ABSTRACT. The U.S. EPA has tightened control of ® ne 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 signi® cant. Data recorded in Birmingh am, AL, Penticton, British Columbia, and Zeebrugge, Belgium revealed numerous excursions, one reaching 2,000 m g r r r r r M 3 . Toxicology and clinical studies involving brief exposures to particle levels in the ran ge 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 G 5 min burst G 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, wh ose 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 an d 24 h PM aver ages th an via tightening control of 24 h averages without controlling the 1 h average.

Ammonia is present in agriculture and commerce in many if not most communities. This report evaluates the toxic potency of ammonia, based on three types of data: anecdotal data, in some cases predating World War 1, reconstructions of contemporary industrial accidents, and animal bioassays. Standards and guidelines for human exposure have been driven largely by the anecdotal data, suggesting that ammonia at 5,000-10,000 parts per million, volume/volume (ppm-v), might be lethal within 5-10 min. However, contemporary accident reconstructions suggest that ammonia lethality requires higher concentrations. For example, 33,737 ppm-v was a 5-min zero-mortality value in a major ammonia release in 1973 in South Africa. Comparisons of secondary reports of ammonia lethality with original sources revealed discrepancies in contemporary sources, apparently resulting from failure to examine old documents or accurately translate foreign documents. The present investigation revealed that contemporary accident reconstructions yield ammonia lethality levels comparable to those in dozens of reports of animal bioassays, after adjustment of concentrations to human equivalent concentrations via U.S. Environmental Protection Agency (EPA) procedures. Ammonia levels potentially causing irreversible injury or impairing the ability of exposed people to escape from further exposure or from coincident perils similarly have been biased downwardly in contemporary sources. The EPA has identified ammonia as one of 366 extremely hazardous substances subject to community right-to-know provisions of the Superfund Act and emergency planning provisions of the Clean Air Act. The Clean Air Act defines emergency planning zones (EPZs) around industrial facilities exceeding a threshold quantity of ammonia on-site. This study suggests that EPZ areas around ammonia facilities can be reduced, thereby also reducing emergency planning costs, which will vary roughly with the EPZ radius squared. Images Figure 1 Figure 2

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