Hypotheses to be Tested (Summary)

The Pittsburgh Supersite Program has been designed to test a wide range of complementary hypotheses. The first group of hypotheses fall solely under the purview of the EPA Supersite program and can be tested with atmospheric measurements related to meteorology and air quality, specifically gas-phase pollutant concentrations and the size and composition of PM. A wide range of data will be collected under funding primarily from DOE that will supplement the ambient measurements and support other aspects of the measurement program such as indoor air quality assessment. Finally, health effects data will be collected under funding from other agencies, and combined with the ambient and indoor measurements will provide a rich data set for the planned epidemiological study. A brief summary of the corresponding topics is presented below. For a detailed overview of the hypotheses, select this link:

Hypotheses and Their Testing

1. Ambient aerosol characterization: The Supersite measurements will attempt to resolve the lack of mass balance often observed in the PM samples in the Eastern US and will quantify the total number and surface area concentrations continuously.

2. Measurement methods: A number of new PM measurement technologies (single particle measurements, semi-continuous measurements of elements, nitrate, sulfate, and carbon) will be developed further and will be evaluated against the traditional filter techniques. Artifacts introduced during the nitrate and semivolatile organics sampling in the area will be investigated.

3. Atmospheric processes: The sources of particle number (emissions versus nucleation), the contributions of biogenic sources (primary and secondary), the role of fogs and clouds in the sulfate production, the response of the PM to sulfate changes and the role of ammonia, the relative contributions of primary and secondary organic PM sources, and the impact of local versus regional sources will all be investigated based on a set of six hypotheses.

4. Source-Receptor Relationships: One of the main hypotheses of the proposed program is that the combination of state-of-the-art-techniques like the single particle measurements, organic PM tracers, continuous elemental concentration measurements, etc., together with meteorological information (e.g., air trajectories) and source-receptor models will allow an unprecedented resolution of source contributions to local air quality by receptor modeling techniques.

5. Aerosol Properties: The interactions of particles with water (growth, deliquescence, crystallization, existence of metastable phases, and cloud droplet formation) and their optical properties will be quantified as a function of their chemical composition.

6. Health Effects: The combination of the Supersite data set with the epidemiological study will allow the testing of practically all of the hypotheses that have been proposed to explain the PM effects on mortality and morbidity.

7. Indoor Exposure: The combination of the Supersite measurements with the indoor monitoring study will examine the relationships between ambient and indoor PM levels as a function of particle size, chemical composition, season, housing stock characteristics.