Coupling between the atmosphere, trees, and soil via their mass and energy fluxes plays an important role in atmospheric chemistry and physics and forest ecology. Continuous field measurements together with a combination of physico-chemical and biological know-how are essential in order to understand these processes and their diurnal as well as annual dynamics. They give information for spatial scaling-up and for models assessing vegetation dynamics and global change. Here the operation of the SMEAR II station at a Scots pine forest site in Southern Finland is described. The station includes some out-standing set-ups for measurements of aerosol particle size distribution in the size range of 3-500 nm, vertical flux of aerosol particles of diameters down to 12 nm, exchange of trace gases on shoot-scale and soil surface in intervals of 1 minute, spatial distribution of irradiance in the vicinity of a shoot by 800 sensors, spatial distribution of irradiance within the canopy with 200 sensors and two soil catchment areas (890 and 300 m²) for the soil water, dissolved ions and organic carbon balances. Illustrative results concerning the scaling of the canopy photosynthesis by means of the irradiance distribution, the ecosystem water balance deduced from water catchment and stand scale evapo-transpiration measurements and the formation of new particles and vertical transport of them are presented and discussed.