Research conducted by Washington State University (1996) was undertaken to determine the impact of plants on the accumulation and deposition of indoor particulate matter. 

Two separate study rooms were selected within an air conditioned building. Interior plants occupied between 2-5% of total room volume and were added to or removed from the rooms on a random schedule. Over the duration of the study and on weekly intervals, particulate matter (PM) accumulation on horizontal surfaces was measured gravimetrically. Relative humidity and temperature were also monitored and data analyzed using an analysis of variance with treatment as the main effect.

The findings of the research indicate:

• Relative humidity was higher in rooms where plants were present
• Particulate matter deposition was unaffected by the presence or absence of plants
• Particulate matter accumulation was lower in rooms when plants were present

Moreover, these experiments determined that:

• A reduction of up to 20 % particulate matter accumulation was possible with the addition of interior plants