Relationships between Low-Level Jet and Low Visibility Associated with Precipitation, Air Pollution, and Fog in Tianjin

Abstract

In this study, relationships between low-level jet (LLJ) and low visibility associated with precipitation, air pollution, and fog in Tianjin are investigated based on observational data from January to December, 2016. Statistical results show 55% of precipitation is accompanied by LLJ, and two causes responsible for the relatively high percentage are presented. The result of case analysis shows that some southwesterly LLJs are favorable for the formation of precipitation by transporting water vapor when the water vapor channel from the South China Sea or Bengal Bay to Bohai Rim region is established. Statistical results show 55% of pollution episodes (PEs) are accompanied by LLJs. When pollutions are observed in the southern industrial regions, nocturnal southwesterly LLJ, which can carry polluted air masses from polluted regions to Tianjin and induce turbulent mixing, can enhance surface PM2.5 concentration and is favorable for the formation of surface pollution at night. Nocturnal northerly or southeasterly LLJ leads to clear air masses mixing with polluted air masses and is favorable for increasing visibility. Contributions of southwesterly LLJs to the formation of fog and precipitation are similar, which both rely on establishing the water vapor channel despite occurrence heights of LLJs being different.

Impacts of Boundary-Layer Structure and Turbulence on the Variations of PM2.5 During Fog–Haze Episodes

“…There were obvious negative correlations between visibility and RH as well as surface PM 2.5 mass concentration (Fig. 2a1, a2, c1, c2) during the two cases, which confirms that low visibility in Tianjin is closely related to the occurrence of fog-haze (Ye et al 2015b;Ju et al 2020a).…”

“…3d2). The fog persisted for the whole day with the aid of moist advection (Tian et al 2019;Ju et al 2020a). Finally, the Tianjin region was affected by an anticyclone in the north-western region (Fig.…”

“…Previous literature has reported that the economic and human losses associated with fog events are comparable to those caused by tornadoes and even hurricanes and winter storms (Gultepe et al 2007), and fog events have caused costly and even catastrophic events in China. Haze and fog frequently and simultaneously occur in the NCP (Ju et al 2020a); thus, much attention should be paid to fog-haze events (Fu et al 2014).…”

Low-level jets and their implications on air pollution: A review

“…In addition, the transport of precursors and moisture by the LLJs facilitates the formation of pollution periods. In the North China Plain, southwesterly LLJs establish a moisture channel from the South China Sea to the Bohai Rim Region, contributing to the frequent PM 2.5 events in winter (Ju et al, 2020).…”

Study on the atmospheric water vapor based on laser-induced breakdown spectroscopy

“…6 The water-soluble substances could expand their pollution scope during the process of atmospheric water vapor circulation. 7 Some air pollutants may combine with water vapor and become more toxic. For example, sulfur dioxide reacts with water vapor to form sulfuric acid or other sulfides, which can eventually cause acid rain.…”