Many claims have been made about the effects of air ions on health but little 'scientifically acceptable' research on ions has actually been carried out. There is even controversy over the exact nature of ions, although they are usually described as positively or negatively charged forms of the molecules that make up the atmosphere.
It seems that all living things need ions to survive. Scientists in the USSR tried to raise small animals in air containing no ions at all and found that all the mice, rats, guinea-pigs, rabbits, etc. died within a few days. Similar experiments on plants produced stunted growth. One of the few controlled experiments carried out on humans in the UK showed that increasing the number of negative ions in a computer-operating area reduced complaints of headache, nausea and dizziness, and resulted in a significant improvement in the rating of environmental quality. The workers also felt more comfortable and alert. Effects were most marked for those on the night shift (Hawkins 1984). Other workers have failed to reproduce these findings.
The number of negative ions in the atmosphere seems to be more important than the number of positive ions. Research worldwide has associated lack of negative ions with a range of diseases including thrombosis, haemorrhage, asthma and bronchial diseases, difficulty in breathing, aching joints, migraines, insomnia and increased susceptibility to infections. It has also been connected with depression, lethargy, anxiety, mental hospital admissions, suicides and crimes of violence. In contrast, an excess of negative ions is reputed to be associated with feelings of calmness, alertness and well-being, with quicker recovery from exhausting exercise, more appetite, sounder sleep, fewer bodily aches and pains, and fewer respiratory complaints.
Not everyone is sensitive to changes in air ion concentration: about 25 per cent of people notice no difference when the proportion of positive to negative ions is changed. Women seem to be more sensitive to ion depletion than men and respond more favourably to an ion-enriched environment (Hawkins 1984). Negative ions seem to become less effective as the ambient temperature increases above 22"C and at high relative humidities.
The typical air-conditioned office in the city has only 50 negative ions per millilitre of air (and 150 positive ions) compared with 1000 negative ions (and 1200 positive ions) in the same volume of clean, outdoor, country air. Hawkins (1984) gives the reasons for low air ion levels indoors as:
Ducted air conditioning. Metal ducting attracts charged particles so that ions are stripped out of the air as it passes through the ductwork. (Electrostatic filters would similarly reduce ion levels.)
Static electricity. In an air-conditioned building, especially one with low humidity, static charges build up on carpets, furniture, wall fabrics, workers' clothing and, particularly, on electrical equipment such as VDU screens. Ions in the room are then attracted to these static charges.
Smoke and contamination. Smoke and dust particles act as a sponge, mopping up ions.
High density of individuals. Each person removes ions from the air while breathing and each carries an amount of static electricity.
No-one knows how or why air ions may exert their effects. Many of the symptoms of negative ion depletion are similar to the effects of stress on the body, so it may be that the body's hormonal system is affected.
So how can the effects of low levels of negative ions be counteracted? It is clear that ion depletion can be minimised by taking steps to reduce the amount of static electricity in the environment, using natural rather than synthetic fibres wherever possible, making sure that all VDUs and other equipment likely to build up a static charge are properly earthed, controlling humidity and temperature, removing pollutants and dust at source, and ensuring that offices are not overcrowded. Negative ionisers help to clean the air by precipitating dust, fibres and particles out of the atmosphere - as can be seen by the enormous amount of dirt streaking the area that immediately surrounds the ioniser. So, if ionisers are to be introduced as a means of giving workers individual control over their immediate working environment, ensure that proper cleaning arrangements are made to cope with the resulting dirt. This may involve the cleaners working extra time.