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28 Nov

Ions- The Myth Explained

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Negative Ions In Lightening Negative Ions In Lightening

 Air pollution is a serious, though often unrecognized health problem. Epidermiological

 

The Positive Health Benefits of Negative Ions

 

By Jim English

 

Air pollution is a serious, though often unrecognized health problem. Epidemiological studies consistently point to a direct link between urban air pollution – especially particulate pollution created by combustion powered vehicles and power generation plants – and cardiovascular and pulmonary diseases. (1) Long-term exposure to particulate pollution – tiny particles smaller than 10 microns (a human hair is 70 microns wide) – is known to increase illness and death rates from lung cancer, chronic obstructive pulmonary disease and emphysema. Additionally, exposure to other airborne pollutants, including sulfur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3), is associated with development of asthma, bronchitis, and respiratory infections. (2)

 

European researchers investigated the risks of long-term exposure to traffic pollution in a study examining 5000 volunteers selected from the ongoing Netherlands Cohort study on Diet and Cancer (NLCS). They discovered that people living near major roads (and therefore exposed to higher levels of traffic-related air pollution) were more likely to die from cardiopulmonary disease or lung cancer than their rural peers, leading the authors to conclude that 'long-term exposure to traffic-related air pollution may shorten life expectancy. (3)

 

Air Pollution Linked to Heart Damage

 

In addition to causing lung damage, air pollution is now also recognized as a threat to cardiovascular health. Reporting in the March 6, 2002 Journal of the American Medical Association (JAMA), researchers examined long-term health data on 500,000 individuals to compare increases in air pollution levels with incidence of death. They discovered that when air pollution levels suddenly increased, in addition to expected increases in deaths from asthma, pneumonia, and emphysema, there was an unexpected increase in the number of deaths related to heart attacks and stroke. Most surprising was the finding that when air pollution levels rose, so did deaths from all causes, not just those related to the heart and lungs (Fig. 1). (4)

 

 

 

One possible explanation for the increase in cardiovascular-related deaths is that air pollution causes oxidative stress that, in turn, triggers an inflammatory response in the lungs that leads to the release of chemicals that impair heart function and blood pressure.

 

This was shown to be the case when scientists working in the Netherlands exposed rats to high levels of particulate air pollution. Following exposure, the researchers found that plasma levels of fibrinogen were elevated by 20 percent, which could presumably increase blood viscosity, leading to decreased tissue blood flow. They also measured a 400 percent jump in tumor necrosis factor (TNF)-alpha, and a 350 percent increase in nitric oxide synthase (NOS) in lung fluids. The researchers speculated that as particulates lodge in lung tissues they induce an increase in the production of nitric oxide (NO). Under normal conditions nitric oxide is an important neurotransmitter that aids numerous signaling pathways involved in motor learning, protein modification, arterial dilation and immune defense. But when conditions trigger the overproduction of NO as seen in the Netherlands study, the result is serious damage to the endothelial cells lining the blood vessels of the lungs. (5)

 

When Japanese researchers exposed guinea pigs to particulates from diesel exhaust, the lungs showed a significant elevation of leukotrienes and eosinophils, two important biomarkers of inflammation and cytotoxicity commonly observed in cases of chronic obstructive lung disease (COLD). The researchers noted that these findings indicate that chronic exposure to diesel exhaust induces continuous inflammation and overproduction of mucus and phospholipids in the lung. (6)

 

Another mechanism implicated in air pollution-related heart failures involves bone marrow and atherosclerotic plaques. Researchers in Vancouver, British Columbia found that exposure to high levels of air pollution stimulates bone marrow to release leukocytes and platelets that accumulate preferentially in pulmonary capillaries. In addition to causing damage to lung tissues, the researchers also observed that inhalation of particulate pollution causes changes in atherosclerotic plaque lesions that make the deposits more vulnerable to rupture.

 

They postulated that exposure to particulate air pollution induces a systemic inflammatory response that includes the release of inflammatory mediators that stimulate bone marrow to release leukocytes and platelets, leading to lung inflammation and changes of atherosclerotic plaque, making them more vulnerable to rupture. (7)

 

Diabetics and Elderly at Increased Risk

 

Diabetics are particularly susceptible to cardiovascular damage caused by airborne pollution. A recent study published in the journal Epidemiology examined Medicare records and hospital admissions in US cities: Chicago, Detroit, Pittsburgh, and Seattle. Looking at records from 1988 to 1994 they found that diabetics were twice as likely as non-diabetics to be admitted to a hospital with a cardiovascular problem caused by airborne particulate pollution. They also found that persons 75 years of age and older also faced a higher risk of cardiovascular injury. (8)

 

Children and Air Pollution

 

Children are particularly at risk for health issues related to air pollution. Chronic exposure to particulates, sulfur dioxide and nitrogen dioxide have been associated with up to 300 percent increases in nonspecific chronic respiratory symptoms. Exposure to automotive pollution, particularly from truck and diesel exhaust, has been shown to cause significant increases in respiratory symptoms and decreased lung function. (9)

 

To examine the relationship between traffic-related air pollution and childhood development of asthma and other childhood respiratory diseases and infections, researchers in the Netherlands looked at data from some 4,000 babies born in the Netherlands. The health of the children was linked to measurements of traffic-generated air pollution (nitrogen dioxide, particulate matter less than 2.5 microns in diameter, and soot) in the homes of each subject. Their study found that, by the age of two years, children exposed to higher levels of air pollutants were more likely to suffer from wheezing, physician-diagnosed asthma, ear/nose/throat infections, and flu/serious colds. (10)

 

Part of the problem for children is that studies show that – relative to their size – children inhale more deeply and trap more airborne particles and pollutants in their lungs than either adolescents or adults. (11) Children also have higher metabolic rates than adults, breathe more than adults, and spend more time outdoors than adults, exacerbating their susceptibility to pollution-related health problems.

 

Children's Growth Stunted

 

When Polish researchers examined the effects of air pollution in Krakow they discovered that children living in those areas with the highest levels of air pollution suffered from stunted growth. After collecting data on 958 children and assessing body growth rates by height changes they found that body growth rates for children from the most highly polluted area was lower by 1.5 cm over a 2-year period than those from the control area. The compromising effect of air pollution on height gains was about the same for both short and tall children. (12)

 

Air Pollution and DNA Mutations

 

New research shows that the health threat posed by air pollution may actually affect children even before they are born. On December 9, 2002, Canadian researchers published a study revealing that animals exposed to polluted air close to a steel mill suffered genetic damage and produced fewer offspring. Most alarming was the discovery that damaged DNA was being passed on to offspring by their fathers. While virtually all mutations were inherited from the father mice, the researchers said this doesn't mean that females are not susceptible. What it does suggest is that steel workers, who are mostly male, may be at extra risk of similar damage.

 

Christopher Somers, James Quinn, and colleagues published an earlier study that found that gulls living near a steel mill on Lake Ontario suffered from genetic mutations. In a current study the researchers raised two groups of mice – the first a half-mile downwind of a steel mill on Lake Ontario, and the second about 20 miles away. The mice breathing the polluted air had twice as many mutations in their DNA as the mice breathing fresh country air. (13)

 

The findings suggest that steel mill workers and people living near those mills should be checked for damage to their health, said the researchers, at McMaster University in Hamilton, Ontario. "Our findings suggest that there is an urgent need to investigate the genetic consequences associated with exposure to chemical pollution through the inhalation of urban and industrial air."

 

Ironically, the study was originally aimed at showing how efforts to clean up pollution around the steel mill had improved the environment. 'This had been one of the most polluted places, if not the most polluted place in Canada,' stated Christopher Somers, one of the lead researchers. 'There has been a concerted effort to clean up Hamilton harbor and reduce air emissions.' The experiment had been aimed at showing these had helped. ''We haven't really seen that,'' he said.

 

Protecting Your Lungs

 

While government, business and environmental interests wrangle over a morass of economic, legislative and technological solutions for cleaning up polluted air, the vital issue facing individuals is how best to protect their health. Currently over 75 million people in the US live in counties where the air concentrations of particulate matter smaller than 2.5 microns (PM2.5) exceed safe levels (Fig. 2.). (14)

 

 

 

While living away from polluted urban centers is an obvious choice, this option is not always possible. Nor is it always effective. Air currents and weather patterns can move polluted air out of urban manufacturing centers and into rural areas where pollution can concentrate to a dangerous degree. Additionally, modern farming produces more food with fewer workers, using improved productivity methods that increasingly rely on the use of agricultural pesticides and chemicals, and irrigation pumps and tractors powered by diesel engines. (15)

 

Staying indoors does not guarantee better air quality, either. Several recent studies have indicated that much of the significant health risk associated with exposure to fine particles actually occurred indoors. (16) And many individuals at increased risk of health complications following exposure to high particle concentrations, such as the elderly and those suffering from cardiovascular and pulmonary diseases, may spend more than 90% of their time indoors, raising new concerns about the relationship between outdoor particle concentrations and those found in indoor microenvironments. (17)

 

Air Purifiers

 

As the scope of air pollution related health problems grows, so too does the number of people turning to air purifying solutions for protection. Home air filtration products offer a number of options, including electrostatic, UV radiation, water and advanced HEPA filtration technologies. Until recently, these products – many engineered for entire houses and buildings – were bulky and expensive to install and maintain, placing them out of reach for most people. Recently, a number of consumer products have become available utilizing ion-generating technology to eliminate airborne pollutants, allergens and viruses from immediate breathing spaces.

 

These devices work by generating a flow of negative ions that charge and bind together airborne particulate matter, which then clumps and precipitates out of the air. Ion generating devices have been shown to be effective against dust, cigarette smoke, pet dander, pollen, mold spores, viruses, and bacteria. In addition to eliminating harmful particulates from the air, negative ions also have a number of unique health benefits.

 

Positive Ions - An Ill Wind Blows

 

Early clues about the biological effect of ions on human health appear as reports of increased irritability, migraine attacks and thromboembolism in response to alterations in atmospheric electrical states that accompany incoming weather fronts. (18)

 

Scientific evidence began to mount in the 1970s when researchers measured metabolic changes in mice and rats in response to changes in ion charge (negative or positive) and concentration, including alterations in serotonin levels and recovery from illness. When exposed to positive ions (which accumulate in the atmosphere at the beginning of a storm) researchers routinely noted that animals became agitated, aggressive and were more prone to respiratory illness. Furthermore, when mice were infected with influenza virus and housed in an environment depleted of all ions, death rates increased, indicating a previously unknown benefit on overall health. (19)

 

Later, researchers measured the impact of atmospheric electricity on human subjects by monitoring daily changes in urine excretion of neurohormones in samples gathered from 1,000 volunteers exposed to positive ions generated 1 to 2 days prior to the arrival of a storm front. By measuring the changing levels of neurohormones in the 24-hour urinary output of the subjects during normal and weather-stress days, the researchers compiled a profile of changes in levels of serotonin, 5-HIAA (5-hydroxyindole acetic acid, a serotonin metabolite), adrenaline, noradrenaline, histamine and thyroxine.

 

The researchers found that the electrical charges (positive ionization) engendered by every incoming weather front produce a release of serotonin. (20) They further identified three classes of weather sensitivity reactions:

 

1. serotonin hyperproduction causing a typical irritation syndrome;
2. adrenal deficiency producing a typical exhaustion syndrome;
3. hyperthyroidism with subclinical 'apathetic' thyroid symptoms.

 

Noting that these conditions occur during annual wind storms (Sirocco, Sharav and Santa Ana winds), the authors stated that the effects, "which are mainly due to positive ionization of the air," could be "prevented by negative ionizing apparatuses or specific drug treatment." (21)

 

Further evidence of the influence of ions appeared when scientists exposed mice to an atmosphere enriched with either positive or negative ions. While negative ions had no negative effect on the mice, positive ions caused elevations in norepinephrine levels within one day. When exposure to positive ions was continued for longer periods, ranging from 3 to 10 days, norepinephrine levels dropped. The author noted that the results showed that "positive ions cause stress after short time application in excess. After longer exposure, a state of exhaustion can be observed in the form of a lowered norepinephrine level." (22)

 

Health Benefits of Negative Ions

 

Just as positive ions build up in the atmosphere prior to a storm front, negative ions accumulate following a storm. This surfeit of negative ions has long been associated with improvements in mood and physical health. Research conducted in the last decade has begun to support the view that negative ions have a net positive effect on health.

 

One of the most tantalizing hints regarding negative ions and health surfaced when German researchers discovered a link between catecholamine regulation and lifespan after depriving experimental animals of negative ions. First, researchers at the Goldstein and Lewin Dept. of Medical Research in Stahnsdorf, Germany isolated mice and rats in air-tight, sealed acrylic cases. Next, they filtered the ambient air to remove all negative ions from the sealed cases. Their research led to the discovery that a prolonged deficiency of negative ions led to an accelerated rate of death for the experimental animals. Examination of the animals led researchers to conclude that the results 'strongly suggest that animal death is related to disturbances in neurohormonal regulation and pituitary insufficiency. (23)

 

Researchers at the Russian Academy of Sciences in Moscow discovered that negative ions are able to help protect the body from induced physical stress. When the researchers immobilized rats and exposed them to negatively charged air ions they discovered that the ions prevented the development of pathological changes characteristic of acute stress that are observed in untreated rats. The protective action of negative air ions was observed in all the experimental animals independently of their types of behavior. (24)

 

British researchers at the Centre for Sport and Exercise Sciences in Liverpool exposed male subjects to negative ions and measured physiological responses, including body temperature, heart rate and respiration, while at rest and during exercise. Negative ions were found to significantly improve all physiological states, particularly during rest. Most important was the finding that negative ions are "biologically active and that they do affect the body's circadian rhythmicity." (25)

 

Another clue to the role of negative ions in health comes from Russian research conducted at the Institute of Theoretical and Experimental Biophysics of the Russian Academy of Sciences, in Pushchino, Russia. Researchers found that exposure to negative ions increased levels of the protective antioxidant enzyme superoxide dismutase (SOD) in mammalian erythrocytes. The researchers also discovered minute amounts of H2O2 (hydrogen peroxide), writing, "The primary physiochemical mechanism of beneficial biological action of negative air ions is suggested to be related to the stimulation of superoxide dismutase activity by micromolar concentrations of H2O2 (hydrogen peroxide)." (26)

 

Summary

 

While progress has been made in some areas of air pollution, such as reductions in emissions of lead, sulfur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3), air pollution, particularly from particulates, remains a serious health problem. In addition to damaging the lungs and heart, air pollution is now recognized as being especially harmful to children, the elderly, and select sensitive populations, such as those afflicted with diabetes, cardiopulmonary diseases and other debilitating illnesses.

 

To address air pollution-related health problems a growing number of people are using personal and home air filtration products that generate negative ions to charge and precipitate airborne particulate matter for removal to create localized zones of improved air quality.

 

Consumer devices that utilize negative ion-generating technology have been shown to eliminate airborne pollutants, dust, cigarette smoke, pet dander, pollen, mold spores, viruses, and bacteria from the air. Negative ions have long been attributed to improvements in mood and physical health. Research supports the view that negative ions have a net positive effect on health, including improved mood, stabilized catecholamine regulation and circadian rhythm, enhanced recovery from physical exertion and protection from positive ion-related stress and exhaustion disorders.

 

References

 

1. Vrang ML, Hertel O, Palmgren F, Wahlin P, Raaschou-Nielsen O, Loft SH. Effects of traffic-generated ultrafine particles on health. Ugeskr Laeger 2002 Aug 19;164(34):3937-41.
2. Polosa R, Salvi S, Di Maria GU. Allergic susceptibility associated with diesel exhaust particle exposure: clear as mud. Arch Environ Health 2002 May-Jun;57(3):188-93.
3. Hoek G, Brunekreef B, Goldbohm S, Fischer P, van den Brandt PA.Association between mortality and indicators of traffic-related air pollution in the Netherlands: a cohort study. Lancet. 2002 Oct 19;360(9341):1184-5.
4. JAMA March 6, 2002;287:1132-1141.
5. Ulrich MM, Alink GM, Kumarathasan P, Vincent R, Boere AJ, Cassee FR.. Health effects and time course of particulate matter on the cardiopulmonary system in rats with lung inflammation. J Toxicol Environ Health A 2002 Oct 25;65(20):1571-95.
6. Ishihara Y, Kagawa J. Dose-response assessment and effect of particles in guinea pigs exposed chronically to diesel exhaust: analysis of various biological markers in pulmonary alveolar lavage fluid and circulating blood. Inhal Toxicol 2002 Oct;14(10):1049-67.
7. van Eeden SF, Hogg JC. Systemic inflammatory response induced by particulate matter air pollution: the importance of bone-marrow stimulation. J Toxicol Environ Health A 2002 Oct 25;65(20):1597-613.
8. Zanobetti A, Schwartz J. Cardiovascular damage by airborne particles: are diabetics more susceptible? Epidemiology 2002 Sep;13(5):588-92.
9. Nicolai T. Environmental air pollution and lung disease in children. Monaldi Arch Chest Dis 1999 Dec;54(6):475-8.
10. Brauer M, Hoek G, Van Vliet P, et al. Air pollution from traffic and the development of respiratory infections and asthmatic and allergic symptoms in children. Am J Respir Crit Care Med 2002 Oct 15;166(8):1092-8.
11. Inhalation Toxicology, Sept. 1998;10:831-842.
12. Jedrychowski W, Maugeri U, Jedrychowska-Bianchi I. Body growth rate in preadolescent children and outdoor air quality. Environ Res 2002 Sep;90(1):12-20.
13. Christopher M. Somers, Carole L. Yaukdagger, Paul A. Whitedagger, et. al.. Air pollution induces heritable DNA mutations. Proc. Natl. Acad. Sci. USA, Vol. 99, Issue 25, 15904-15907, December 10, 2002.
14. EPA, Latest Findings on National Air Quality: 2000 Status and Trends.
15. Smog Check II for All. San Jose Mercury News, Sep. 29, 2002.
16. R.B. Mosley, D.J. Greenwell, L.E. Sparks, Z. Guo, W.G. Tucker, R. Fortmann, C. Whitfield. Penetration of Ambient Fine Particles into the Indoor Environment. Aerosol Science and Technology: Vol. 34, Num. 1; Jan. 2001.
17. J. Thornburg, D.S. Ensor, C.E. Rodes, P.A. Lawless, L.E. Sparks, and R.B. Mosley. Penetration of Particles into Buildings and Associated Physical Factors, Part I: Model Development and Computer Simulations. Aerosol Science and Technology: Vol. 34, Num. 3; March 2001.
18. Sulman FG. The impact of weather on human health. Rev Environ Health 1984;4(2):83-119.
19. Krueger AP, Reed EJ.Biological impact of small air ions. Science 1976 Sep 24;193(4259):1209-13.
20. Sulman FG. Migraine and headache due to weather and allied causes and its specific treatment. Ups J Med Sci Suppl 1980;31:41-4.
21. Sulman FG, Levy D, Lunkan L, Pfeifer Y, Tal E. New methods in the treatment of weather sensitivity. Fortschr Med 1977 Mar 17;95(11):746-52.
22. Udermann H, Fischer G. Studies on the influence of positive or negative small ions on the catechol amine content in the brain of the mouse following shorttime or prolonged exposure. Zentralbl Bakteriol Mikrobiol Hyg [B] 1982 Apr;176(1):72-8.
23. Goldstein N, Arshavskaya TV. Is atmospheric superoxide vitally necessary? Accelerated death of animals in a quasi-neutral electric atmosphere. Z Naturforsch [C] 1997 May-Jun;52(5-6):396-404.
24. Livanova LM, Levshina IP, Nozdracheva LV, Elbakidze MG, Airapetiants MG. The protective action of negative air ions in acute stress in rats with different typological behavioral characteristics. Zh Vyssh Nerv Deiat Im I P Pavlova 1998 May-Jun;48(3):554-7.
25. Reilly T, Stevenson IC. An investigation of the effects of negative air ions on responses to submaximal exercise at different times of day. J Hum Ergol (Tokyo) 1993 Jun;22(1):1-9.
26. Kosenko EA, Kaminsky YuG, Stavrovskaya IG, Sirota TV, Kondrashova MN. The stimulatory effect of negative air ions and hydrogen peroxide on the activity of superoxide dismutase. FEBS Lett 1997 Jun 30;410(2-3):309-12.

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NIELS JONASSEN

 

 

 

 

 

 

 

 

 

 

 

IONIZATION

 

 

 

 

 

 

 

 

 

LABORATORY OF APPLIED PHYSICS

 

TECHNICAL UNIVERSITY OF DENMARK

 

JANUARY 1989

 

 

 

A LITTLE HISTORY

 

Almost three centuries have passed since W.Wall in 1708 made the first known observation of the fact that some processes in the atmosphere are electrical by nature by noting that the sparks one might draw from amber rubbed in a suitable manner “seems in some degree to represent thunder and lightning”.

 

This idea of Wall’s was pursued by several well known scientists, foremost among these Benjamin Franklin who in 1750 suggested an antennae to be placed in a high tower. When a thunder cloud passed the tower one should then be able to draw electric sparks from the antennae. The (regrettable) fact that no sufficiently high tower was at hand in Philadelphia at that time caused the French scientist Dalibart to be the one (in 1752) to prove the identity between a lightning discharge and an electric spark. I should be mentioned, however, that B.F one month later, without knowing Dalibart’s experiment, repeated this in his famous kite experiment, and, no surprise, with the same result.

 

On the other hand, maybe Ben Franklin was lucky, when on considers the fate of his contemporary, Professor Richardson, in St. Petersburg (Leningrad), who a few years later was killed when lightning struck the “antenna” he had mounted in front of him on his desk.

 

During the next century and a half atmospheric electric processes were investigated in great detail and by the end of the 19th century the following model was more or less accepted. An electric field exists in the (lower) atmosphere, normally directed towards ground indicating the presence of a negative surface charge on the earth. It was believed that the earth actually had a net charge, and since the air was also considered a perfect insulator, charge could only be transported to or from the earth in connection with evaporation of water vapour, rain (negative charge to the ground).

 

This simple model seemed to fit observed changes in the field reasonably well, but already as early as 1785 Coulomb had noticed, that an insulted charged body would eventually loose its charge when it was left alone surrounded by atmospheric air. He suggested this effect to be caused by an attraction of oppositely charged dust particles or water vapour from the air, and even if this explanation is rather insufficient, it does contain the certain conductivity. The importance of this observation, however, was not realized, and neither was a similar observation by Mateucci (about 1850), and it was not until the (independent) investigations by Linss and Schuster around 1890 that it was accepted that atmospheric air is not a perfect insulator.

 

The question of the nature of the mobile charge carriers, necessary for rendering the air conductive, however, gave rise to another question. Why does the negative charge on the earth not become neutralized, as positive charge is brought to the surface by the electric field? A simple calculation would show this to happen in less than an hour, and yet the charge does still appear to happen in less than an hour, and yet the charge does still appear to be there. The answer is that we have not mentioned a very important factor, the thunderstorms.

 

In a very summaric way we can give the following presentation of what is usually called the atmospheric electric circuit, Figure 1.

 

 

 

 

Figure 1. The atmospheric electric circuit.

 

 

 

To the left are shown fair-weather conditions, where the field is directed towards ground an thus will bring positive charge to the surface. Most of the field lines end on positive space charges in the lower atmosphere, while some extend all the way to the so-called atmospheric electric exchange layer (about 60 km up), the lower part of the ionosphere. The necessary field distribution is maintained by the thunderstorms, shown in the right hand side of the figure. A thunderstorm has (normally) a negative basis and a positive top thus bringing negative charge to the ground. The (downward) fair-weather field is approximately 100 – 200 V*m-1 while the opposite field under a thunder cloud may be some 10,000 V*m-1 . The total number of thunderstorms active at any given moment may be about 2000 and the total current to (and from) the earth about 1600 A, which on the other hand only amounts to about 3*10-12 A*m-2 in fair-weather regions.

 

 

 

And let us now turn to the question of the charge carriers, the atmospheric ions.

 

ATMOSPHERICIONS

 

 An air ion is formed, when a neutral oxygen or nitrogen molecule looses an electron and is left as a singly charged positive elementary ion. Within less than a microsecond the electron will combine with (usually) another neutral molecule forming a singly charged negative elementary ion, Figure 2.

 

 

 

 

 

 

Small ions

 

Both polarities of elementary ions will within a fraction of a second by polarization bind a number of 10-20 molecules (water, nitrogen oxides and others) round itself forming a molecular cluster. When we talk about ions, we are usually only referring to these small ions.

 

 

 

Large ions

 

Any atmosphere will contain aerosol particles or condensation nuclei in numbers from a few thousand to several hundred thousand per cm3. These are particles or molecular clusters with radii from maybe 10nm to about 1 m. If a small ion collides with a condensation nucleus the two may form a so-called large ion.

 

 

 

Ion mobility

 

The quantity most suitable for characterizing the electrical behaviour of an ion is its mobility. If an ion with a charge e is exposed to an electric field with the strength E, it is per definition acted upon by an electrical force F given by

 

 

 

F = E*e                    (1)

 

 

 

The result is, however, not as one might expect an accelerated but a uniform motion with the constant velocity v given by

 

 

 

v = k*E                    (2)

 

 

 

The factor of proportionality k is called the mobility of the ion. Its unit is

 

m2V-1s-1.

 

The ion will actually get an acceleration E*e/m, where m is its mass, and move in the direction of the field with increasing velocity. After a distance equal to the mean free path it will collide with (normally) a molecule, loose all its field energy and field velocity, and start all over again. Hence the apparent uniform motion.

 

 Small ions are found to have mobilites in the range 1*10-4 to 2*10-3 m2V-1s-1  and large ions in the range 3*10-8 to 8*10-7 m2V-1s-1. Sometimes the range in between is also populated. These ions are called intermediate or Langevin-ions.

 

 It has often been discussed if atmospheric ions are distributed at discrete mobilities or more or less uniformly over the whole range of mobilities

 

 

 

Small negative ions seem to have mobilities very close to 1.8 – 2*10-4 m2V-1s-1 and small positive ions about 1.2 -1.4*10-4 m2V-1s-1 , The difference probably reflecting a difference in the number of molecules in the cluster. Large ions on the other hand may occupy whole mobility bands depending upon the nature and size distribution of the condensation nuclei available.

 

 

 

ION SOURCES

 

An air molecule may receive the necessary ionization energy either from a colliding particle or from a quantum of electromagnetic radiation energy.

 

          “Natural air ions are (in the lower atmosphere) predominantly produced by radiation from radioactive materials in the soil, in building materials and first of all in the air (radon and its airborne daughter products). Although all three types (alpha, beta and gamma radiation) can ionize the air, in practice only alpha radiation needs to be considered.

 

 

 

RADIOACTIVE IONIZATION

 

Alpha particles are emitted from a decaying radioactive atom with energies in the order of 4 to 8 MeV (or 6 - 13*10-13 J). On its way through the surrounding air an alpha particle will knock off electrons from neutral oxygen or nitrogen molecules, Figure 3, at the expense of about 34 eV per successful collision.

 

          After having travelled a distance from 2 to 7 cm the alpha particle has lost its energy (and velocity) and produced about 200,000 ion pairs along its track.

 

 

          This mechanism of ion production can also be utilized technically, as will be explained later, but the most commonly used method of producing air ions is, however, based on the effect of electric fields.

 

 

 

FIELD IONIZATION

 

If the air is exposed to an electric field the ions (caused by the natural radiation) will move in the field and collide with (neutral) molecules after having travelled the mean mean path, characteristic for the ions. One might expect this to cause ionization in the same manner as with collisions between alpha particles and molecules. The energy of the ions at the end of the mean free path is, however, not, even at very high field strengths, high enough to knock off an electron. The electrons freed by the natural radioactive ionization, will of course also move under the action of the field, and although they over the same distance receive the same energy as any other particle carrying a single elementary charge, the mean free path is so much longer for an electron, that it, when exposed to an electric field of about 3*106 Vm-1 (with plane electrodes and at atmospheric pressure), is able to ionize molecules of the air. The electron being knocked off the molecule will also be accelerated and ionize and so on in the whole region, where the field strength exceeds the critical so-called break down field strength.

 

 

 

Field ionization is usually achieved by keeping a set of sharp points or thin wires at high potential (2-20 kV) with respect to some counter electrode, which may even be the walls of the room.

 

 

 

The break down field strength E0 has the following values

 

For points

 

E0 = (300 + 18/r)*104 Vm-1               (3)

 

And for wires

 

E0 = (300 + 9/r)*104 Vm-1                  (4)

 

 

 

Where r is radius of the points and wires respectively (in m).

 

          It appears that the break down field given by (3) and (4) is higher than for a parallel electrode system, but because of the field deformation caused by point and wire electrodes, the necessary voltage is much lower than would be the case with parallel plates. Usually the voltage of the electrodes (points or wires) are kept at such a value, that E0 is exceeded in a region of some mm from the electrodes, Figure 4. In this region we then have so-called corona discharge where ions are formed and separated by the field. If the voltage of the electrodes is positive the negative ions will move to the electrode and become neutralized here while the positive ions will be repelled and move away from the electrode, possibly aided by an air current.

 

 

 

 

The necessary field at the electrodes may, however, also be supplied by the charge to be neutralized, as it will be explained later on (passive ionizers).

 

 

 

REMOVAL OF IONS

 

 

 

An ion has a limited lifetime. It may be moved by an electric field to some surface where it may become neutralized. It may combine with oppositely charged ions or particles and hence cease to exist as an ion, or in the case of a small ion combine with aerosol particles and then either be neutralized or become a large ion, and in both cases no longer exist as a small ion. Figure 5. The rate of combination is proportional to the concentrations of the combining species.

 

 

          Let us for example consider a room with a small ion concentration of say 1000 cm-3 and a low aerosol concentration of similar magnitude. If now a candle or a cigarette is lit in the room, the aerosol concentration may almost momentarily increase to maybe 100,000 cm-3 and the small ion concentration decrease to maybe 50-100cm-3, because the small ions have combined with the aerosol particles created by the combustion processes.

 

 

 

The total ion concentration, on the other hand, may hardly have changed.

 

But a most important quantity, the conductivity, has.

 

 

 

CONDUCTIVITY

 

Suppose an atmosphere has an ion concentration of n ions per unit volume with a mobility kj and each carrying a single elementary charge e. If an electric field E is established, a current will flow in the direction of the field with the density (current per unit area, Am-2), j, given by

 

 

 

j= e*n*k*E                        (5)

 

or

 

j= λ*E                      (6)

 

 

 

This is Ohm’s law (in differential form).

 

 

 

The quantity

 

λ = e*n*k                           (7)

 

 

 

is called the conductivity of the atmosphere (unit ohm-1m-1).

 

 

 

If the ions are distributed with respect to mobilities according to an function of frequencey f(k) in such a way that the concentration dn of ions with mobilities from k to k+dk is given by dn = f(k)*dk the conductivity is given by

 

 

 

λ = e * 0k*f(k)*dk           (8)

 

 

 

Now suppose the atmosphere has a concentration n of small ions with the mobility k1 and the same concentration n of large ions with the mobility k2, both species carrying an elementary charge e. The conductivity is then

 

 

 

λ = e*n*(k1 + k2)                (9)

 

 

 

Since k1 1000*k2, we see that if all the small ions are combining with neutral particles to form large ions, the conductivity will decrease with a factor of (almost) 1000, although the total ion concentration is still 2*n.

 

 

 

Both positive and negative ions contribute to the conductivity, but it should be kept in mind, that when ionized air is used for neutralizing static charges, positive ions can only neutralize negative charges and vice versa.

 

 

 

It is therefore convenient to introduce the polar conductivities, i.e. the conductivities due to positive and negative ions respectively.

 

          In case of an atmosphere with the concentration n+ and mobility k+ of positive ions and n- and k- of negative ions the polar conductivities are (with singly charged ions)

 

 

 

λ+ = e*n+*k+            (10)

 

and

 

λ- = e*n-*k-             (11)

 

 

 

λ+  and λ- are sometimes misleadingly called the positive and negative conductivity.

 

 

 

ION GENERATORS

 

Ion generators have been used extensively for many years in the textile, plastic and paper industry for neutralizing charges on fibers or sheet materials. The devices used are normally divided into passive, electrical and radioactive ionizers.

 

 

 

PASSIVE IONIZERS

 

A passive ionizer is in principle just a row of grounded (metal) points, placed a few centimetres from the charged material, Figure 6.

 

          The field from the charge will be deformed by the points and may here exceed the break down field strength, as given by Equation (3), resulting in a corona discharge. Ions of the opposite polarity will move towards the charged material and partly neutralize its charge.

 

 

Passive ionizers function equally well with positive and negative charges, but they suffer from the short-coming, that the corona discharge stops at a certain charge level, and so the rest charge is not neutralized. They are therefore primarily used where the problem is to remove large annoying charges, and where a minor rest charge is acceptable.

 

 

 

ELECTRICAL IONIZERS

 

In cases where a more or less complete neutralization of the charges is essential electrical ionizers are often used. Like the passive ionizers they consist of a row of points placed parallel with the charged material, but in this case the points are connected to a voltage source in order to make ionization possible even at low charge density on the material. The voltage source is often an ordinary transformer (about 5 kV), Fig. 7, which will alternately produce positive and negative ions in a fraction of each half period, determined by the voltage and the radius of the points. If the charged material is moving past the ionizer, the neutralization may thus be incomplete, and a DC-voltage may instead be used. If the charge on the material is always negative a voltage supply with a positive output may be used, and vice versa. But such a single polarity DC-ionizer is likely to overcompensate the neutralization and actually charge the material with the opposite polarity. This, however, can be avoided by the use of a double DC-ionizer, Figure 8, where alternate points are connected to a positive and negative voltage source.

 

 

 

 

RADIOACTIVE IONIZERS

 

In a radioactive ionizer the radioactive source is placed upon a base material and covered with an extremely thin protective layer, often made of gold. The rod-shaped ionizers are mounted in such a way, that the radiation is directed towards the space immediately in front of the charged material, Figure 9.

 

 

When one is dealing with relatively low levels of charging, or when the processing speed is slow, radioactive ionizers are very handy. They do not require electrical installations, and they function without electrical discharges, which in case of malfunctioning may cause ignition of inflammable atmospheres.

 

          The limitation to their use lies in the fact, that at  high charge levels, one has to use impractical high (radio)activities, or the discharging will take too long.

 

 

 

As far as the radiological hazard is concerned, it is safe to assume, that the direct – external – radiation from the ionizer is insignificant. If, however, the radioactive material, by accident or carelessness, is spread in the environment and for instance by evaporation becomes airborne, it may be inhaled, and the high energetic alpha radiation may eventually cause radiological damage to the respiratory tract, in the worst case initiating the growth of tumours. It should, however, be stressed, that with modern ionizers, the risk with proper handling and care is extremely low.

 

 

 

ION BLOWERS – WHOLE ROOM IONIZATION

 

The ionizers, described above, are all designed to be mounted immediately in front (or back) of the charged material.

 

 

In many cases, however, this arrangement is not practical or possible, and the ions have to be transported an appreciable distance from their site of production to the place of neutralization, usually aided by an air current.

 

          An ion-blower is essentially an electrical (usually DC-, single or double) or possibly radioactive ionizer encapsuled in a metal house (often forming the counter electrode) with an air orifice.

 

 

 

By blowing air past the region, where ionization takes place, Figure 10, it is possible to create an air jet with a relatively high ion-content. The jet may be directed towards hard-to-reach places or places where work operations prevent the mounting of a direct ionizer. Although it is difficult to maintain a high, even monopolar, ion concentration in a given air volume over long periods or distances because of diffusion, repulsion and combination of the ions, ion-blowers may, especially when dealing with sensitive components, offer the only practical solution.

 

          Some ion-blowers only produce ions of one polarity, but as already mentioned, this may, even when the polarity is correct, not lead to neutralization, but to re-charging of the objects. Hence ion-blowers should, as a rule, deliver a balanced, i.e. neutral, but highly ionized (conducting) air flow.

 

          Over the last few years a variation of the use of (normally) electrical ionizers have gained a growing popularity with the so-called whole room ionization.

 

          A series of point ionizers are mounted in the ceiling of the room and kept at such a voltage with respect to some properly mounted counter electrodes, that corona discharges take place and the ions (of both polarities) are disturbed in the room as a whole, preferably by diffusion or convection, to render air sufficiently conducting for neutralizing charges on work surfaces and elements.

 

 

 

MEASUREMENT OF IONIZATION

 

A thorough analysis of the ion population in a given atmosphere with respect to concentrations, polarities and mobilities is a very complicated and time consuming affair. And often a detailed knowledge of the ions and their concentrations is of less interest than just knowing what effect the running of an ionizing device has on the decay rate of charges in a given environment. And further, it may not even be practical possible, with any reasonable degree of accuracy, from a knowledge of the atmospheric electric parameters to predict the decay rate of a static charge, because the rate may depend strongly upon where the charge is located especially with respect to grounded surroundings, and upon whether or not the neutralizing charges are moved only because of an attraction from the charge to be neutralized or (partly) by an external electric field or a convectional air flow.

 

 

In practice, therefore, the charge neutralizing power of a ionizing device or installation is evaluated by the use of a so-called “charged plate”-system, shown principally in Figure 10. The voltage of the charged plate is deduced from the field from the plate measured by the field meter.

 

          The set-up is placed in the environment to be tested, the plate is charged to a given initial voltage, say 1000 or 5000 V, and the decay time to (usually) 10% of the initial voltage is measured. Further equilibrium voltage (off-set voltage) is measured, in order to evaluate the degree of balancing between two polarities. It should be stressed that the decay time measured in this way is different from (longer than) the theoretical neutralization time for free charges deduced from the conductivity of the air. It will also normally be different from the decay time of actual, “practical” charges, because the distribution of the electric flux is unlikely to be the same as with the test set-up. The charged plate system should therefore be considered as a device to compare the neutralizing ability of different ionizing systems, rather than an instrument to measure the neutralization time of practical charges.

 

 

 

ARE IONS GOOD FOR YOU ?

 

Atmospheric ions have often been claimed to have physiological, biological or hygienic properties.

 

          One of the most common claims is that air with an excess of small positive ions feels stuffy, while air with an excess of small negative ions feels fresh.

 

          No solid scientific study, however, supports this claim. Quite to the contrary heavy thunder air is rich in small negative ions, fresh mountain air in small positive ones !

 

          Negative ions are often, by manufacturers of monopolar ion generators, claimed to be charged oxygen molecules, while positive ions are said predominantly to attach to dust particles, soot and other unwanted airborne particles.

 

Thus negative ions should be beneficial to inhale, and positive not.

 

Such a statement is also without any kind of scientific basis.

 

          Buildings with so-called Sick Building Syndrome have been claimed to have a bad ion balance, by which is meant that the air has an excess of small positive ions, which should be caused by the presence of polymeric materials used as floor and wall coverings or by direct production from electronic equipment in the room.

 

          And by the kind of reasoning quoted above this should be bad.

 

The author has seen many recordings of lowered ion concentrations in closed rooms, and always because of high aerosol concentrations, but never, not one case, of dramatic imbalance between the two polarities. Unfortunately most reports on Sick Buildings are too superficial to truly expose this question.

 

          In passing it should also be mentioned, that the production of ions by electrical discharges is always accompanied by the production of ozone, a gas with probably the smallest gap between the lowest concentration that can be detected (by the nose) and the maximum permissible concentration. The ozone characteristics of a given ion source should therefore always be carefully checked.

 

          The whole topic of possible effects of ions (and electrical fields) on human beings has been treated in many papers. One of the best, On the Presence and Generation of AC and DC Electric Fields and Small Ions in Closed Rooms as a Function of Building Materials, Utilization, and Electrical Installation, is written by R. Reiter, in Journal of Geophysical Research, 90, D4, June 30, 1985, pp. 5936-5944).

 

          Dr. Reiter’s paper is highly recommended for anybody interested in the topic, and the following quote is to be happily countersigned by any scientist working with atmospheric electricity:

 

 

 

“Nearly all relevant assertations about harmful or beneficial effects of small ions fail to realize the fundamental elements of atmospheric electricity”.

 

 

 

It can, however, by no means be ruled out, that the atmosphere around us, interacts with us by electrical methods, and that the magnitude and distribution of electric charge has an influence on our well being and health.

 

          But such a relation has not yet been shown.

 

 

 

CONCLUSION

 

It is almost a hundred years since the existence of air ions was established. During the century passed, atmospheric electricity has changed from being a central area of scientific, basic research through a phase of quack metaphysics to become an extremely useful tool in many industries.

 

          Or, rather, all three phases coexist even today.

 

We can put ions to good use for a lot of purposes, but, in spite of frequent commercial and medical statements, some rather preposterous and ridiculous, we still don’t know if ions have any effect at all on human beings, and to be completely truthful, we don’t even really know the exact composition of an ordinary air ion.

 

 

 

 



 


 

 

 

 

 

 

 

Last modified on Thursday, 13 April 2017 16:52