Abstract
Abstract. Cold surge (CS) is considered a favorable weather process to improve air quality and is widely recognized. However, there is no detailed study on the differences in the dispersion ability of different types of CSs in relation to haze days in eastern China (HDEC). This paper uses the hierarchical clustering algorithm to classify the cool-season (November to February of the following year) CSs across eastern China into blocking CSs and wave-train CSs and compares their influences on the number of HDEC from 1980 to 2017. Results show that the wave-train CSs can significantly improve the visibility in eastern China and generally improve air quality for about 2 d longer than the blocking CSs, which indicates that the blocking CSs have a weaker ability to dissipate HDEC compared with the wave-train CSs. The CSs affect the HDEC by changing meteorological elements like thermal inversion potential, horizontal surface wind, sea level pressure (SLP), and surface air temperature (SAT). A period of 4 d after the outbreak of CSs, the variations of thermal inversion potential and horizontal surface wind of two types of CSs tend to be consistent. However, the negative SAT anomalies and the positive SLP anomalies caused by the blocking CSs lasted shorter than those caused by the wave-train CSs, forming favorable conditions for the rapid growth of HDEC. Furthermore, results show that in recent years, especially after the 1990s, the frequency of wave-train CSs has decreased significantly, while the frequency of blocking CSs has slightly increased, indicating that the overall ability of CSs to dissipate HDEC has weakened in general. This work may provide reference for the future formulation of haze control policies in East Asia.
Highlights
Haze in eastern China is generally referred to as the polluted particulate aerosols suspended in the air (Yin et al, 2019) and can reduce visibility and affect traffic and ecological sustainability (Xu et al, 2013; Xie et al, 2014; Wang et al, 2016)
This paper investigates the connection between the Cold surge (CS) and the cool-season haze over the eastern region of China (EC) based on the observational and reanalysis datasets from 1980 to 2017
The blocking CSs are accompanied by a meridional dipole in the upper tropospheric geopotential height (GPH) anomalies, which consists of a stable blocking structure
Summary
Haze in eastern China is generally referred to as the polluted particulate aerosols suspended in the air (Yin et al, 2019) and can reduce visibility and affect traffic and ecological sustainability (Xu et al, 2013; Xie et al, 2014; Wang et al, 2016). Wang et al (2016) proposed that the “early in the north and late in the south” feature of air quality improvement in mainland China results from the cold air masses moving southward from high latitudes to low latitudes after the outbreak of CSs. some studies have shown that the weakening of the East Asian winter monsoon and global warming leads to the decrease of CSs (Qu et al, 2015; Wang and Ding, 2006), extreme low-temperature events are still frequent (Park et al, 2011a), which means the assessment of the haze dispersion capacity of cold air activities is still full of uncertainty.
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