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Table 2 Air ion exposure assessment, psychological measures, and study findings

From: Air ions and mood outcomes: a review and meta-analysis

Author and year Air ion exposure (Duration) Ion concentration Metrics used for mental health outcomes Primary findings
Silverman and Kornblueh 1957[27]a,b Negative air ion (30 minutes) Not reported Human electroencephalogram Decrease in alpha frequency in most subjects; half of the subjects reported relaxation and sleepiness with ionization (slightly more frequent for (−) than (+) ion exposure); one consistent finding was a decrease in alpha frequency during negative or positive ionization (or both) in all but two subjects. Findings reported as “transient.”
Positive air ion (30 minutes) Activations by hyperventilation, apnea, photic stimulation and sleep (natural)
McGurk, 1959[17]c Negative air ion (5 hours) 8.0 × 103 ions/cm3 Self-reported feelings of comfort, ease by which subjects worked on a cognitive task, and reactions to the test room atmosphere Regarding negative ionization, a significant percent of subjects appeared to detect ionization condition despite blinding and reported more pleasant feelings.
Positive air ion (2 hours) Regarding positive ionization, subjects reported more unpleasant feelings.
Yaglou, 1961[19]b Negative air ion (1–2 hours) 5,000 to 10,000 ions/cm3 air Self-reported impressions (indifference, relaxation, air freshness, headache, respiratory irritation, restlessness) Subjectively, positive air ions seemed to increase the incidence of upper respiratory irritation in the winter, while negative air ions had little or no effect on the quality of air.
Positive air ion (1–2 hours) 5% of subjects reported feeling relaxed when exposed to positive air ions; 17% reported feeling relaxed when exposed to negative air ions; and 21% of subjects reported feeling relaxed under control conditions
Yaglou, 1961[19]b Negative air ion (1–2 hours) 105-106 ions/cm3 air Self-reported impressions (indifference, relaxation, air freshness, headache, respiratory irritation, restlessness) Subjectively, negative air ions did not alleviate joint symptoms, while positive air ions seemed to make the symptoms worse; a higher frequency of patients reported feeling relaxed or sleepy, or both when exposed to negative versus positive air ions
Positive air ion (1–2 hours)
Assael et al., 1974[11]b Negative air ion (45 minutes) 3.5 × 105 ions/cm3 EEG parameters: Decrease in alpha frequency manifestation of general relaxation induced by negative air ions. Increase of amplitude interpreted as improvement of perception and apperception. Subjectively, all patients experienced initial relaxation followed by alertness connected with moving of alpha-waves from occipital to frontal areas.
frequency (Hz)
amplitude (μV)
spreading of alpha waves area
synchronization of right and left hemispheres
Self-reported relaxation, alertness, working capacity, relief
Albrechtsen et al., 1978[37]b,c Negative air ion (Experiment I: 8 hours; Experiment II: 15 minutes) Positive air ion (Experiment I: 8 hours; Experiment II: 15 minutes) 300-9,000 ions/cm3 Mental performance: No significant effects of positive or negative air ions found.
number of tasks per hour
Subjective voting based on % scale:
extent of exertion
perception on air quality
perception of tasks
current feeling (sleepy vs. alert)
Charry and Hawkinshire, 1981[15]a Positive air ion (1.5 hours ) Positive air ions: 2.0-3.0 × 104 ions/cm3 Mood Adjective Check List For most subjects, mood changes induced by air ion exposure characterized by increased tension and irritability.
Ambient condition (contained both) (1.5 hours) Ambient: 3.0 × 102 ions/cm3 Sharav Questionnaire (mood)
Hawkins, 1981[38]b, c Negative air ion (Weeks 5 to 12- on continuously) Negative air ion: 2.0-3.5 × 103 ions/cm3 Personal ratings of thermal comfort, stuffiness, alertness, well-being Negative air ion exposure associated with higher subjective ratings of alertness, atmospheric freshness, environmental/personal warmth, and a reduction in the overall complaint rate by 50%. Night-shift working was associated with discomfort and ill-health. Positive air ion effects were not explicitly discussed.
Positive air ion (Weeks 5 to 12- on continuously) Positive air ion: 50–125 ions/cm3 air
Tom et al., 1981[34]a,b Negative air ion (15 minutes) Negative air ion: 16,160 ions/cm3 Likert scale survey for psychological state (difficulty of concentration, energetic, mood state, sociable, relaxed) Subjects reported being more energetic and finding it easier to concentrate under the experimental condition than the control condition. Negative air ion exposure had a positive effect on certain aspects of human performance and mood.
Control (natural environment): 204.4 ions/cm3
Buckalew and Rizzuto, 1982[12]a,b Negative air ion (6 hours) Not reported Taylor Manifest Anxiety Scale (TMAS) Mood index data showed significant changes in the subjective perception of both physiological state (relaxation increased) and psychological state (irritability, depression, and tenseness decreased while calmness and stimulation increased).
Self-report Mood Index
Dantzler et al., 1983[25]a Negative air ion (6 hours) Negative and positive air ions: 60,000-110,000 ions/cm3 Sharav Questionnaires 1 and 2 Mood Adjective Check List Patients’ mood did not differ significantly between the two ion exposures.
Positive air ion (6 hours)
Baron et al., 1985[28]a Negative air ion (20 minutes) Ambient condition: 2.0-3.0 × 102 ions/cm3 Self-reported affect (Profile of Mood States survey) Exposure to moderate or high levels of negative air ions significantly enhanced aggression by Type A subjects, but not among others. Negative air ions produced positive shifts in reported moods in the absence of provocation, but negative shifts in moods in the presence of provocation.
Moderate condition: 4 × 104 ions/cm3 Aggression measured by mean level of heat selected by subjects on each of the 20 occasions when the red light appeared
High condition: 7.0-8.0 × 104 ions/cm3 Memory measured by the number of traits and the number of behaviors subjects could recall about the accomplice
Deleanu and Stamatiu, 1985[29]a,b,d Negative aeroionotherapy (daily treatment of 15–50 minutes for 10–30 days) 1-1.5 × 104 ions/cm3 Amelioration of asthenia, depressive reactions, anxiety, excitability and irascibility, cephalea, insomnia, and general disposition in patients with various psychiatric disorders In most treated patients, a diminution or even the disappearance of the target symptoms was obtained (asthenia, depressive reactions, anxiety, irascibility, cephalea, insomnia, and general disposition).
Gianinni et al., 1986[16]a Negative air ion (20 minutes) Negative air ion: not reported Brief Psychiatric Rating Scale Cations were found to increase anxiety, excitement, and suspicion. Anions reversed the effects of cations and, in addition, reduced suspicion and excitement to levels below those occurring before cationization.
Positive air ion (20 minutes)
Positive air ion: 2.9 × 103 ions/cm3
Gianinni et al., 1986/87[30]a Positive air ion (2 hours) 2,050-2,300 ions/cm3 Brief Psychiatric Rating Scale Symptoms of anxiety and excitement significantly increased. During the time of exposure, serum serotonin levels also increased significantly.
Finnegan et al., 1987[40]c Negative air ion (6–8 weeks) 1.84 × 103 ions/cm3 Personal comfort rating No significant effect on personal comfort found. Effects on symptoms were non-significant except for URTI and nausea in the high negative air ion period.
Hedge and Collis, 1987[18]a Negative air ion (7 hours) 2 × 104 ions/cm3 Mood Adjective Check List Evidence for beneficial effects of negative air ions on mood and performance could not be demonstrated.
Two cognitive tasks:
naming 24 different colors printed on card
Stroop Colour Word test
Lips et al., 1987[13]b,c Negative air ion Weeks 2 and 4 - on continuously; Week 3 - mornings only 5 × 104 ions/cm3 10 linear scales (rated 0 to 10) on which each subject was asked to assess his or her well-being and the quality of the environment After their exposure to enhanced negative air-ion concentrations, the subjects' assessments of both their own well-being and the quality of the environment improved significantly: neither harmful effects of exposure to enhanced levels of negative air ions nor changes in perceived thermal comfort were detected.
Misiaszek et al., 1987[14]a,b Negative air ion Phase I: 1 hour; Phase II: 1.5 hours Phase I: 40,000-60,000 small, 50–1000 medium, 50–4,000 large ions/cm3 State Trait Anxiety Inventory and Inpatient Multidimensional Psychiatric Scale Phase I: All subjects fell to sleep, reported being calm afterwards; manic behavior reappeared 5–10 minutes after treatment
Phase II: 3/4 subjects fell to sleep, 1 subject appeared less agitated; manic behavior reappeared 5–10 minutes after treatment
Phase II: 50,000-70,000 small, 50–3,200 medium, 50–7,000 large ions/cm3
Reilly and Stevenson, 1993[33]a Negative air ion (30 minutes pre-test + 40 minutes during test) 1.72 × 105 ions/cm3 Measurements were made of state anxiety according to Spielberger et al. (1970) There was no significant effect of air ions on state anxiety pre-or post-exercise or on the perception of effort.
Terman and Terman, 1995[6]d Negative air ion (30 minute sessions for 20 days) Low density: 1.0 × 104 ions/cm3 SIGH – SAD The severity of depressive symptoms decreased selectively for the group receiving high-density treatment. When a remission criterion of 50% or greater reduction in symptom frequency/severity was used, 58% of subjects responded to high-density treatment while 15% responded to low-density treatment.
Clinical Global Impressions Scale
High density: 2.7 × 106 ions/cm3
Watanabe et al., 1997[35]a,c Negative air ion (10 minutes) 2.0 × 104 ions/cm3 Self-reported feelings of temperature, pleasantness, fatigue, and sweating There were no differences in the moods of these persons or changes in their blood pressures between the two saunas.
Terman et al., 1998[8]b,d Negative air ion (30 minutes per day for 10–14 days) Low density: 1.0 × 104 ions/cm3High density: 2.7 × 106 ions/cm3 SIGH – SADSelf-rating version of the SIGH-SADSleep patterns Improved depression rating of 42-50% and 20-40% remission rate. Described as a "small effect" in period 1 and "large effect" in period 2. Analysis of depression scale percentage change scores showed low-density air ion response to be inferior to all other groups, with no other group differences. Sleep measures subjects given morning light awakened 0.62 ± 0.62 hours earlier than at baseline; negative air ions, 0.41 ± 0.37 hours earlier; and evening light, 0.09 ± 0.58 hours earlier.
Nakane et al., 2002[10]a Negative air ion (40 minutes during task or 30 minutes post-task) 5.5-7.3 × 103 ions/cm3 Japanese version of the State-Trait Anxiety Inventory, Anxiety StateSalivary cortisol and chromogranin A-like immunoreactivityTask performance The increase in the CgA-like IR level was attenuated by the exposure to negative air ions during the task. The exposure to air ions during the recovery period following the task was effective for rapidly decreasing the CgA-like IR level that had increased after the task. These effects by negative air ions were also observed using STAI-S. Task performance was slightly but significantly improved by the presence of negative air ions.
Iwama et al., 2004a[39]b Negative ion (not reported) 3000 parts/cm3f Degree of tension: 1 = relaxed; 2 = normal tension; 3 = mild tension; 4 = moderate tension; and 5 = severe tension Degree of tension decreased significantly and more rapidly in the negative ion-rich environment.
Goel et al., 2005[22]b,d Negative ion (1 hour upon wakening for 5 weeks) Low density: 1.7 × 1011 ions/s [1 × 104 ions/cm3]e SIGH – SAD SIGH-SAD score improvement was 51.1% for high-density ions v. 17.0% for low-density ions. Remission rates were 50% and 0%, respectively.
High density: 4.5 × 1014 ions/s [2.7 × 107 ions/cm3]e Evening saliva samples obtained before and after treatment for ascertainment of circadian melatonin rhythm phase
Goel and Etwaroo, 2006[5]a,b,d Negative ion (30 minutes for three consecutive evenings) Low density: 1.7 × 1011 ions/s [1 × 104 ions/cm3]eHigh density: 4.5 × 1014 ions/s [2.7 × 107 ions/cm3]e BDI The three active stimuli (bright light, auditory stimuli, or high-density negative ion exposure), but not the low-density placebo, reduced depression, total mood disturbance and/or anger within 15–30 min.
The Profile of Mood
States Questionnaire
The Karolinska Sleepiness Scale
Likert scales assessed four aspects of stimulus perception using a 7-point scale. Subjects rated stimulus hedonics and intensity, as well as its effects on mood and on alertness
Terman and Terman, 2006[7]b,d Negative ion (93 minutes before waking up) Low density: 1.7 × 1011 ions/s [1 x 104 ions/cm3]e SIGH – SAD Post-treatment improvement results were high-density ions, 47.9%; and low-density ions, 22.7% (significantly different).
High density: 4.5 × 1014 ions/s [2.7 x 107 ions/cm3]e Emergence or exacerbation of depression, sleep, appetite/weight, headache
Gianinni et al., 2007[26]a Negative ion (1 hour) 3 × 103 ions/cm3 Brief Psychiatric Rating Scale A significant anti-manic effect was observed: total rating scores declined with anion treatment.
Malcolm et al., 2009[32]a,b Negative ion (30 minutes pre-test and 60 minutes during test) Not reported Subjective state measured by six visual analogue scales for happiness, sadness, hostility, alertness, anxiety and calmness. Association between BDI score and treatment; increased recall and recognition of positive terms versus negative terms; findings indicate that HDNI treatment produces a positive bias in emotional recall and recognition.
The emotional test battery consisted of an emotional categorization task with surprise emotional recall and recognition, a facial expression recognition test, and a dot-probe task of attention with masked and unmasked conditions.
Flory et al., 2010[4]d Negative ion (30 minutes for 12 days) Low density: 4.0 × 103 ions/cm3 SIGH – SAD–Self Rating: Subjects in all four groups showed significant score decreases on the SIGH-SAD-SR and on the BDI. For raw scale scores, neither main effects of treatment nor interactions between treatment and time were significant. When remission outcome criteria were used, exposure to high-density negative ions was more effective than either of the two placebo conditions, although the difference was not significant.
High density: ≥ 2.0 × 106 ions/cm3 BDI
Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) criteria for SAD
Malik et al., 2010[9]a Negative ion (2 hours) >1,000,000 counts/cm3 Self-reported computer-oriented stress, physiological and psychological stress A significant decline in computer-oriented stress and psychological stress was noticed post-computer operations in presence of negative ions.
Dauphinais et al., 2012[24]d Negative ion (7.5 min/day or 15 min/day if tolerable for 8 weeks) 1.7 × 1011 ions/s [1 × 104 ions/cm3]e SIGH-SAD No significant difference in SIGH-SAD scores between light therapy and low-density negative ion groups at study end or in the proportions of responders or remitters in these groups.
Harmer et al., 2012[31]a,b,d Negative ion (30 minutes pre-test and 60 minutes during test) Not reported Subjective state measured by six visual analogue scales (happiness, surprise, sadness, fear, anger, and disgust), BDI, and State-Trait Inventory No effect on anxiety, depression (BDI), alertness, and recall of emotional words. HDNI treatment decreased recognition of faces showing disgust and increased recognition of happy faces, and increased recognition of and vigilance to positive words. HDNI increased recognition memory of positive words only in the SAD group. The findings indicate that HDNI treatment produces a positive bias in emotional recall and recognition.
    The emotional test battery consisted of an emotional categorization task with surprise emotional recall and recognition, a facial expression recognition test, and a dot-probe task of attention with masked and unmasked conditions.  
  1. aActivation, anxiety, mood.
  2. bRelaxation and sleep.
  3. cPersonal comfort rating.
  4. dDepression.
  5. eIons/s converted to ions/cm3 for ionizers used in this laboratory based on Terman et al. [8].
  6. fIon concentration in ion/cm3 based upon Iwama et al. [41].
  7. BDI beck depression inventory; CgA-like IR chromogranin A-like immunoreacitivity; HDNI high-density negative ions; SR self-rating; STAI-S state trait anxiety inventory scale; SIGH-SAD structured interview guide for the hamilton depression rating scale, seasonal affective disorder.