1. Organic Carbon during AMAZE-08: Preliminary model analysis AMAZE Science Team Meeting, Boulder July 24, 2008 Colette L. Heald (heald@atmos.colostate.edu) With observations from: Qi Chen & Scot Martin (Harvard University), Delphine Farmer & Jose Jimenez (CU Boulder), Thomas Karl & Alex Guenther (NCAR), Paulo Artaxo (University Sao Paulo) And discussion with: Andi Andreae, Tony Prenni

2. GEOS-Chem AEROSOL SIMULATION 2ºx2.5º global simulation with climatological emissions Site isolated from anthropogenic sources, monthly mean aerosol concentrations dominated by OC and dust…Unfortunately with consistent cloud cover, no satellite AOD available to validate distributions FEB: Surface Concentrations

3. ORGANIC CARBON: GEOS-Chem Simulated surface OC at site ~0.5-1 µg/m 3, dominated by POA and monoterpene SOA. NOTE: there is no PBAP source here.

4. COMPARISON WITH AMS OBSERVATIONS Early Feb: observe significantly more organic aerosol than simulated (rain ends this period) Field site in Amazonia, Feb-Mar Observations = 1-4 µg/m 3 Point #1: For majority of campaign GEOS-Chem simulates similar amount of OC (~1 µg/m 3 ) Point #2: Observed concentrations are relatively low (somewhat explains #1) Point #3: There’s an interesting discrepancy early in the campaign….source?? Point #4: Consistent airflow throughout campaign simplifies analysis – no change in source influence Consistent air flow throughout campaign:

5. ARE FIRES A LIKELY SOURCE? Feb 1-9 Feb 21-29 MODIS fire counts: http://maps.geog.umd.edu/firms/maps.asp Fires in the region during early Feb. These are not reflected in model emission inventories. Elevated OC is coincident with elevated acetonitrile and potassium. MODIS detects actives fires in the immediate region.

6. …WHAT ABOUT FIRES IN AFRICA? Surface OC concentrations simulated by GEOS-Chem (with climatological fire source) OC from African fires could be transported…or potassium from African dust? Fires from early Feb transported across Atlantic?

7. CONCLUSIONS…(SO FAR) No significant “unexplained” sub-micron OC observed at field site Elevated OC in early Feb likely fire related  hope that a GEOS-Chem simulation with 2008 fire emissions can help determine if South American or African fire source is likely  Note that the AMS m/z 60 / Org ratio does not indicate a strong fire influence Interestingly, This leaves little room for underestimated BSOA formation or sub-micron PBAP From Andi Andreae (unpublished data) How does this mesh with our thinking on PBAP?