ARB Research Seminar

This page updated April 14, 2015

Reducing Air Pollution Exposure in Passenger Vehicles and School Buses

Photo of Yifang Zhu, Ph.D.

Yifang Zhu, Ph.D., UCLA Fielding School of Public Health, University of California, Los Angeles

April 21, 2015
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


Exposures to vehicle-emitted PM₂.₅, black carbon (BC), and ultrafine particles (UFPs), have been associated with adverse health effects. As a potential strategy to mitigate in-cabin exposure, we developed a novel high efficiency cabin air (HECA) filter for passenger vehicles and an on-board HECA filtration system for school buses.

Their performance was evaluated in 12 passenger vehicles and 6 school buses, respectively. UFP number concentration and size distribution as well as BC and PM₂.₅ levels were concurrently monitored inside and outside of each vehicle under three driving conditions: stationary, on local roadways, and on freeways. For passenger vehicles, data were collected with no filter, the in-use original equipment manufacturer (OEM) filter, and two prototypes of HECA filters (i.e., HECA A and B filters). For school buses, data were collected with and without operating the filtration system equipped with HECA B filters. For passenger vehicles, the HECA B filters offered in-cabin concentration reductions of 90 8% for UFPs on average across all driving conditions, which is much higher than the reductions seen with (or achieved by) the OEM filters (50 11% on average). Similarly, the HECA B filters offered an 81 15% reduction for BC and 66 28% for PM₂.₅ across all driving conditions. In comparison, across all driving conditions, the in-use OEM filters only provided 31 17% and 29 20% reduction for BC and PM₂.₅, respectively. For school buses, across all driving conditions, in-cabin UFP and BC levels were reduced by 88 6% and 84 5% on average, respectively, when the on-board HECA filtration system was operating. The application of this technology in passenger vehicles also kept in-cabin CO2 concentration below 1,000 ppm under outdoor air mode. In-cabin PM₂.₅ was also reduced from approximately 35 μg/m³ to 10 μg/m³.

This proof-of-concept study concludes that the HECA technology can significantly reduce human exposures to UFPs, BC, and PM₂.₅ in passenger vehicles and school buses. Practical application of the HECA filter, however, requires long-term evaluations under a broader range of vehicle models and driving conditions.

Speaker Biography

Yifang Zhu, Ph.D., is an Associate Professor of the Environmental Health Sciences Department, UCLA Fielding School of Public Health, University of California, Los Angeles (UCLA). Dr. Zhu's research interest is primarily in the field of air pollution, environmental exposure assessment, and aerosol science and technology. Specifically, she is interested in quantitative exposure/risk assessments on ultrafine particles from various indoor and outdoor sources. Dr. Zhu's current research focuses on measuring and modeling ultrafine particle emissions, transport, and transformation on and near roadways as well as in various indoor environments. Dr. Zhu's scholarship and creativity has been recognized by several national awards, including the Walter A. Rosenblith New Investigator Award from the Health Effects Institute in 2007, the Faculty Early Career Development (CAREER) Award from the National Science Foundation in 2009, and the Haagen-Smit Prize from Atmosphere Environment in 2011. Dr. Zhu was appointed to the California Air Resource Board's Research Screening Committee in January 2014. Dr. Zhu received her Ph.D. in Environmental Health Sciences from UCLA in 2003.

For a complete listing of the ARB Research Seminars and the related documentation
for the seminars please view the Main Seminars web page