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Journal of Arid Land
Journal of Arid Land  2022, Vol. 14 Issue (6): 589-603    DOI: 10.1007/s40333-022-0066-0
Research article     
Separating emitted dust from the total suspension in airflow based on the characteristics of PM10 vertical concentration profiles on a Gobi surface in northwestern China
ZHANG Chunlai1, WANG Xuesong1,2,*(), CEN Songbo1, ZHENG Zhongquan Charlie3, WANG Zhenting4
1State Key Laboratory of Earth Surface Processes and Resource Ecology, MOE Engineering Research Center of Desertification and Blown-sand Control, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China
2School of Environment, Beijing Normal University, Beijing 100875, China
3Aerospace Engineering Department, University of Kansas, Lawrence, KS 66045-7621, USA
4Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
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Abstract  

During aeolian processes, the two most critical factors related to dust emissions are soil particle and aggregate saltation, which greatly affect the vertical profiles of near-surface dust concentrations. In this study, we measured PM10 concentrations at four different heights (0.10, 0.50, 1.00 and 2.00 m) with and without continuous and simultaneous aeolian saltation processes on a Gobi surface in northwestern China from 31 March to 10 April, 2017. We found that the vertical concentration profiles of suspended PM10 matched the log-law model well when there was no aeolian saltation. For the erosion process with saltation, we divided the vertical concentration profiles of PM10 into the saltation-affected layer and the airflow-transport layer according to two different dust sources (i.e., locally emitted PM10 and upwind transported PM10). The transition height between the saltation-affected layer and the airflow-transport layer was not fixed and varied with saltation intensity. From this new perspective, we calculated the airflow-transport layer and the dust emission rate at different times during a wind erosion event occurred on 5 April 2017. We found that dust emissions during wind erosion are primarily controlled by saltation intensity, contributing little to PM10 concentrations above the ground surface compared to PM10 concentrations transported from upwind directions. As erosion progresses, the surface supply of erodible grains is the most crucial factor for saltation intensity. When there was a sufficient amount of erodible grains, there was a significant correlation among the friction velocity, saltation intensity and dust emission rate. However, when supply is limited by factors such as surface renewal or an increase in soil moisture, the friction velocity will not necessarily correlate with the other two factors. Therefore, for the Gobi surface, compared to limiting dust emissions from upwind directions, restricting the transport of suspended dust in its path is by far a more efficient and realistic option for small areas that are often exposed to dust storms. This study provides some theoretical basis for correctly estimating PM10 concentrations in the Gobi areas.

Key words： PM10      vertical concentration profiles      dust emission rate      saltation intensity      suspensions      Gobi surface     
Received: 11 February 2022      Published: 30 June 2022
Corresponding Authors: WANG Xuesong     E-mail: xswang@bnu.edu.cn
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ZHANG Chunlai
WANG Xuesong
CEN Songbo
ZHENG Zhongquan Charlie
WANG Zhenting
Cite this article:

ZHANG Chunlai, WANG Xuesong, CEN Songbo, ZHENG Zhongquan Charlie, WANG Zhenting. Separating emitted dust from the total suspension in airflow based on the characteristics of PM10 vertical concentration profiles on a Gobi surface in northwestern China. Journal of Arid Land, 2022, 14(6): 589-603.

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http://jal.xjegi.com/10.1007/s40333-022-0066-0     OR     http://jal.xjegi.com/Y2022/V14/I6/589

Fig. 1 Layout of the study site and the used instruments. (a), rotating-cup anemometers; (b), aerosol monitors; (c), automatic weighing sand traps.
Fig. 2 Observed relationship between normalized concentration (c/cr) and normalized height (z/zr). (a), 10 min average data for 20 h; (b), the overall average data with error bars. c is the mean PM10 concentration at height z, and cr is the PM10 concentration at reference height zr. Regression equations that fit both the power and logarithmic regression models are shown.
Fig. 3 Relationship between regression coefficient (b) for the profile in Equation 9 and friction velocity (u*)
Fig. 4 Observations of the u* (a), PM10 concentration (c) values at heights of 0.10, 0.50, 1.00 and 2.00 m (b, c, e and f, respectively), and sand flux (Q) at 0.05 m height (d) during wind erosion event between 14:08 and 18:08 (LST) on 5 April 2017. All values were 1 min averages, and PM10 concentration data between 16:03-16:08 were missing.
Fig. 5 Verification of the vertical profile of the u* using the 10 min average suspension concentrations above the saltation-affected layer (heights of 1.00 and 2.00 m). b is the regression coefficient.
Time (min) Saltation Suspension TSA (m) u* (m/s)
m n b c(1)
91-100 0.282 -2.195 -0.033 0.061 0.58 0.267
101-110 0.322 -2.176 -0.029 0.064 0.66 0.295
111-120 0.408 -3.064 -0.037 0.052 0.56 0.292
121-130 0.288 -1.872 -0.042 0.071 0.61 0.304
131-140 0.232 -1.610 -0.032 0.070 0.62 0.280
141-150 0.430 -2.359 -0.040 0.072 0.67 0.297
151-160 0.376 -2.381 -0.036 0.058 0.70 0.309
161-170 0.463 -1.882 -0.040 0.098 0.77 0.312
171-180 - - -0.029 0.058 <0.50 0.305
181-190 - - -0.034 0.061 <0.50 0.292
191-200 - - -0.035 0.059 <0.50 0.309
201-210 - - -0.032 0.057 <0.50 0.288
211-220 - - -0.029 0.062 <0.50 0.281
221-230 - - -0.032 0.067 <0.50 0.276
231-240 - - -0.035 0.090 <0.50 0.299
Table 1 Parameters associated with dust emissions during the wind erosion event on 5 April 2017
Erosion event Particle size composition (%) Mean particle size (μm)
<2 μm 2-63 μm 63-250 μm 250-500 μm 500-2000 μm >2000 μm
Before the erosion event 1.9 13.3 48.0 5.2 11.2 20.6 708.1
After the erosion event 1.4 12.2 45.6 4.1 20.8 15.8 709.6
Table 2 Particle size composition of the surface sediments before and after the erosion event on 5 April 2017
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