Incidence and Apparent Health Significance of Brief Airborne Particle Excursions

The U.S. EPA has tightened control of fine particles primarily by limiting maximum 24 h average airborne concentrations. The present investigation used real-time monitoring to record short-term PM excursions and literature evaluation to determine whether PM levels reached in excursions might be health significant. Data recorded in Birmingham, AL, Penticton, British Columbia, and Zeebrugge, Belgium revealed numerous excursions, one reaching 2,000 mu g/M³. Toxicology and clinical studies involving brief exposures to particle levels in the range of observed excursions elicited adverse effects in both animals and humans. The area of lung surface developing lesions was elevated in rats breathing the same 4 h dose of aerosols when the 4 h average rate of aerosol delivery included a short-term (greater than or equal to 5 min) burst (greater than or equal to 50%) above the average dose rate. Elevations were observed with each of two aerosols tested. The magnitude of the effect was higher with one of the two aerosols, whose dose rate included four excursions rather than just one excursion. Symptom severity in asthmatics was associated with PM elevations, but the strength of the association depended upon the PM averaging time: the strength of the PM association with symptom severity increased as the PM averaging time varied from 24 h to 8 h to 1 h. Three hundred people were overcome after wind lofted particles into the air during a 4 day outdoor music festival in Queen Creek, AZ in April 1997. More research is necessary, but evidence presented here suggests that greater risk reduction might be achievable via controlling 1 h and 24 h PM averages than via tightening control of 24 h averages without controlling the 1 h average.