrum. Every iving and non-living object in nature is constantly being exposed to a natural background of electromagnetic radiation that comes from space as well is produced by radioactive elements in the Earth’s crust. A large proportion of the cosmic radiation coming from space is absorbed by the atmosphere and only a very small portion reaches the ground. However, there is no such filtering of radiation originating from the Earth itself. All living organisms are evolutionarily adapted to such natural radiations in their natural environments. In fact, animals and plants use electromagnetic radiation for a variety of their living activities e. g. communication, control and regulation of their various physiological, psychlogical and behavioural functions. Though essential for living organisms, exposure to excess such radiation beyond the naturally evolved tolerence limits causes various harmful effects in them. The effects of increased exposure to electromagnetic radiation on human, animal and plant bodies are now coming to light and are being increasingly studied.

In the present urban, domestic and working place environments, sources of electromagnetic radiations are increasing rapidly. Increasing radiations from sources like power lines, microwave, telecommunication, electrical appliances, radar, transmissions of radio and television etc. are causing the problem of increasing electromagnetic pollution of environment.

The electromagnetic radiation may be classified into two broad categories according to the frequency and their effects. First category includes relatively low-frequency radiation, from visible light wave band down through infra-red, microwave, radar, television and radio waves and constitutes non-ionizing radiation. Second category includes relatively high frequency gamma and X-rays and constitutes ionizing radiation. Exposure to excessive dose of both the types of radiations casuses various harmful effects on living organisms.

The effects of extremely low-frequency electromagnetic radiations are dependent on dose and duration of exposure and are cummulative. It may take years of exposure before symptoms will appear. Usually symptoms of such electromagnetic pollution manifest as constant headaches, lack of energy, loss of apetite, mental blocks, decreased ability to concentrated, insonia & sleep disturbances, palpitaions, dizziness, trembling and rashes. After prolonged exposure, the symptoms may proceed to blackouts, nervous & psychological disorders like depression, feeling of being trapped, anxiety attacks, increased suicidal impulses, epilepsy, lowered libido & fertility, increased risk of arthritis and even cancer. White blood cells (WBC) are particularly sensitive to electromagnetic radiation and the risk of leukaemia is increased in those areas where exposure to such radiations is high e.g. around around power lines. Exposure to alternating magnetic fields accompanies exposure to electromagnetic radiations around power lines and from a variety of electrical appliances. Such exposure causes build up of serum triglycerides i.e. The fats found in blood stream that are implicated in heart diseases. Constant or frequent overexposure to such radiations may contribute to onset of heart problems.

A fully loaded 400 kv power line creates an electromagnetic field for 350 metres on either side of the line. This can generate electrical currents in the body, which produce an effect comparable to those that gives relief from pain. This effect of electromagnetic radiation on body is possibly due induced production of endorphins (natural pain-killers in body). It has been observed that continuous exposure to such radiations results in development of addictive dependency in cows and they start to prefer standing under power pylons for grazing or resting. They show withdrawl symptoms when away from such stimulation. It has been found that excessive concentration of positive ions builds up under power pylons and laboratory animals have died after constant exposure of 3 months to such conditions. A 50 Hz electromagnetic field has been found to adversely affect E. coli bacteria and water of wells underneath power lines has been shown to be devoid of naturally occurring bacteria present in waters away from such exposure. Laboratory experiments on rats, mouse and animal cells have shown an increased activity of enzyme ornithine decarboxylase in electromagnetic field of strength comparable to that produced by power lines. This enzyme speeds up the growth of cancer cells. Similar frequencies of radiation have been found to affect loss of calcium from the brain. it has been suggested that the problems arising from exposure around power lines may partly be due the effects of such radiation on calcium metabolism of the body.

When an object, living or non-living, enters an electromagnetic field, the field folds over the object so that its strength may become several hundred times more than that of unperturbed field. In the animal body, head houses the most vital organ, the brain which is most sensitive to electromagnetic field. Therefore, the head is the most affected part by the field-strength enhancement effect of electromagnetic field folded over animal body. Researches on the effects of electric blankets had shown alarming results because the body of user is entirely exposed to electromagnetic field for quite a few hours regularly. Among user women, seasonal (September to June) increase in miscarriages has been reported. The menstrual cycle is also disturbed in user women, which may be a contributing factor in the incidence of hormone related cancers such as breast cancers. The effect of electromagnetic field on such cancers is thought to be due to the effect of the field on melatonin production in the body. Electrically heated beds and blankets have also been linked to slower foetal development and learning problems in children, especually if mothers also used these during pregnancy.

The strength of electrical field drops off quite quickly with distance from the source and its frequency is clearly that of the source. However, the magnetic field fluctuates more, has ‘contaminating frequencies’ and its strength does not decrease with distance as quickly as that of electrical field. Furthermore, with increased distance, there is more likelihood that distribution of magnetic field over the body is uniform. A 400 kv power line may be generating underneath it a magnetic field of 1 microtesla (when current is around 100 A) to 10 microtesla (at greater loads, usual maxima being 5000 A) depending upon many variables like load, capacity, ground and weather conditions. It has been observed that people living near incoming supply in high-rise flats or ground floors are exposed to average magnetic field of 0.2 to 0.4 microtesla. These people have been found to be more susceptible to risks of heart diseases, cancers, depression and thyroid problems than those living on top floors away from the supply lines where magnetic field may be only around 0.015 microtesla. in cities, there may be continuous exposure to magnetic field of less than 0.1 microtesla in normal households. Such exposure may cause depressive feelings in the inmates. Electrical workers may experience exposure to levels up to 5 microtesla and the risks of various bodily and psychological disturbances to them may well be more harmful than moving in and out of similar field. Probably unbalanced, non-uniform magnetic field causes greater risk of various diseases and disturbances in the exposed subject than a balanced and unform field.

Apart from human beings, a number of detrimental effects of electromagnetic radiations have also been observed on animals and plants. It has been observed that earthworms are distributed and move away from underground power cables. Hens living near power lines lay scrambled eggs in thin shells, bees seal up their hives and become aggressive, cows loose apetite znd birds such as homing pigeons become disoriented. Plants exposed to electromagnetic radiation show disturbed root growth, seed germination, growth of pollen tubes, ion & water uptake and photosynthesis.

Exposure to microwaves is also increasing particularly in households due to increasing use of microwave-producing gadgets. Such exposure is also posing health risks as microwave exposure is known to cause cataracts and have detrimental effects on nervous and cardio-vascular systems.

LONG RANGE TRANSPORT (LRT) OF AIR POLLUTION

Atmospheric pollution becomes problem over a large area because atmosphere transports relatively uniform concentrations of air pollutant(s) over considerable distances. Rhdhe et al. (1982) categorized the scale of atmospheric transport as follows:

1. Local transport: This occurs from individual point or line source for a distance of few kilometres only. It is mainly associated with plumes and is affected by local meteorological conditions. As the plume disperses, most of the pollutant falls back to the ground as dry deposition.
2. Regional transport: This occurs to distances less than a thousand kilometres. At this scale, individual plumes merge together and development of a relatively uniform profile of pollutant after about 1-2 hours becomes possible. Such transport causes spread of air pollution problem from urban/industrial sources to the surrounding downwind countryside. In such transport, pollutants come down both by dry and wet deposition depending upon meteorological conditions.
3. Sub-continental and continental transport: Such transport occurs over several to a few thousand kilometres. In such transport, relatively uniform pollutant profile becomes well developed the pollution undergoes several diurnal cycles. At this scale, wet deposition of pollutants becomes more important than dry deposition and interchange of pollution between troposphere and stratosphere becomes possible.
4. Global transport: Such transport extends from a few thousand kilometres to the entire global atmosphere. At this scale, definable pathways of pollutant transport disappear due to inevitable mixing in atmosphere. Continental and global transports of air pollution are termed long range transport (LRT). Such transport requires an organized meteorological system of atleast synoptic scale that will allow movement of pollution without much dispersion or loss.

Most unnfavourable conditions for LRT are windy-blustry conditions associated with heavy rain and strong turbulent mixing. Under such conditions, any organised mass of pollution will almost immediately be blown apart. Scavenging from within and below the clouds will remove virtually all the pollutant material quite close to source region. Further, there would be little time available for secondary chemistry to develop.

Most favourable conditions for LRT involve circulation associated with the back side of a high pressure system where two major features become crucial:

1. Persistence of a synoptic-scale inversion over a wide area reducing vertical distribution of pollution and restricting it to a fairly shalow depth of atmosphere.

2. Existence of conditions allowing slow horizontal advection in the layer containing air pollution.

Both these situations are assisted by flat terrain that allows uninturrupted horizontal movement of air mass. During development of LRT, pollutants collect initially under the influence of a shallow, stable and high-pressure system that has been stagnating over a source region for previous several days. During this period, the surface wind speeds have been less than 3 metres per second, mixing heights below the inversion have been restricted to 1500 metres or less, hours of sunshine have been close to maximum possible and there have been no weather fronts or precipitation. Over the period, which is most likely to persist for four days, the concentration of air pollutants increases significantly, extensive secondary reactions occur and poor visibility persists. Under such circumstances, LRT of air pollution can occur in three major ways with first one having strongest impact.

1. The high pressure slowly begins to move out of the area and polluted air is drawn towards the trailing edge (in the back side) where it starts moving northwards (in northern hemisphere) in the prevailing circulation. If a weak cold or warm front is in the vicinity, transport is improved and is often beteer directed by the enhanced pressure gradient. Inversion and stable atmosphere often restrict LRT to layers below 700 mb pressure altitude and the polluted air mass may move several thousand kilometres without much dispersion or dilution. Separation from the friction layer near the surface is also important if polluted air mass is to maintain its cohesion. Over continental areas, extreme stability of lowest atmospheric layers in winter suggests that at airflow at 850 mb, pressure level might be the best indicator of LRT. During summers, transport is usually not so well defined as the solar heating and vertical convection tend to dominate the stability situation.

2. Variants to LRT situation provide smaller but still important concentrations of pollutants to great distances downwind of sources. If edge of a high is associated with cool, cloudy weather and a stiff breeze, the transport will be quite rapid in a dynamic and unstable atmosphere. high humidity and cloud cover will allow oxidation of precurssors such as SO 2 or NOx without a great deal of dispersion away from the air mass core. This results in transfer of moderate concentrations of pollutants that are not removed by rainwater because of the absence of enough vertical diffusion for precipitation.

3. If circulation system on the edge of a high pressure draws moist air from ocean regions, which then moves over source areas of pollution, weak turbulent mixing will draw the polluted material into the air stream. This material will mix rapidly through the depth of the air flow creating quite uniform and mild pollution concentrations. This pollution will be transported for considerable distances. If it meets a mountain barrier in the way, the mildly polluted air can be drawn up orographically and forced over the top. Pollutants are then scavenged resulting in mildly acidic rainfall on the windward side of mountain, which may persist for several hours. In the tropics, LRT largely depends on the persistence and frequency of trade winds associated with emission source regions. Transport occurs at the altitude of trade wind inversion and  in stable atmospheric conditions over long distances. This allows minimal dispersion of pollutant material in the air mass.

In southern hemisphere, there are very few air pollution sources and, therfore, no important LRT associated with air pollution. In the northern hemisphere, four major continental to hemispherical scale air pollution problems due to long range transport of air pollution. These are Arctic haze, Western Atlantic ocean air quality, Saharan dust and Asian dust.

Trajectory analysis

Measurements of LRT are often difficult and expensive. Therefore, trajectory analysis is often used to establish back trajectories (general source area of pollution origin) and forward trajectories (general location to which pollutants are being transported). Trajectories are calculated from synoptic level upper wind data and are normallly based on isobaric or isentropic principles. Two-dimensional models can not describe the vertical movements of either the airflow or the polluted air mass. Three-dimensional models, using a series of grid points at various altitudes have been designed to establish the sources of polluted air masses that have moved several thousand kilometres. Trajectories are best used as a support method to establish general transport movements and not to estimate the changes in pollution concentrations over the time. Benefits of such use are:

• Support for chemical tracer experiments from different source regions;
• Simulation of dry deposition;
• Evaluation of acute air pollution problems;
• Establishment of the source of a chronic pollution problem. At best, trajectories show general accuracy for five days assuming that air flow is consistent with little vertical or horizontal changes.

Most often trajectories lose accuracy after 48 hours since spatial distribution of upper synoptic grid and the number of measurements from them are too thin to obtain accurate interpolations of air flow variations. Distortions occur with the presence of turbulent eddies, evolving synoptic patterns, increasing diffusion and inaccuracies in determination of mean wind. Trajectory analysis fails in presence of fronts or other rapidly changing atmospheric conditions.

CLASSIFICATION OF CLIMATE

The climate is most important factor controlling the environment. The type of soil and the native vegetation in a given region are basically the product of the climate of the area. The scientific study of climate requires a scheme of climate classification. Such schemes aim to categorize all the variations in the climates found in different areas into several clearly defined and easily distinguishable groups. Many useful systems of climate classification can be devised by taking different weather elements such as temperature, pressure, winds, precipitation as the basis of classification. the distribution of natural vegetation and soils may suggest still other types of classification schemes.

Temperature as basis of climate classification
The general parallelism of isotherms with parallels of latitude was perhaps the first basis of climate classification. With intelligent application, temperature has been made a fundamental factor in most of the schemes. Three major climate groups are clearly recognizable on the basis of this criterion:

1. Equatorial tropical group:  characterized by uniformly warm temperature throughout the year and absence of a winter season.
2. Middle-latitude group:  characterized by alternating summer and winter seasons.
3. Polar-arctic group:  characterized by the absence of true summer season.

A common boundary between polar-arctic climates and middle-latitude climates is 10 degrees celsius (50 degrees F) isotherm of the warmest month (i.e. july in northern hemisphere). The boundary between middle-latituse and equatorial climates is marked by 18 degrees celsius (64.4 degrees F) isotherm of the coldest month.

The use of temperature alone as the basis of climate classification is unsatisfactory because humid and desert regions are not distinguished in such scheme.

Precipitation as basis of climate classification
The climate map in such a scheme would be same as the mean annual rainfall map. Such system may be refined by subdividing classes according to distribution of precipitation throughout the year, whether uniform or seasonal. However, such classification scheme fails because it groups cold arctic climates together with hot deserts of low latitudes controlled by air temperature. The cold climates, in general, are effectively humid with same meager precipitaion that produces very dry deserts in hot subtropics and tropics.

Vegetation as basis of climate classification
Different plant types require special condition of temperature and precipitation for their survival. Thus, plants form an index of climate and limits of growth of key plant types provide meaningful boundaries of climstic zones. There is much merit in such vegetational zones based climate classificstion scheme. However, vegetation is an effect rather than a primary cause of climate. Therefore, it can not give so satisfactory a climate classification as the one based on the primary cause(s) of climate.

Koppen climate classification system
After various attempts of classification schemes based on some single characteristic feature, it became evident that a meaningful system should devise climate classes that combine temperature and precipitation characteristics but also set limits and boundaries that fit into obviously known vegetational distributions. Dr. Wladimir Koppen (1918) devised such a system that was later revised and extended by him and his students. this Koppen climate classification system has become most widely used system for biogeographical purposes.

Koppen system is strictly empirical in nature. Each climate group is defined according to fixed values of temperature and precipitation, computed according to averages of the year or of individual months. No attention is paid to the causes of climate in terms of pressure belts, wind belts, air masses, air fronts or storms. A given place can be assigned to a particular climate subgroup solely on the basis of the records of temperature and precipitation of that area provided that the records are long enough to yield meaningful averages. Since air temperature and precipitation are most easily obtainable surface weather data, the system has great advantage that the areas covered by each subtype of climate can be computed or estimated for large regions of the world. This system thus, incorporates an empirical-quantitative approach.
Koppen system has a shorthand code of letters disignating major climate groups (A, B, C, D), subgroups within major groups(S, W, f, m, s, w) and further subdivisions to distinguish particular seasonal characteristics of temperature and precipitation (a, b, c, d, h, k).

Air mass source regions and frontal zones as basis of climate classification

Increasingly detailed studies of vsrious charateristics of weather elements, global circulation, air mass properties, source regions and cyclonic storms have yielded many principles related to the causes of weather patterns and their seasonal variations at global scale. Therefore, such knowledge has also been incorporated in the explanatory-descriptive system of climate classification based on the cause and effect. Thus, such system is based on the location of air mass source regions and nature and movement of air masses, fronts and cyclonic storms. Koppen code symbols have been incorporated into this system by interrelating both systems. This system simply provides a reasonable scientic explanation for the existence of Koppen’s climate groups.

Plant Diversity in the Indian Gene Centre