Monitoring experiments of soil air in column show that relative humidity (RH) of air in the soil of the Loess Plateau fluctuates with atmospheric pressure (AP), which is barometric pumping resulting in the vertical movement of soil air and the change of its RH. When AP increases, soil air is compressed and atmospheric air enters the soil, causing RH to decrease. When AP decreases, soil air expands and rises, causing the flow of moist air outwards from the soil and increasing RH. Therefore, RH fluctuates reversely with AP (the correlation coefficient between RH and AP can reach –0.74). This paper studies the effect of barometric pumping on RH in the loessal soil of the Loess Plateau, and reveals the mechanism responsible for the vertical movement of soil air. On a yearly timescale, the volume of soil air expands with a general decrease in AP from January to July, then compresses with an increase in AP from July to December. On a daily timescale, the air in soil shows bimodal fluctuations. Barometric pumping is the driving force underpinning the soil air movement, and therefore dominating its fundamental characteristics. From a preliminary establishment of model calculation, the volume of soil air movement occurring in the Loess Plateau is proportional to the amplitude of AP fluctuations, aerated porosity, and thickness of the local loess layer. The amplitude of air fluctuations in the soil is independent from the aerated porosity.

柱内土壤空气监测实验表明，黄土高原土壤中空气的相对湿度（RH）随大气压（AP）的变化而波动，这是气压泵送，导致土壤空气的垂直运动及其相对湿度的变化。当 AP 增加时，土壤空气被压缩，大气进入土壤，导致 RH 降低。当 AP 减少时，土壤空气膨胀和上升，导致潮湿空气从土壤向外流动并增加 RH。因此，RH随AP反向波动（RH与AP的相关系数可达–0.74）。本文研究了气压泵对黄土高原黄土土壤相对湿度的影响，揭示了土壤空气垂直运动的机理。在每年的时间尺度上，1-7月土壤空气体积随着AP的普遍减少而膨胀，7-12月随着AP的增加而压缩。在每日时间尺度上，土壤中的空气呈现双峰波动。气压泵是支撑土壤空气运动的驱动力，因此支配了其基本特征。初步建立模型计算可知，黄土高原发生的土壤空气运动量与AP波动幅度、充气孔隙度和局部黄土层厚度成正比。空气波动幅度 因此支配了它的基本特征。初步建立模型计算可知，黄土高原发生的土壤空气运动量与AP波动幅度、充气孔隙度和局部黄土层厚度成正比。空气波动幅度 因此支配了它的基本特征。初步建立模型计算可知，黄土高原发生的土壤空气运动量与AP波动幅度、充气孔隙度和局部黄土层厚度成正比。空气波动幅度土壤中的孔隙度与充气孔隙度无关。