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ACS Earth Space Chem

Title:		Bidirectional Ecosystem-Atmosphere Fluxes of Volatile Organic Compounds Across the Mass Spectrum: How Many Matter?
Author(s):		Millet DB; Alwe HD; Chen X; Deventer MJ; Griffis TJ; Holzinger R; Bertman SB; Rickly PS; Stevens PS; Leonardis T; Locoge N; Dusanter S; Tyndall GS; Alvarez SL; Erickson MH; Flynn JH;
Address:		"University of Minnesota, Saint Paul, Minnesota 55108, United States. Utrecht University, Utrecht 3584 CC, The Netherlands. Western Michigan University, Kalamazoo, Michigan 49008, United States. Indiana University, Bloomington, Indiana 47405, United States. IMT Lille Douai, Univ. Lille, SAGE - Departement Sciences de l'Atmosphere et Genie de l'Environnement, 59000 Lille, France. National Center for Atmospheric Research, Boulder, Colorado 80305, United States. University of Houston, Houston, Texas 77004, United States"
Journal Title:		ACS Earth Space Chem
Year:		2018
Volume:		20180614
Issue:		8
Page Number:		764 - 777
DOI:		10.1021/acsearthspacechem.8b00061
ISSN/ISBN:		2472-3452 (Print) 2472-3452 (Electronic)
Abstract:		"Terrestrial ecosystems are simultaneously the largest source and a major sink of volatile organic compounds (VOCs) to the global atmosphere, and these two-way fluxes are an important source of uncertainty in current models. Here, we apply high-resolution mass spectrometry (proton transfer reaction-quadrupole interface time-of-flight; PTR-QiTOF) to measure ecosystem-atmosphere VOC fluxes across the entire detected mass range (m/z 0-335) over a mixed temperate forest and use the results to test how well a state-of-science chemical transport model (GEOS-Chem CTM) is able to represent the observed reactive carbon exchange. We show that ambient humidity fluctuations can give rise to spurious VOC fluxes with PTR-based techniques and present a method to screen for such effects. After doing so, 377 of the 636 detected ions exhibited detectable gross fluxes during the study, implying a large number of species with active ecosystem-atmosphere exchange. We introduce the reactivity flux as a measure of how Earth-atmosphere fluxes influence ambient OH reactivity and show that the upward total VOC ( summation operatorVOC) carbon and reactivity fluxes are carried by a far smaller number of species than the downward fluxes. The model underpredicts the summation operatorVOC carbon and reactivity fluxes by 40-60% on average. However, the observed net fluxes are dominated (90% on a carbon basis, 95% on a reactivity basis) by known VOCs explicitly included in the CTM. As a result, the largest CTM uncertainties in simulating VOC carbon and reactivity exchange for this environment are associated with known rather than unrepresented species. This conclusion pertains to the set of species detectable by PTR-TOF techniques, which likely represents the majority in terms of carbon mass and OH reactivity, but not necessarily in terms of aerosol formation potential. In the case of oxygenated VOCs, the model severely underpredicts the gross fluxes and the net exchange. Here, unrepresented VOCs play a larger role, accounting for ~30% of the carbon flux and ~50% of the reactivity flux. The resulting CTM biases, however, are still smaller than those that arise from uncertainties for known and represented compounds"
Keywords:		chemical transport model deposition eddy covariance emissions flux reactivity volatile organic compounds;
Notes:		"PubMed-not-MEDLINEMillet, Dylan B Alwe, Hariprasad D Chen, Xin Deventer, Malte Julian Griffis, Timothy J Holzinger, Rupert Bertman, Steven B Rickly, Pamela S Stevens, Philip S Leonardis, Thierry Locoge, Nadine Dusanter, Sebastien Tyndall, Geoffrey S Alvarez, Sergio L Erickson, Matthew H Flynn, James H eng NNX14AP89G/NASA/NASA/ 2018/08/16 ACS Earth Space Chem. 2018 Aug 16; 2(8):764-777. doi: 10.1021/acsearthspacechem.8b00061. Epub 2018 Jun 14"