1 Worldwide atmospheric mercury measurements: a review 1 and synthesis of spatial and temporal trends 2

Abstract 10 A large number of activities have been carried out during the last decade in different regions 11 of the world, including polar regions, aiming to assess the level of mercury (Hg) species in 12 ambient air and in precipitation observing their variation over time and with changing 13 meteorological conditions. Following the discovery of atmospheric Hg depletion events 14 (AMDEs) in Polar Regions several studies have indeed been conducted in order to assess the 15 chemical-physical mechanisms related to AMDEs occurred in polar atmospheres with special 16 attention to the consequences of these phenomena in terms of contamination of polar 17 environment due to the rapid conversion of atmospheric gaseous Hg (Hg0) into reactive and 18 water-soluble forms that may potentially become bioavailable. The understanding of the way 19 in which mercury released to the atmosphere is eventually incorporated into biota is of crucial 20 importance not only for the polar regions but also for the marine environment in general. The 21 world's oceans and seas are in fact both sources and sinks of Hg playing an important role into 22 the Hg cycle. In order to investigate both large-scale (spatial) and short/long-term (temporal) 23 distribution characteristics of atmospheric mercury on global scale, we have analyzed the Hg 2