Current and past mercury distribution in air over the Idrija Hg mine region, Slovenia

Mercury in air over the Idrija region, where the worldʹs second largest mercury (Hg) mine is located, decreased significantly in the last decade, from more than 20,000 ng m−3 in the early 1970s to values below 100 ng m−3 in the 1980s, and finally reached a level of 10 ng m−3 or even lower at the summer of the year 2004. The air concentration of Hg was continuously monitored after closure of the Hg mine. Hg0 in air was mapped in November 2003 at over 100 locations in the Idrija region during a 3-day period under different weather conditions, and the concentrations found were between 2.5 to over 2000 ng m−3. The Hg concentration in air was mostly below 10 ng m−3. The highest values were observed in the near vicinity of the former smelting plant, as well under its chimney. Elevated concentrations were also observed at some other locations in Idrija town. Mercury evaporation from topsoil was measured continuously for a 24 h period at two heavily polluted locations in Idrija and 50 km downstream the River Idrijca at Bača pri Modreju. The average Hg concentration in air at Bača pri Modreju was 5.5 ng m−3, with an average Hg flux from soil to atmosphere of 34 ng m−2 h−1. At the site in Idrija the average Hg concentration in air was 11 ng m−3 with an average Hg flux from soil to the atmosphere of 84.4 ng m−2 h−1.