A036-0016
Quantifying speciated aerosol removal in the remote troposphere: Constraints on physical and chemical removal of organic aerosol (OA) provided by the ATom mission.
Tuesday, 8 December 2020
Poster
Pedro Campuzano Jost1,2, Benjamin A Nault3, Jason Clay Schroder4, Duseong Jo5, Alma Hodzic6, Doug A Day3, Jose L Jimenez3, Joseph M Katich7, Joshua Peter Schwarz8, Gregory P Schill9, Karl D Froyd9, Louisa K Emmons6, Simone Tilmes10, Nicola J Blake11, Donald Ray Blake11, Bruce C Daube12, Roisin Commane13, Steven C Wofsy14, Huisheng Bian15, Peter Richard Colarco16, Mian Chin17, Pengfei Yu18, Eric A Ray19, Karen Hepler Rosenlof20, Paul A. Newman21, Jack Kodros22, Anna Lily Hodshire23 and Jeffrey R Pierce24, (1)University of Colorado at Boulder, Department of Chemistry, Boulder, CO, United States, (2)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (3)University of Colorado at Boulder, Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Chemistry, Boulder, CO, United States, (4)Colorado Department of Public Health and Environment, Denver, CO, United States, (5)University of Colorado at Boulder, Chemistry/CIRES, Boulder, CO, United States, (6)National Center for Atmospheric Research, Boulder, CO, United States, (7)University of Colorado Cooperative Institute for Research in Environmental Sciences (CIRES) at the NOAA Chemical Sciences Laboratory (CSL), Boulder, CO, United States, (8)NOAA Chemical Sciences Laboratory (CSL), Boulder, CO, United States, (9)NOAA/CIRES, Boulder, CO, United States, (10)National Center for Atmospheric Research, Atmospheric Chemistry, Observations, and Modeling Laboratory, Boulder, CO, United States, (11)University of California Irvine, Irvine, CA, United States, (12)Harvard University, John A. Paulson School of Engineering and Applied Sciences, Cambridge, MA, United States, (13)Columbia University in the City of New York, New York, NY, United States, (14)Harvard Univ, Cambridge, MA, United States, (15)NASA Goddard Space Flight Ctr, Greenbelt, MD, United States, (16)NASA GSFC, Greenbelt, MD, United States, (17)NASA Goddard SFC, Greenbelt, MD, United States, (18)CIRES, Boulder, CO, United States, (19)NOAA/CIRES, Boulder, United States, (20)NOAA Earth System Research Laboratory, Chemical Sciences Division, Boulder, CO, United States, (21)NASA GSFC, Code 610, Greenbelt, MD, United States, (22)Colorado State University, Atmospheric Science, Fort Collins, CO, United States, (23)Colorado State University, Chemistry, Fort Collins, CO, United States, (24)Colorado State University, Department of Atmospheric Science, Fort Collins, CO, United States
Abstract:
Organic aerosol (OA) is one of the major contributors to the PM2.5 burden both in the continental Northern Hemisphere and globally. Understanding its sources and aging is central to air pollution and climate mitigation. In the course of the recent NASA Atmospheric Tomography (ATom) aircraft missions, we have acquired four unique global datasets of submicron aerosol composition over the remote Atlantic and Pacific Oceans. Based on this dataset, in the remote free troposphere (FT) OA and sulfate are the main fine aerosol components (about 0.3 µg sm-3 in total, fairly constant outside of continental outflow). While the general compositional trends are mostly reproduced in updated chemical transport models (CTMs), a detailed analysis shows that models fail to account for:
- The predominance of sulfate over OA In the cleanest/most remote parts of the global FT.
- The observed compositional gradients in convection, suggesting – as shown already for BC and seasalt – that model skill in the FT might be partially due to a compensating error of insufficient removal.
- The much higher average carbon oxidation state of OA in the remote FT than in continental air masses (OSc up to +1 compared to -1 over the continents), suggesting a fairly hygroscopic OA.
This suggests that CTMs underestimate removal of OA, likely underestimate sources and certainly underestimate the chemical aging of OA.
Using several different photochemical clocks and confirming back trajectories to infer the age of the air masses sampled during ATom, we estimate that the chemical (total) lifetime of OA in the remote UT is of the order of 10-13 (4) days. In contrast, for chemically inert black carbon, the estimated removal timescale using the same method is about a week, in general agreement with previous estimates of physical removal. The significantly shorter OA lifetime suggests an additional, chemical removal mechanism. This provides a key constraint for modeling of OA in the FT, based solely on measurements. Both heterogeneous oxidation by OH and aerosol photolysis are possible pathways for OA removal that have been suggested previously. Sensitivity studies in two CTMs, CESM2 AND GEOS-Chem with updated chemistry and aerosol sources are used to constrain the relative importance of each pathway for OA removal during ATom
