Health Risks and Particle Monitoring: New Technologies to Meet Emerging Needs. Robert A. Michaels, RAM TRAC Corporation*
Abstract of a paper presented at the 14th Annual Meeting of the American Association for Aerosol Research (AAAR), Pittsburgh, Pennsylvania, October 9-13, 1995; in AAAR '95 Abstracts, p. 338, 1995.
The U. S. EPA is reviewing the National Ambient Air Quality Standard for particulate matter. The present standard limits particles within a diameter of 10 microns to a time-weighted average mass limit of 150 µg/M3 of air over 24 hours (and 50 µg/M3 annually). It is based primarily upon epidemiological associations of particle elevations during air pollution episodes with elevated human mortality and morbidity in multiple communities. However, problems with these associations motivated the present investigation of available toxicological data to reevaluate the time frames over which particles may exert adverse health effects and the availability of technologies to fill identified short-term particle mass data gaps.
Associations between health effects and 24-hour particle levels are weak. Eliminating confounding factors as alternative causes is impossible using the database generated by particle monitoring standards to date. Moreover, toxicology provides no known mechanism by which low airborne particle levels may cause the effects with which they are associated. Consequently, toxicological literature was investigated to determine whether higher particle levels, surely present at some locations over brief portions of a 24-hour averaging period, might cause adverse effects. This investigation revealed, for example, significant decrements in airway conductance occurring within 16 minutes of exposure of asthmatic volunteers to sulfuric acid aerosol at 450 µg/M3. A 24-hour average particle level within the 150 µg/M3 standard is consistent with excursions averaging 450 µg/M3 over a period of say, 16 minutes.
Observed excess daily morbidity and mortality may be toxicologically attributable to cardiopulmonary stress induced by particles and/or associated substances, Thus, known mechanisms may explain observed effects if viewed over an appropriately short time frame. However, the standard requires averaging over at least 24 hours, weakening associations which may be causal. Thus, a data gap exists, prompting investigation of the availability of technologies to quantify particle excursions with a time resolution of one hour or less. Two proven technologiesinertial and beta attenuationwere identified.
The cost of complying with particle regulations is large. Both monitoring technologies identified above are automated, whereas the 24-hour F-PA method is labor intensive. Thus, a one-hour mass limit may eliminate the need to strengthen more burdensome longer-term mass limits while being (1) more effective at protecting health, (2) justified by available data, and (3) economically feasible.