What Are We Breathing and How Can It Best Be Characterized?

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Inhalation Toxicolo gy, 12(Suppl ement 1):13- 14, 2000 Copy right © 2000 Taylo r & Francis WHAT ARE WE BREATHING AND HOW CAN IT BEST BE CHARACTERIZED? Robert F. Phalen D epartm ent of Community and Environmental M edicin e, University of California, Irvine, Irvine, California, USA The opening session of the colloquium, which addressed the issues of defining and characterizing relevant PM exposures, consisted of introductory and summary talks, po ster viewing, and a discussion between the audience and an expert panel. The platform presentations and expert panel members' comm ents tended to point to areas in need of new research, whil e the 50 posters documented recent advances in knowledge, This commentary high- lights some of the information that was presented, Several speakers emphasized that under standing personal exposures is a key to uncovering who might be affected by PM inhalation, under what circum- stances they might be affected, and what pollutant sources (or atmospheric chemical processes) might be producing the effects, Jack Spengler (Boston) commented that the average person spends 87% of his or her time indoors, that air conditioning can greatly reduce the penetration of outdoor PM·into the indoor air, and that as the number of people in a room increases, so do the pollutant levels, Also, O j-generating air cleaners can greatly increase the ultrafine particle count indoors. He pointed to several areas in need of further research: chemical characterization of indoor PM; the toxicology of indoor PM; emi ssion source characteristics; infiltration and turnover rates for air con- taminants indoors; and how human activities modify indoor PM expo sures. Petros Koutraki s (Boston) stated that the perso nal cloud is largely composed of coarse-mode (>2.5 urn aerodynamic diameter) particles, and that the great- est differences in outdoor versus indoor PM is expected in the wintertime. Koutrakis called for additional research on defining actual exposures (both personal and community), better chemical and temporal characterizations of exposures, and uncovering the factors that produce subject variability in PM exposures; such research will require improvements in methodology. Harriet Burge (Boston) emphasized the serious lack of understanding of exposures to biological aerosols. She commented that pollen and spore levels are as- sociated with asthma, hospitalizations, and mo rtality. Burge remarked that a single inhaled ragweed pollen grain can produce symptoms in a sensitive per- son. Judith Chow (Reno, NV) indicated that there is also a need to improve the consistency among the many PM sampling methods that are commonly Add ress cor respondence to D r. Rob ert F. Phalen, Departm ent o f Co mmunity and Environm ent al M edicin e, Universit y o f California , Irvine, Irvi ne, CA 92697-1825, USA. E-mail: rfphalen@uci.edu