Epidemiological data indicate that increased small positive air ionization due to changing weather conditions is associated with increases in industrial and automobile accidents, suicide, and crime as well as depression, irritability, and interference with central nervous system (CNS) function. Laboratory research is less consistent, with several studies reporting no effects on mood or performance indicative of CNS disturbance. We have designed an experiment that begins to resolve these contradictory data by examining individual differences in response to small positive air ions. Analysis of these data indicates that whereas mood changes were present for most subjects when exposed to positive ions, assessment of individual differences in susceptibility was essential for detecting effects on performance and physiological activation. For most subjects, mood changes induced by ion exposure were characterized by increased tension and irritability. For susceptible (ion-sensitive) subjects, skin conductance measures showed depressed activation and reaction time increased during exposure to ions. For non-sensitive subjects, skin conductance measures revealed increased activation, with no effects of ions on reaction time.
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