Field Experimental Research On Dust Emission Characteristics Of The Farmland Surface

The semi-arid bare farmland of northern China is important sources of dust.At present,there are few field experiment data on dust emission characteristics,at the same time,the attention to the dynamic change of dust concentration or flux in the process of aerodynamic entrainment is far from enough.In this work,a new wind erosion measurement device is introduced,which is based on the dust emission mechanisms and field wind-tunnels.Mainly has carried out the following work:First,we measured the distribution of wind velocity and shear stress at varying RPM with Pitot tube and Irwin sensors,and the characteristics of near-surface air flow were quantitatively described from the perspective of shear stress;Second,using the new device,we carried out field experiments on the dust emission characteristics for five kinds of farmland surface,and investigated the threshold shear velocity and emission flux on dust emitted by aerodynamic entrainment,simultaneously,the reliability of measurement data was verified by comparing with wind tunnel experiments and field observations.Finally,we analyzed the influence of artificial disturbance on the characteristics of dust emission.Results indicate that: the aerodynamic entrainment has a dynamic process of twophase emission response: transient high-concentration peak phase and long-term low-concentration residual phase: dust concentration exhibit an initial relatively high “peak” followed by an ‘‘asymptotic'' approach to some lower value.Artificial disturbance has a significant influence on dust emission flux and threshold friction velocity: which will change the structure of the soil surface,destroy the bond strength among soil particles those are existed in aggregates,generate more free dust,reduce the threshold friction velocity on dust emitted by aerodynamic entrainment,and may cause multiple consecutive resuspension events on the supply-limited surfaces.The dust emission flux of disturbed surface is ten times than that of undisturbed surface,the potential of dust emission is: S2-New tillage>S3-A month after the harrow tillage>S5-Artificial disturbance>S1-No tillage>S4-Crusted surface.The relationship between surface dust emission flux and shear velocity in the measured farmland follows power function distribution.This small device has the advantage of being easy to transport and operate,as well as lower cost,and can be applied to complex terrain that is difficult to access with a field wind tunnel.Comparing with previous wind tunnel experiments and field observations,the device can provide field wind erosion data for the dust emission data set,which is of great significance for the study of dust emission.