In the reference condition, the concentration of particles was not reduced: cabinets with fans but with no deposition panels or ionizers were installed and operated in experiment 1EF, while in experiment 2EF unmodified electrostatic air cleaner cabinets continued to operate with the corona effect disabled.
The only study that directly tested this hypothesis was a recent field experiment in Sweden in which electrostatic air cleaners were operated or disabled in two pair of classrooms (Mattsson and Hygge 2005).
Electrostatic air cleaners are able to remove small airborne particles very effectively (Mattsson et al.
These were crossover experiments in pairs of classrooms in which electrostatic air cleaners were operated or disabled in the same week in each adjacent classroom.
Wilcoxon's matched-pairs signed-ranks test was used to analyze the main effects of running electrostatic air cleaners and filter condition when the assumption of normality was not valid (Wargocki and Wyon 2007a, 2007b).