Currently (2016) air concentrations are measured at 20 sites, bulk deposition at 32 sites, throughfall deposition at 54 sites, dry deposition at 10 sites and soil water chemistry at 56 sites within SWETHRO.
Air concentration diffusive samples, as well as samples of throughfall and bulk deposition, are collected monthly throughout the year. Soil water samples are collected three times a year, to represent the conditions before (Feb-May), during (Jun-Sep) and after the vegetation period (Sep-Dec).
Monitoring sites are positioned in closed, mature managed forests with no major roads or other pollution sources in the vicinity. Relatively homogenous locations, with regard to topography and tree density, are chosen. The bulk deposition as well as the air concentration measurements are positioned in an open area close to the throughfall sites, preferably with similar topographical properties. Many sites have been replaced with new sites, in the vicinity of the old site, due to an ageing forest and subsequent harvests. The new sites were assigned a new identity.
At some sites, additional data are available, such as tree growth, needle chemistry, vegetation and meteorology.