Reduction of fine airborne particulates (PM 3) in a small city centre office, by altering electrostatic forces

Abstract

A two stage intervention study was carried out to establish the degree to which a newly developed, electrostatic air cleaning (EAC) system can improve indoor air quality (IAQ) by reducing the number of airborne fine particles. The IAQ and how employees in a city centre office (49 m 2) perceived it, was monitored from May until November 1998. The number of fine particles, PM 3 (0.3–3.0 μm); number of coarse particles, PM 7 (3.0–7.0 μm); number of small positive and negative air ions; relative humidity and temperature were recorded in and out of doors. To assess the employees’ perception of any changes in their work environment, a questionnaire was completed. Number of particles, relative humidity and temperature were also recorded in a nearby office, equipped with an identical air processor, where no interventions were made. The results from the first intervention (Stage 1), comparing number of airborne particles outdoors to indoors, gave a 19% reduction for PM 3 and a 67% reduction for PM 7 ( P<0.001). The reduction in PM 3 was inconsistent and not statistically significant ( P=0.3). The reduction in PM 7 from outdoors and the removal of PM 7 created indoors was achieved by optimizing the existing air moving equipment. The results from the second intervention (Stage 2 — with EAC units installed) comparing indoor to outdoor values, gave a further reduction in PM 3 of 21% ( P<0.001) and a further 3% reduction for PM 7 ( P>0.05). Therefore, at the end of Stage 2, the total reductions in particles from outdoors to indoors were 40% for PM 3 and 70% for PM 7 ( P<0.001). The Stage 2 results strongly suggest that electrostatic forces, created by the EAC unit(s) improved the removal of PM 3, with no further significant improvement in the reduction of PM 7. The questionnaire indicated an improvement in the IAQ, as perceived by the employees. The results suggest that the EAC system is effective in reducing PM 3 and thereby improving IAQ in an urban office.