# Atmospheric Charge Separation Mechanism Due to Gas Release from the Crust before an Earthquake
Precursor signals of ionized emissions emerge in geospace 2 to 48 days before an EQ. Atmospheric electrostatic field anomalies prior to EQs have been widely studied. Since the Tangshan EQ in 1976, China has established several atmospheric electrostatic field monitoring stations, and obvious anomalous cases have been observed [14]. [PERSON] et al. [20] noted that anomalous radon emissions trigger considerable decreases in the atmospheric field of the lower atmosphere (from the ground to an altitude of 2 km), as observed around the time of the Kobe EQ in 1995. [PERSON] et al. [20] further suggested that the behavior of radon in terms of the atmospheric electrostatic process could explain seismic precursors observed near the ground. [PERSON] et al. [13] described the characteristics of the vertical atmospheric electrostatic field as negative 7-12 h before an EQ according to the statistics of 30 EQ events of various classes across northern India. [PERSON] [18] reported that more than one hundred cases showed negative E\({}_{\rm z}\) anomalies approximately one day in advance of Ms 4-6 EQs, but there was no obvious relationship between the E\({}_{\rm z}\) value and the epicentral location, similar to that between E\({}_{\rm z}\) and the magnitude. When large amounts of gases are released from the crust into the atmosphere, radioactive elements such as \({}^{222}\)Rn and \({}^{214}\)Th in these gases undergo alpha, beta and gamma decay processes. For example, an alpha particle contains 4.53 MeV of energy, which is sufficient to ionize 1,500,000 gas molecules, because an atmospheric molecule only needs 32 eV of energy for ionization. Therefore, large amounts of positive and negative ions are produced in the atmosphere by radioactive matter originating from the crust. Finally, a unique polarized electric field can be formed in the atmosphere that can alter the direction of the formal background atmospheric vertical electric field [21], as shown in Figure 2. Four  
Figure 1: Background of the global electric circuit (“+”, “-” indicate that Earth’s surface carries negative charges and ionosphere carries positive charges. E\({}_{\rm z}\), j and \(\sigma\) denote the atmospheric electric field, air–earth current and conductivity along the vertical direction, respectively. The bottom-right corner is an example of the daily variation of atmospheric electric field.). cases (the Beijing Ms 3.0, Rongxian Ms 4.7, Changning Ms 6.0, and Wenchuan Ms 8.0 EQs) of preseismic atmospheric electric field hourly scale anomalies are shown in Figure 2, and the time scales for the advancement of the atmospheric electrostatic anomalies are 3.8, 11, 23.5 and 7 h, respectively. How are hourly scale atmospheric electric field anomalies generated before earthquakes? What forces actually cause atmospheric charges to separate, and how are these positive and negative charges separated? The separation of positive and negative charges in the atmosphere is essential for the physical mechanism of preseismic atmospheric electric field formation. In this paper, we present simulation experiments conducted based on these queries.