I organic air pollutants I 1 Volatile Organic Compounds (vocs)




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I.3.2.2. Electromagnetic Environment


Electric Field of the Earth


The electric field of the Earth is produced by the local build-up of electric charges at the surface of the Earth (negative) and in the atmosphere in contact (in excess, positive). The gradient thus formed reaches values of 120-150 V/m with an influence to humans of 200-250 V foot to head. These static electric fields vary greatly in value according to the weather, cosmic phenomena, topography; the gradient is very high when fog and negative during rainy weather.

Healthy people, used to the open-air life easily undertake the Earth electric fields changes (e. g. during storms), whereas the cardiac or other sufferers may have strong physiological reactions to these changes.


Magnetic Field of the Earth


The Earth may be compared with a huge magnet whose magnetic field has a low intensity at its surface of 0.5 Øersted. This field varies slightly in magnitude during the day and also during the month (<1% variation). These fluctuations define the magnetic calm. During solar activity intensifications, magnetic storms occur which may affect labile people (those with circulatory, neural diseases, etc.).

Electromagnetic Man-Made Waves


Since the turn of the century, and more precisely, since the 1950-s, the humanity has surrounded itself with artificial electric and magnetic fields as a result of the increasing use of electricity as an indispensable part of every day life. A short history of EM radiation usage would be very difficult to draw, however there are around 90 years since public radio transmissions began and 60 years since radar was first used. Today, it is believed that our exposure is 200 million times greater than in the beginning of the century.

The Table I.3.3 lists a number of the most important man-made EM waves along with their corresponding frequencies and wavelengths.


Table I.3.3. Characteristics of man-made waves


Application

Frequency (Hz)

Wavelength (m)

Power transmission

50

6000 km

Sub-sea communications

75

4000 km

Audio (20 Hz to 20 kHz)

1 kHz

300 km

Long wave radio

100 kHz

3 km

Medium wave radio

1 MHz

300 m

FM radio

100 MHz

3 m

Terrestrial TV broadcast

600 MHz

500 mm

Mobile phones

900 MHz

330 mm

Radio astronomy

1.42 GHz

214 mm

Global positioning system

1.5 GHz

200 mm

Mobile phones

1.8 GHz

165 mm

Microwave ovens

2.45 GHz

122 mm

Wireless networks radar

5 GHz

60 mm

Imaging radars

30 GHz

10 mm

Fiber -optic communications

30 THz

10 m

Fiber-optic communications

230 THz

1.3 m


As presented here, artificial EM waves have single, sharp frequencies, unlike natural radiation, where the range is broader. Moreover, some wavelengths of man-made EM waves are similar to those of natural waves (i.e. 214 nm corresponds to both the hydrogen line and radio astronomy emissions; 10 mm corresponds to far infra-red radiation as well as the fiber optic communications).

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