Morphological and Chemical Characteristics of the Submicron Atmospheric Aerosol: Implication for StandardsEPA Grant Number: R826232
Title: Morphological and Chemical Characteristics of the Submicron Atmospheric Aerosol: Implication for Standards
Investigators: Friedlander, Sheldon
Institution: University of California - Los Angeles
EPA Project Officer: Shapiro, Paul
Project Period: January 2, 1998 through January 31, 2001
Project Amount: $345,247
RFA: Ambient Air Quality (1997) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objectives/Hypotheses: Current plans to set a revised particulate ambient air quality standard are based largely on epidemiological data that show an association between adverse health effects and aerosols. Efforts to set a scientifically defensible standard have been hampered by the failure to identify the specific active agents, chemical and/or physical, to which the health effects can be ascribed. This proposal describes novel methods for characterizing the submicron aerosol morphologically and chemically. The principal objectives are to (1) establish the prevalence and physical properties of the two morphological ranges (ultrafine agglomerates (dp < 0.1 æm) and accumulation mode (0.1 to 1.0 æm) micro-droplets), (2) determine certain characteristics of the ranges as they relate to active agent hypotheses for health effects including fractal properties for the ultrafine particles and aerosol oxidant concentrations in the accumulation mode, (3) integrate morphological concepts into conventional approaches to aerosol characterization to produce a new synthesis for characterizing ambient submicron aerosols, and (4) apply the results to the dynamics of the atmospheric aerosol.
Atmospheric aerosols will be sampled using a low pressure impactor and/or thermal precipitator. Morphological studies will be made of the deposited particles using electron microscopy. Individual particles will be analyzed using electron microscopy coupled with chemical analytical techniques. These measurements will provide information on particle-to-particle variation in composition and the internal structure of accumulation mode particles. Ion concentrations in the accumulation mode may be detectable only qualitatively. Also of interest are the origins of aerosol oxidants in the aqueous component of the accumulation mode, including peroxides from the gas phase and the products of aqueous reactions involving transition metal ions. A feasibility study of measurement methods for aerosol oxidants will be included as part of this task; we do not propose to develop a technique for the purpose.
New morphological data on the ultrafine and accumulation ranges will be combined with existing theoretical representations of the atmospheric aerosol to arrive at a new synthesis. The relevant parameters are ultrafine particle fractal structure and primary particle diameter, and information on the aqueous component in accumulation mode particles.
It has been conjectured that the biological effects of ultrafine particles result from the accumulation of nanoparticles in the interstitium of the alveolar cells. The nanoparticles in the alveolar region presumably come from the transport of ultrafine agglomerates from the atmosphere into the lower lung. The process depends on fractal dimension and primary particle size of the agglomerates, information that will be provided by the proposed studies.
Several hypotheses concerning the health effects of ambient aerosols relate to the oxidizing behavior of the particles. Methods for measuring aerosol phase oxidants, identified in the feasibility study, would permit improved epidemiological studies to test specific mechanisms.
The results will help guide future studies of animal and human exposures to aerosols. Detailed information on the morphology of particles in the ambient aerosol obtained in this study should be incorporated into future studies of aerosol health effects.