Establishing a national network for atmospheric mercury monitoring: preliminary spatial and temporal insights from Italy

In compliance with European air quality regulations and the Italian “Reti Speciali” agreement, a dedicated network of three strategically positioned monitoring stations was established in 2012. Designed to account for geographical variability, this network enabled the first coordinated sampling campaigns for atmospheric mercury (Hg) data in ambient air and deposition. The resulting representative nationwide data, collected from 2020 to 2023, enabled the detection of seasonal, temporal, and spatial variations, which are analyzed in this study. Throughout the observational period, atmospheric Hg levels varied among the stations, exhibiting annual mean values between 1.22 ± 0.25 and 2.01 $\pm 0.42{\mathrm{ng/m}}^3$. A notable decrease in concentrations was evident in the northern and central regions. Conversely, the southern station maintained relatively stable levels, likely attributable to the predominant influence of natural sources. Ambient air Hg concentrations were examined for the impact of potential sources, with analysis conducted at both synoptic and local scales. Long-range transport pathways were identified using Potential Source Contributing Function (PSCF) analysis, while local investigations incorporated meteorological parameters, ozone measurements, and nearby fire hot-spot data. Analysis of samples from Hg deposition monitoring campaigns (2021 - 2023) revealed total mercury deposition values below 20 ${\mathrm{ng/m}}^{2}d$. These efforts, which involved four sampling sessions per year at each station, showed that seasonal variations were primarily influenced by rainfall patterns.