The PMK Network is part of the national network for deposition measurements. The aim is a longterm monitoring concentration and deposition of different air transported compounds. The aim is also to generate knowledge about longterm variation in the deposition field, and to give background data from low polluted areas for calculation of pollution deposition in more polluted areas. The Air and Precipitation Chemistry Network includes about 25 sites (14 in northern Sweden) where precipitation from open accumulating samplers are collected and analyzed for pH, SO4, NO3, NH4, Cl, Ca, Mg, Na, K, conductivity, and amount of precipitation (Table 4, #1.2). At 3 sites (one in northern Sweden) precipitation is analyzed for heavy metals, mercury, and methyl-mercury (Table 4, #1.3).