4.2 Threshold analysis of the proportion of particulate matter
emissions in wind erosion
The emission of particulate matter in the natural environment is mainly
caused by wind. Under the influence of human activities in farmlands,
when the crust is destroyed, particulate matter emission will increase
significantly (Hoffmann and Funk, 2015). The change in the proportion of
particulate matter emissions in the amount of wind erosion is closely
related to the wind speed (Wiggs and Holmes, 2011). Zhou et al. (2020)
showed that when the wind speed ranges between 6 m/s and -7 m/s, the
dust emission flux can account for 23.60% to 26.58% of the total wind
erosion. It reaches the maximum value, when the wind speed exceeds
approximately 12 m/s. and the proportion of dust emission flux will be
less than 1%. Similar conclusions have been obtained in this study.
Table 3 shows that under low wind speed conditions, the proportion of
particulate matter emissions is the largest. This is because for low
wind speeds it is difficult to transport the larger soil particles in
the BSC, but reach the threshold wind velocity for small particles.
Therefore, the proportion of particulate matter emissions in this stage
is the largest in the total wind erosion. When the wind speed gradually
increases, the soil with a larger particle size will be carried by the
wind and become part of the total wind erosion. At this point, the soil
particles with a large particle size become the main part of the total
wind erosion. If more particulate matter is to be emitted, a process of
mechanical crushing of large-diameter soil particles is required.
However, the soil particles in the BSC are structurally stable and not
easily broken under the action of microorganisms. As a result, the
proportion of particulate matter emissions decreases as the wind speed
increases.
Based on the amount of particulate matter emissions in the total amount
of wind erosion, the amount of wind erosion can be effectively used to
estimate particulate matter emissions (Alfaro et al., 2004). The
correlation between the particulate matter emissions and wind erosion
can effectively predict wind erosion and particulate matter emissions
events (Saxton et al., 2000). BSCs can effectively inhibit wind erosion.
Thus, it is relatively difficult to obtain observational data on the
amount of wind erosion of BSCs. However, the concentration of
particulate matter emitted from the surface can be measured by
instruments, which is relatively easy to obtain. Therefore, it is a rare
but feasible method that uses the particulate matter emission of BSCs to
calculate wind erosion amount. In this calculation process, the
threshold value of the proportion of particulate matter emission in wind
erosion is the parameter to be defined.