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MAE Publications and Papers

Sibley School of Mechanical and Aerospace Engineering

New article: Ultrafine Particle Number Fluxes over and in a Deciduous Forest

Article: Pryor, SC; Barthelmie, RJ; Larsen, SE; Sorensen, LL; “Ultrafine Particle Number Fluxes over and in a Deciduous Forest”, Journal of Geophysical Research-Atmospheres, 122 (1): 405-422


Abstract:  Ultrafine particles (UFP, particles with diameters (D-p) < 100 nm) play a key role in climate forcing; thus, there is interest in improved understanding of atmosphere-surface exchange of these particles.

Long-term flux measurements from a deciduous forest in the Midwestern USA (taken during December 2012 to May 2014) show that although a substantial fraction of the data period indicates upward fluxes of UFP, on average, the forest is a net sink for UFP during both leaf-active and leaf-off periods. The overall mean above-canopy UFP number flux computed from this large data set is -4.90 x 10(6) m(-2) s(-1) which re-emphasizes the importance of these ecosystems to UFP removal from the atmosphere. Although there remain major challenges to accurate estimation of the UFP number flux and in drawing inferences regarding the actual surface exchange from measurements taken above the canopy, the above the canopy mean flux is shown to be downward throughout the day (except at 23.00) with largest-magnitude fluxes during the middle of the day. On average, nearly three quarters of the total UFP capture by this ecosystem occurs at the canopy. This fraction increases to 78% during the leaf-active period, but the over-story remains dominant over the subcanopy even during the leaf-off period.

Funding Acknowledgement:  NSF [1517365, 1102309]; Office of Science, U.S. Department of Energy; AmeriFlux Management Project, Lawrence Berkeley National Laboratory

Funding Text:  The research presented herein was supported by grants to S.C.P. from NSF (1517365 and 1102309) and high-performance computing infrastructure provided by the Lilly Endowment, Inc. to the Indiana University Pervasive Technology Institute and the Indiana METACyt Initiative. The AmeriFlux data used herein (available at: were collected under funding from the Office of Science, U.S. Department of Energy, and from the AmeriFlux Management Project, Lawrence Berkeley National Laboratory. The NWS snow data are available for download from the NOAA National Centers for Environmental Information (access at All other flux data presented herein are available for download from Discussions with Ebba Delwik and Anna-Maria Sempreviva of DTU-Wind Energy are appreciated, as is technical assistance from Steve Scott and Karen Hornsby of Indiana University.

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