Understanding factors affecting partitioning of oxygenated organics in natural and polluted environments using SV-TAG

Wednesday, 17 December 2014
Gabriel A Isaacman1, Lindsay Yee1, Nathan M Kreisberg2, Joshua Moss1, Weiwei Hu3, Pedro Campuzano Jost3, Douglas A Day4, Brett B Palm3, Jose L Jimenez3, Suzane S de Sá5, Scot T Martin6, M. Lizabeth Alexander7, Thien Khoi V Nguyen8, Annmarie G. Carlton9, Juarez Viegas10, Stephen R. Springston11, Antonio O Manzi12, Rodrigo Augusto Ferreira de Souza13, Maria B Oliveira13, Paulo Artaxo14, Joel Ferreira De Brito14, Eric S Edgerton15, Karsten Baumann16, Susanne V Hering2 and Allen H Goldstein1, (1)University of California Berkeley, Berkeley, CA, United States, (2)Aerosol Dynamics Inc., Berkeley, CA, United States, (3)University of Colorado at Boulder, Boulder, CO, United States, (4)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (5)Harvard University, School of Engineering and Applied Sciences, Cambridge, MA, United States, (6)Harvard University, Cambridge, MA, United States, (7)Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA, United States, (8)Rutgers University New Brunswick, Bronx, NY, United States, (9)NOAA Earth System Research Lab, Boulder, CO, United States, (10)Instituto Nacional de Pesquisas da Amazonia, Manaus, AM, Brazil, (11)Brookhaven National Laboratory, Upton, NY, United States, (12)Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil, (13)Universidade do Estado do Amazonas, Manaus, AM, Brazil, (14)USP University of Sao Paulo, São Paulo, Brazil, (15)Atmospheric Research & Analysis, Inc., Cary, NC, United States, (16)Atmospheric Research & Anal., Morrisville, NC, United States
Most known organic tracers and compounds present in atmospheric aerosols are sufficiently volatile to partition between the gas and particle phases, affecting oxidation timescales and pathways. However, few direct measurements are available of ambient gas-to-particle partitioning of individual compounds, and the effect of anthropogenic emissions on the partitioning of biogenic aerosol components is not well-studied. Using hourly measurements of gas- and particle-phase organics in the atmosphere we identify here those factors that are most significant in modeling partitioning. Concentrations and partitioning of oxidation products of biogenic emissions were measured in two locations: the Southeastern U.S. (SOAS 2013) and Amazonia, Brazil (GoAmazon 2014). At both sites, high levels of biogenic emissions interact with plumes from nearby cities, creating an ideal environment to study the influence of anthropogenic emissions on environmental factors expected to affect partitioning (i.e. acidity, liquid water content). A Semi-Volatile Thermal desorption Aerosol Gas chromatograph (SV-TAG) was modified to include simultaneous collection of particle-phase and total gas- and particle-phase compounds, as well as derivatization of hydroxyl groups prior to GC analysis to enable measurement of oxygenates. Co-located instruments measuring trace gases and particle properties provide additional insight into oxidation chemistry and anthropogenic influence. Traditional equilibrium partitioning is found to often underpredict, and almost never overpredict, the particle-phase fraction of a compound with a highly variable deviation between measured and modeled partitioning. Furthermore, the ability of traditional models to describe measured partitioning is strongly compound dependent: some compounds are reasonably well-described, while others are consistently far more in the particle-phase than predicted. Chemical differences are used to explore the role of particle-phase formation of lower-volatility thermally labile or reactive species (i.e. oligomers) that may be observed as monomers or precursors. Temporal and chemical variability provide insight into the mechanisms driving partitioning and better constrain the transition between gas-phase species and organic aerosol.