Abstract. The North Atlantic Oscillation (NAO) has been confirmed to be closely related to the weather and climate in many regions of the Northern Hemisphere; however, its effect and mechanism upon the formation of dust events (DEs) in China have rarely been discussed. By using the station observation dataset and multi-reanalysis datasets, it is found that the spring dust aerosols (DAs) in North China (30–40∘ N, 105–120∘ E), a non-dust source region, show high values with a strong interannual variability, and the spring DAs in North China are significantly correlated with the previous winter's NAO. According to the nine spring DEs affected significantly by the negative phase of the preceding winter's NAO in North China during 1980–2020, it is shown that before the outbreak of DEs, due to the transient eddy momentum (heat) convergence (divergence) over the DA source regions, the zonal wind speed increases in the upper-level troposphere, strengthening the zonal wind in the middle–lower levels through momentum downward transmission. Simultaneously, there is transient eddy momentum (heat) divergence (convergence) around the Ural Mountains, which is favorable for the establishment and maintenance of the Ural ridge, as well as the development of the air temperature and vorticity advections. The combined effects of temperature and vorticity advections result in the Siberian Highs and Mongolian cyclone to be established, strengthen, and move southward near the surface, guiding the cold air from high latitudes southward, and is favorable for the uplift and transmission of DAs to North China downstream. Simultaneously, the changes in upstream transient eddy flux transport can cause both energy and mass divergence in North China, resulting in diminishing winds during DEs, which would facilitate the maintenance of dust aerosols here and promote the outbreak of DEs. This study reveals the impact of transient eddy flux transport on the dusty weather anomalies modulated by the NAO negative signal in North China, which deepens the understanding of the formation mechanism of DEs in China.

Mercury (Hg) is a neurotoxic pollutant ubiquitously present in the environment (Obrist et al., 2021). Atmospheric Hg cycling is a crucial component of biogeochemical Hg cycling, owing to the extreme volatility of Hg (Sommar et al., 2020). Atmospheric Hg consists of a gaseous, elemental, and dominant type (Hg 0 ; approximately 95%), and a gaseous or particulate divalent type (Hg II ) (Lindberg & Stratton, 1998). Owing to its low chemical reactivity and water solubility, Hg 0 has a long lifespan in the troposphere (0.8-1.3 a) (Saiz-Lopez et al., 2018). It can be transported globally through atmospheric circulation before being adsorbed by vegetation and soils through dry deposition (Gustin et al., 2008;Wright et al., 2016) or transformed into Hg II , which is easily removed by wet deposition (Lyman et al., 2020). Deposited Hg potentially poses risks to wildlife and humans owing to its methylation and bioaccumulation characteristics (Roman et al., 2011;Zhang et al., 2010Zhang et al., , 2021.Seasonality of atmospheric Hg concentrations has been observed at multiple ground-based monitoring sites worldwide. In particular, the observed seasonality is stronger in the temperate Northern Hemisphere, which includes forest, coastal, and urban sites (

Observations show that summer precipitation in China has undergone pronounced changes, resulting in an enigmatic “north‐south drying‐wetting” pattern in eastern China that is of great concern for socio‐economic development. Scientific consensus on the mechanisms that are responsible for this pattern of change has not yet been achieved. We show that this complex pattern of summer total precipitation trends observed in China since the 1960s is overwhelmingly the result of changes in daily precipitation frequency, rather than being the result of changes in precipitation intensity or the frequency of synoptic circulation patterns favorable to precipitation. Changes in precipitation intensity, which are very likely due to anthropogenic greenhouse gas forcing, contribute a relatively homogeneous wetting tendency across the country while changes due to synoptic circulation change are weak. The changes in daily precipitation frequency that drive the observed patterns of change may be due to aerosols, but improved process understanding will be required to resolve that question and enable reliable projections of regional scale precipitation change in China and elsewhere.