1. SECONDARY ORGANIC AEROSOLS WORKSHOP OVERVIEW John G. Watson Desert Research Institute, Reno, NV February 5, 2002

2. Primary and Secondary Aerosol Primary aerosol: Directly emitted from sources as particles Secondary aerosol: Formed in the atmosphere from directly emitted gases Secondary inorganic aerosol: Sulfuric acid, ammonium bisulfate, ammonium sulfate, ammonium nitrate Secondary organic aerosol: Many oxygenated and nitrated compounds

3. What We Know Organic carbon (OC) is a substantial fraction (20% to 70%) of average PM 2.5 at urban and non-urban locations OC derives from many sources, both natural and manmade, of ancient (fossil fuels >1M years old) and recent (<100 year) origin OC derives from directly emitted particles (primary organic aerosol, POA) and gaseous precursors that change into particles (secondary organic aerosol, SOA) Reductions in SOA precursor emissions may not result in reductions of SOA, and may result in SOA, ozone, and secondary inorganic PM 2.5 increases under some circumstances

4. What We Need to Know What fraction of ambient OC is SOA? How does it form in the atmosphere? Where do the precursors come from? How is it measured? How does SOA affect health, visibility, and climate? How will SOA concentrations to changes in precursor emissions?

5. Workshop Goals Create a snapshot of current knowledge. Specify near, medium, and long-term research needed to advance knowledge. Create a research strategy to guide and promote the specified research.

6. Workshop Process Supply initial answers to specific questions about SOA guided by a small group of experts Identify knowledge gaps and ways to fill them Solicit additional information from the broader research community