ARB Research Seminar

This page updated June 19, 2013

Understanding Ultrafine Particles Indoors

William W. Nazaroff, Ph.D., Civil Engineering Department, University of California, Berkeley

February 02, 2010
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


Field monitoring of ultrafine particles and copollutants was undertaken at seven houses and six classrooms in the East Bay region near San Francisco, California. At each site, time-resolved measurements were made indoors and outdoors of particle number (PN) concentration in addition to nitric oxide, ozone, carbon dioxide and carbon monoxide. Data were also acquired through the use of questionnaires (houses), observation (classrooms), and temperature and proximity sensors. The information from each site were analyzed to characterize (1) indoor and outdoor PN concentrations; (2) key factors that influence indoor PN concentrations; and (3) the exposure of building occupants to indoor PN and its determinants.

During observational monitoring, the time-averaged PN concentrations from the primary indoor monitor varied across the seven house sites from 3.7 x 10³ particles per cm³ to 28 x 10³ particles per cm³ (averaging 14.5 x 10³ particles per cm³). The corresponding outdoor concentrations ranged from 5.5 x 10³ to 23 x 10³ particles per cm³ (averaging 15 x 10³ particles per cm³). For five classroom sites (excluding one at which overnight outdoor data were incomplete), the time-average indoor concentrations ranged from 3.2 x 10³ to 10.5 x 10³ particles per cm³ (averaging 6.9 x 10³ particles per cm³); the corresponding outdoor concentrations ranged from 9.7 x 10³ to 16 x 10³ particles per cm³ (averaging 13 x 10³ particles per cm³).

Overall, the results inform the interplay among building factors, human occupancy, and pollutant dynamics as they influence concentrations of and exposures to ultrafine particles in the studied houses and classrooms. Particle levels in classrooms and in houses were much higher when occupied than when vacant. In houses, important contributions to PN levels were attributable to both outdoor particles and indoor emission sources such as cooking (both with natural gas and electricity) and natural gas furnace use. In schools, the dominant PN source was outdoor air and indoor levels were significantly influenced by time-varying ventilation conditions. Daily average PN exposures per person were much higher in houses than in schools.

Speaker Biography

William W. Nazaroff, Ph.D., is Daniel Tellep Distinguished Professor and Vice-Chair for Academic Affairs in the Civil and Environmental Engineering Department, University of California, Berkeley. Dr. Nazaroff joined the faculty there two decades ago after receiving his education in Physics (BA, UC Berkeley, 1978), Electrical Engineering and Computer Science (MEng, UC Berkeley, 1980), and Environmental Engineering Science (PhD, Caltech, 1989). Professor Nazaroff's research group focuses on the physical science and engineering aspects of air pollution exposure, with a special emphasis on indoor environments. Dr. Nazaroff served on ARB's Research Screening Committee (2000-2002). At present, he serves as Vice-President Elect of the American Association for Aerosol Research (AAAR), as coeditor of Indoor Air, and as Vice President of the Academy of Fellows of the International Society of Indoor Air Quality and Climate. Dr. Nazaroff is author and coauthor of over 120 research articles published in archival journals and coauthor (with L Alvarez-Cohen) of the textbook, Environmental Engineering Science (Wiley, 2001).

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