In this study, eddy covariance measurements of aerosol number fluxes from the Canopy Horizontal Array Turbulence Study (CHATS) in Dixon, CA are presented and compared to relaxed eddy accumulation simulations. The validity of the similarity assumption of different scalars such as aerosol number concentration, temperature and water vapor density will be evaluated and discussed.
From the high-resolution time series of these scalars, b factors are calculated using various definitions of updraft and downdraft conditions, i.e. different wind deadbands. Depending on the selected deadband, the sampling process is concentrated towards strong updrafts and downdrafts, which increases the scalar concentration difference between the updraft and downdraft reservoirs. This is compensated by a decrease in the corresponding b factor. While functional relationships of this dependence have been suggested for various scalars including temperature, CO2, and H2O, we are not aware of previous investigations of this relationship with regard to ultrafine aerosol number concentrations.
This study contributes to a better understanding of the turbulent transport of aerosol particles in the boundary layer, and selecting appropriate proxy scalars in future relaxed eddy accumulation applications for aerosol flux measurements.