Project at a Glance

Title: Benefits of high efficiency filtration to children with asthma

Principal Investigator / Author(s): Bennett, Deborah

Contractor: UC Davis

Contract Number: 11-324

Research Program Area: Health & Exposure

Topic Areas: Health Effects of Air Pollution, Indoor Air Quality


One-hundred ninety-one asthmatic children 6-12 years old in regions with high outdoor air pollution (in and around Fresno and Riverside, CA), were enrolled in a randomized, placebo controlled, cross-over design trial to evaluate the effectiveness of high efficiency air filtration in reducing indoor exposures and asthma symptoms. The goal of the study was to recruit 200 children from 200 households. In total, 172 households were enrolled, 19 of which had two siblings with asthma who were both enrolled. These 19 pairs of siblings brought the total number of participants to 191. High efficiency filters were installed, utilizing the central system in 43 households and stand-alone air cleaners in 129 households. Of the 191 participants, 149 participants completed the study from 136 households.

Indoor air quality was significantly improved with filtration, with a 48% reduction in the geometric mean indoor PM0.2 and PM2.5 concentrations, and a smaller PM10 reduction (31%). Air quality improvements were greater with continuously operating stand-alone air cleaners than intermittent central-system filtration. Keeping windows closed and compliance with utilizing the intervention improved results. Indoor/outdoor reflectance values, a measurement that gives the fraction of black carbon particles of outdoor origin remaining in indoor air, was reduced by 77%. Greater reductions were observed for homes that did not open windows, and in homes 5 or more blocks from a major road or highway.

While there was no improvement in asthma symptoms, based on participant responses in the two week symptom diaries, there was a significant decrease in resource utilization (clinic visits, ER visits, and hospitalizations), particularly for severe asthmatics. Participants with air cleaners in their bedroom slept better if they also kept their bedroom door closed.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

Stay involved, sign up with CARB's Research Email Distribution List