Size-dependent aerosol deposition velocities during BEARPEX'07

Abstract

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≤D p ≤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 (V 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 V d increases with friction velocity and particle diameter.

Eddy covariance measurements with high-resolution time-of-flight aerosol mass spectrometry: a new approach to chemically resolved aerosol fluxes

“…We observed deposition of NR-PM 1 during the BEARPEX-2007 campaign, consistent with particle number fluxes (Vong et al, 2010). Ammonium deposited to the forest surface.…”

“…In addition, the fluxes are derived from the aerosol mass within a certain size-range, which may not be a conserved parameter where the aerosol size changes beyond the upper or lower size cut-off during vertical transport. By integrating over the total accumulation mode mass of the chemical components, the HR-AMS is relatively insensitive to changes in size distribution within the instrument's submicron range, and we can generally consider the HR-AMS flux measurement to be insensitive to artifacts due to the small changes in submicron particle size caused by evaporation/condensational growth, which have been found to affect the measurement of size-segregated particle number fluxes within individual accumulation mode size bins or fluxes of total particle number above a specified cutoff (e.g., Nemitz et al, 2004aNemitz et al, , 2009aVong et al, 2010). Under some conditions, however, vertical gradients in particle growth in or out of the AMS-observable size range due to water uptake or changes in gas/aerosol partitioning with condensable chemical species could, however, cause an artifact.…”

“…While frequently applied to CO 2 and other gas phase species, the application of the eddy covariance approach to aerosols has been limited by the stringent instrumental requirements: measurements must not only be portable and free of interference, but they must also be fast and sensitive enough to capture fluctuations on the time scale of flux-carrying turbulent eddies (≥5 Hz). Fluxes of total or size-resolved aerosol number (without chemical information) have been performed for some time (e.g., Katen et al, 1985;Sievering, 1987;Buzorius et al, 1998;Dorsey et al, 2002;Mårtensson et al, 2006;Vong et al, 2010). However, total and chemically-resolved particle mass fluxes have lagged behind because most instruments measuring mass or aerosol chemical composition are far from meeting the rigorous requirements for EC, and most chemically-resolved aerosol flux measurements have been indirect with slower time resolution approaches (e.g., Nemitz et al, 2004b;Trebs et al, 2006;Myles et al, 2007;Thomas et al, 2009;Wolff et al, 2010).…”

“…High nitrogen fertilization levels, however, can reduce forest health and cause plant death and loss of diversity (Matson et al, 2002;Magill et al, 2004;Stevens et al, 2004). Further, while particle fluxes are known to be size dependent (Vong et al, 2010), they are also expected to be chemically dependent (Erisman et al, 1997;. Models typically include size-dependent particle fluxes, but do not allow for upward fluxes of particles from ecosystem surfaces, let alone chemically-resolved deposition fluxes.…”

N<sub>2</sub> fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise)

“…Each sample was subjected to two contact times: the first contact was at 1 min, and the second contact was at 24 h. NO x was analysed using a 1 m long liquid waveguide capillary cell (LWCC) made of quartz capillary tubing, following the protocol described in Louis et al (2015). An extrapolated NO x release from dry deposition was estimated on the basis of a deposition velocity of submicron particles (0.4 m s −1 ; Vong et al, 2010).…”