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The Col Margherita (MRG) Observatory is a high-altitude background station located in the Eastern Italian Alps. Its elevation and distance from major anthropogenic and natural sources make it ideal for monitoring baseline mercury levels and investigating its geochemical cycles. In this work, total gaseous mercury (TGM), ozone (O 3) and meteorological variables were studied to investigate seasonal and diurnal variability of TGM measurements from March 2018 to May 2019. We found that the year-round mean TGM concentration was 1.8 times higher than the annual atmospheric mercury measurements previously reported during the GMOS project at the same measurement site. The seasonal variation of TGM was characterized by high values in spring and summer and lower values in winter. A systematic diel pattern of TGM was obtained, with low concentrations during the daytime and higher concentrations in the late evening. Spatial patterns and temporal changes in TGM, back-trajectories (BTs) and planetary boundary layer (PBL) analysis showed that total gaseous mercury levels were influenced by local meteorology, as well as regional and long-range transport of air masses. The lowest TGM concentrations in winter are associated with high wind speeds, low boundary layer height and cleaner air masses originating from the Western sector. Conversely, the highest TGM concentrations in spring and summer were attributed to polluted air masses passing over North-eastern and Continental Europe and were probably favoured by the higher PBL height. During the snow cover season, investigation of TGM peak events also demonstrated the potential influence of re-emission processes of previously reactive mercury deposition over snow surfaces. [Display omitted] • A one-year record mean TGM concentration at the MRG was higher than other long-term values observed in remote mountain sites. • TGM was characterized by high values in spring and summer and lower values in winter. • A diel trend of TGM was observed, with low concentrations in the daytime and higher concentrations in the late evening. • TGM levels were influenced by local meteorology, as well as regional and long-range transport of air masses. • Analysis of specific atmospheric mercury elevated events (AMEEs) was performed. [ABSTRACT FROM AUTHOR]

Mercury (Hg) and its compounds have long been known to be toxic to human health and theenvironment1,whilst ozone (O3) is highly relevant to the Earth’s climate, ecosystems and humanhealth2.Measurements of Hg and O3 in alpine environments are pivotal when evaluatingair quality in natural ecosystems as well as when trying to understand regionaland synoptic atmospheric transport regimes and advection of air pollutant to theAlps3.This study is crucial for the evaluation of the Hg exchange processes between soil andatmosphere in a high altitude alpine environment, where increasing Hg snowpack concentrationsoccur during winter time, followed by Hg release to the overlying atmosphere during spring andsummer4 timesnowmelt events. In this context, evaluating the gas phase reaction between elemental mercury andozone5is essential. All the experimental activities were performed at the CNR-IDPA atmosphericobservatory at Col Margherita (CMA) that is located in the Italian southeastern Alps, aUNESCO protected region far from anthropogenic and natural sources of air pollutants(altitude 2543 m a.s.l., 46˚ 22’0.6" N, 11˚ 47’30.9" E). The observatory is equipped with acomplete weather station. Total Gaseous Mercury (TGM) was measured from March toAugust 2018 using a Tekran 2537B (Tekran Inc.), a mercury analyzer that alternately samplesTGM on two gold traps and determines it using cold vapor atomic fluorescence spectrometry(CVAFS). During the same period, near-surface O3 measurements were performed with aThermo 49c UV photometric analyzer (Thermo Corp.), according to WMO/GAW guidelines.For the purpose of the present study, daily and monthly levels of hourly Hg and O3concentrations were assessed. Relationships with meteorological parameters (T, RH, P,WS, WD, solar radiation, snow) were investigated by performing a back trajectoryatmospheric reanalysis using HYSPLIT for the duration of the measurement campaign.The results showed that Hg concentrations increase, on average, from spring tosummer, with some episodes of rapid daytime increase or decrease of atmospheric Hgthat could be related to both the O3 variability and specific weather conditions. [ABSTRACT FROM AUTHOR]