Bimodal variation in mercury wet deposition to the coastal zone of the southern Baltic

Abstract. In the following periods: November 2005–June 2006 and October 2007–January 2009, concentrations and deposition rates of total mercury (THg) and Hg(II) were measured in precipitation over the urbanized and industrialized area of the southern Baltic – the city of Gdynia. Rains over the coastal zone had different concentrations of total mercury, they ranged from 8.6 to 118.0 ng L⁻¹, out of which about 32% were labile, inorganic forms, easily reducible in a SnCl₂ solution. Over the southern Baltic two maxima of concentrations were observed: first, in the heating season and second, in the non-heating season. Elevated concentrations of mercury in precipitations during heating seasons were the result of the activity of local emission sources (intensive combustion of fossil fuels in domestic furnaces and individual power and heat generating plants). During the warm season, precipitation over the southern Baltic could clean the air from Hg reemitted from sea and land surfaces. Precipitations, which purified marine and continental air masses were responsible for the comparable input of mercury to the coastal zone. The wet deposition value in 2008 was estimated to be 28.9 μg m⁻². In the coastal zone of the southern Baltic, acid precipitations with the elevated Hg concentrations are very frequent.