Size-dependent aerosol deposition velocities during BEARPEX'07

Abstract

Aerosol concentrations and 3-D winds were measured from 9 to 25 September 2007, above a pine forest in California. The measurements were combined using the eddy covariance (EC) technique to determine aerosol eddy fluxes as a function of particle diameter within the accumulation mode size range (0.25 μm&le;<i>D</i>_p&le;1 μm here). Measured heat and water vapor fluxes were utilized to correct the aerosol eddy fluxes for aerosol hygroscopic growth. The hygroscopic growth correction was necessary despite the low RH and relatively hygrophobic nature of the particles. Uncertainties associated with particle counting also were evaluated from the data. Aerosol deposition velocities (<i>V</i>_d = EC turbulent flux/mean particle concentration) during daytime were shown to vary from −0.2 to −1.0 cm s⁻¹; the magnitude of particle <i>V</i>_d increases with friction velocity and particle diameter.