Turbulent Flux Measurements and Transfer Velocity Estimates of Nucleation-sized Particles

NICHOLAS MESKHIDZE, Ajmal Rasheeda Satheesh, Sabin Kasparoglu, Mohammad Maksimul Islam, Bethany Sutherland, Markus Petters, NC State University

     Abstract Number: 285
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
The eddy-covariance flux measurements of >3 and >10 nm particles were conducted at the DOE ARM SGP site in Oklahoma. The main objective of the field campaigns was to examine the feasibility of measuring particle fluxes to distinguish between ground-level and residual-layer New Particle Formation (NPF) events. Equipment deployed included a 10-m telescopic tower, multiple condensation particle counters, a sonic anemometer, a scanning mobility particle sizer (SMPS), a Printed Optical Particle Spectrometer, and a humidified tandem differential mobility analyzer. Our measurements were supplemented by the ancillary data obtained from the ARM facilities, such as radiosondes, Aerosol Observing System SMPS and nano-SMPS, vertically pointed Doppler Lidar, and the University of Wisconsin High Spectral Resolution Lidar.

Here we show that when 3-10 nm-sized particles appear at the ground level, the derived flux signs are representative of the directional transport of particles: the negative fluxes indicate downward transport, i.e., the NPF happens aloft, while the positive fluxes denote upward transport, i.e., the NPF occurs near the surface. Hygroscopic growth factor measurements for 15, 20, 30, 40, and 50 nm-sized particles indicated growth factors much smaller than those of ammonium sulfate, suggesting that organic compounds dominated the sub-50 nm sized particle chemical composition. Flux measurements also allowed us to examine 3-10 nm-sized particle dry deposition velocity. Although both the positive and the negative values of the deposition velocity inferred in this study are comparable to the values reported in the literature, we argue that the methodology for calculation of the deposition velocity (assuming zero particle concentration very near the surface, at the top of the diffusion sublayer) is inadequate for the estimation of sub-10 nm particle deposition velocities in most environments.

A similar eddy-covariance flux measurement setup will be deployed during the TRACER campaign and we anticipate showing the first results.