The properties of vertical electric field during haze event in Xi'an, China

Abstract

This paper analyses the characteristics of vertical electric field (Ez) fluctuations and their correlation with other quantities during haze event in Xi'an, China. Our results indicate that in regard to long-period fluctuations (period > 30 min), when the RH (relative humidity) change rate is positive at the development stage of haze event, secondary chemical reactions increase the PM10 (particulate matter 10 μm or smaller in diameter) concentration. When the charge properties of particles are different, three types of spatial electric field changes occur. When the RH change rate is negative, if both the PM10 concentration and absolute value of Ez decrease, this suggests that the haze event has entered the dissipation stage. If the PM10 concentration and Ez do not change notably over time, this indicates that no secondary chemical reactions occur, and no new particles are produced. Regarding short-period fluctuations, Ez fluctuations with a period longer than 100 s notably contribute to the overall Ez fluctuations, and the Ez fluctuations exhibit a good correlation with the RH and PM10 concentration. In addition, Ez fluctuations with a period shorter than 30 s yield an important contribution to the overall Ez fluctuations, but the correlation between Ez fluctuations and the RH and PM10 concentration is poor, which indicates that Ez fluctuations with a period shorter than 30 s are not caused by RH variation. These results are of great significance to the identification of pollutant gases during haze periods and the prevention and control of haze events.