Cooperative Institute for Research in Environmental Sciences

Potential Aerosol Mass (PAM) flow-through reactor measurements of SOA formation from BEACHON-RoMBAS

Brett B. Palm (1,2), Amber M. Ortega (1,3), Pedro Campuzano-Jost (1,2), Douglas A. Day (1,2), Thomas Karl (4), Lisa Kaser (5), Werner Jud (5), Armin Hansel (5), Juliane L. Fry (1,6), Steven S. Brown (7), Kyle Zarzana (1,2), William Dube (1,7), Nick Wagner (1,7), Danielle Draper (6), William H. Brune (8), and Jose L. Jimenez (1,2)

(1) CIRES, (2) Department of Chemistry and Biochemistry, University of Colorado, (3) Department of Atmospheric and Oceanic Science, University of Colorado, (4) NCAR, (5) Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria, (6) Department of Chemistry and Environmental Studies, Reed College, (7) Chemical Sciences Division, NOAA, (8) Department of Meteorology, Pennsylvania State University

A Potential Aerosol Mass (PAM) photooxidation reactor (Kang et al., ACP 2007, 2010) was used in conjunction with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (DeCarlo et al. Anal. Chem. 2006; HR-ToF-AMS) to characterize biogenic secondary organic aerosol formation during the July-August 2011 BEACHON-RoMBAS field campaign at the U.S. Forest Service Manitou Forest Observatory, Colorado. The PAM reactor uses mercury lamps to create OH concentrations up to 10,000 times ambient levels. High oxidant concentrations accelerate the photooxidation of volatile organic compounds and inorganic gases, which then partition into the aerosol phase. PAM photochemical processing can represent up to approximately 20 days of equivalent atmospheric aging in the span of 4 minutes of residence time in the reactor, and PAM-processed aerosols have shown similar aging signatures as well as sulfate and SOA yields when compared to aging ambient aerosols (Kang et al., ACP 2010; Lambe et al., ACP 2011). The reactor was also injected with O3 or N2O5 in the absence of lights to investigate oxidation by O3 or NO3, oxidants that are expected to have increased importance at locations dominated by biogenic emissions. Presented here is the analysis of PAM processed aerosols using an HR-ToF-AMS, a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS), and an NO3/N2O5 instrument. Preliminary results show that PAM photooxidation enhances SOA at intermediate OH exposure (1-10 equivalent days) but results in net loss of OA at very long OH exposure (10-20 equivalent days). PAM oxidation also results in a Van Krevelen diagram (H/C vs. O/C) slope similar to ambient oxidation. Oxidation with NO3 is shown to result in significant SOA production, and both OH and N2O5/NO3 oxidation cause production of NH4NO3 at low nighttime temperatures.