Controlled Human Exposures to Concentrated Ambient Fine Particles in Metropolitan Los Angeles: Methodology and Preliminary Health-Effect Findings

Abstract

We installed a Harvard particle concentrator with PM2.5 size-selective inlet and two virtual impactor stages, in a movable human exposure laboratory located in metropolitan Los Angeles, where ambient PM2.5 is unusually high. The exposure chamber, a modified body Plethysmograph of ~2000 L volume, operated at flow near 200 L/min and pressure near 25 cm H₂O below atmospheric. The concentrator usually delivered seven to nine times the ambient concentration of PM2.5. When necessary, part of its output was diverted through a HEPA filter to control the exposure concentration. Occasionally the concentration factor decreased due to rapid fouling of impactor slits under humid and/or highly polluted ambient conditions. Initial tests with an investigator (healthy male, age 53 yr) at rest in the chamber showed no untoward effects except rare transient mild substernal irritation, brief mild middle ear discomfort from pressure changes upon starting or stopping the concentrator, and occasional ectopic heartbeats (which also occurred apart from the exposures). Maximum in-chamber concentrations exceeded 300 μg/m³, 30-min average. Subsequently, healthy adult volunteers (2 female, 2 male, age 19–41 yr) completed 2-h resting exposures to ambient PM2.5 at 2-h average concentrations of 148 to 246 μ³ , and similar studies with HEPA-filtered air (control condition). No medically significant changes in lung function, symptoms, arterial O₂ saturation, or Holter electrocardiograms (recorded during and for 22 h after exposure in 3 subjects) were observed. We conclude that exposures to concentrated ambient particles are operationally and ethically feasible in metropolitan Los Angeles. Larger scale studies of healthy volunteers, and then of volunteers with respiratory or cardiovascular disease, are planned.