1. First Define the Information Needed, Then Select a Course of Action John S. Irwin, NOAA EPA, OAQPS Air Quality Modeling Group RTP, NC 27711

2. Support Roles Office of Air Quality Planning and Standards - provides expertise for assessment of possible longer-term (chronic) health risks. Chemical Emergency Preparedness and Prevention Office - provides direct support in assessing risks for emergency situations (operational and planning).

3. Chronic Health Effects Three pathways: air, food, dermal. Activity patterns: micro-environments [water contamination (cooking, cleaning, washing)]. Long-term exposures: time integral

4. Information Needs Defining media (pathways) Defining emissions (species, amounts, physical size, physical characteristics) Defining possible risks

5. Leading Questions Do we need to know where the emissions are going? If so, how accurately? Do we need to know actual concentration levels? If so, how accurately?

6. Analysis Issues How close are people: emission characterization demands Land use (rural, urban, terrain, large lakes): dilution effects, wind fields, local circulation's Meteorological situation: predictability Emission characterization

7. Uncertainties Location of plume: one-fourth of plume’s width (factor of 2). Plume’s dispersion: factor of 2. Emission characterization: amount released, mass flow rate, temperature, initial volume, etc. (factor of 2).

8. Coping with Uncertainty Chronic effects involve long-term averages. This will mitigate stochastic effects. Do we know what is currently being emitted at the NY Trade Center site? If so, by what means? Acute effects involve short-term values at specific locations. At what level of uncertainty do simulation results become worthless?

9. Summary Focus on the information needs –What needs to be known –When does it need to be known? –How accurately? Look for the hidden Gotcha –Change in meteorological conditions –Local circulation's –The not so obvious emissions Modeling versus Monitoring