Dust resuspension under weak wind conditions: direct observations and model

Abstract

Abstract. The results of direct observations of fine mineral dust aerosol (0.15-15 µm) were carried out on extensive sand areas in desertificated lands of Kalmykia in 2007Kalmykia in , 2009Kalmykia in , and 2010 under conditions of weak wind and strong heating of the surface, almost in the absence of saltation processes. These results show that the fine mineral dust aerosol (0.15-0.5 µm) in the region under consideration contributes considerably to the total aerosol content of the atmospheric surface layer. Data on the mass concentrations of fine aerosol are treated on the basis of physical model estimates obtained for fluid dynamic parameters in the viscous thermal boundary layer near the ground surface. Deviations of these mass concentrations from their background values are related to a temperature drop in the thermal layer at the surface and from the values of friction velocity. For small and moderate values of friction velocity, these mass concentrations increase proportionally to a temperature drop with an exponent of about 0.5, and, for high friction velocities, this exponent becomes negative (∼−0.5), which implies a decrease in these concentrations with an increase in a temperature drop.

Seasonality in the Δ<sup>33</sup>S measured in urban aerosols highlights an additional oxidation pathway for atmospheric SO<sub>2</sub>

“…It is worth mentioning that weak wind conditions can also be responsible for a high contribution of fine (0.15-15µm) mineral dust fraction in the total aerosol content (Golitsyn et al, 1997;Golitsyn et al, 2003;Chkhetiani et al, 2012), being also observed in Beijing during the winter haze episodes (Yang et al, 2017;Yang et al, 2018) where negative Δ 33 S-values primarily occur (Han et al, 2017). Although the contribution of sulfates from terrigeneous sources has been estimated to a maximal value of 3.84 ± 4.40 to 5.62 ± 6.52% deduced from Ca² + concentration (Han et al, 2017).…”

Further development of a parameterization for convective turbulent dust emission and evaluation based on field observations

“…Recently, effort has been made to investigate the process of Convective Turbulent Dust Emission (CTDE), the most important form of aerodynamic dust entrainment [ Klose and Shao , ]. Field experiments have been carried out to investigate CTDE among other processes [e.g., Heintzenberg , ; Chkhetiani et al , ]. Ansmann et al [] analyzed the vertical profiles of convective dust plumes by use of lidar measurements of the Saharan Mineral Dust Experiment (SAMUM) in Morocco and suggested that convective processes play an important role in dust production, particularly at low mean wind speeds (< 7 ms −1 ).…”

Convective turbulent dust emission (CTDE) observed over Horqin Sandy Land area and validation of a CTDE scheme

“…While strong dust events are important to episodic increases in atmospheric dust concentration, CTDE is arguably more important in maintaining the background dust concentration and the continuous dust supply to the ocean to sustain the ocean biomass productivity [ Klose and Shao , ]. Thus, CTDE contributes to global dust variability mainly on seasonal, annual, or longer time scales [ Chkhetiani et al ., ]. The importance of CTDE is however yet to be fully quantified.…”

“…Dust emission without saltation has been observed in field and wind tunnel experiments [ Gillette and Sinclair , ; Shao et al ., ; Gillette et al ., , ; Loosmore and Hunt , ; Golitsyn et al ., ; Chkhetiani et al ., ]. Most of the field experiments on CTDE are carried out in desert regions [e.g., Gillette and Sinclair , ; Gillette et al ., ].…”

“…Chkhetiani et al . [] found that under weak wind conditions ( u * < 0.30 m s −1 ), the deviations of mass concentration of fine dusts (0.15–0.50 µm) from their background values, increased proportionally to the temperature drop between the surface and the air at 0.2 m with an exponent of about 0.5, based on the observational data from an extensive sand area in Kalmykia. However, there are rare long‐term field observations of CTDE to study its seasonal evolution and its characteristics over different soil conditions.…”