A mass balance model lo calculate critical loads of' airborne acidity and cutrophication to forest ecosystems has been computerized. The SONOX soliware developed at the Institute of Environmental Protection replicates the sequence of' events on the path from sulfur and nitrogen emission through their deposition and next overlaying it on critical loads values lo identify the extent and areas of critical loads cxcccdance. To support decision making a converse direction is offered to assess the necessary emission reductions lo meet assumed environmental goals by eliminating or suitably abating the critical loads cxcccdance. This software originally developed and applied to support the Polish contribution lo the negotiations of the Oslo and Gothenburg Protocols or the Convention on Long-Range Transboundary Air Pollution was thereafter used to assess the capacity of achieving the, interim environmental quality targets ofthe NEC Directive in Poland, to support the development of air protection programs lor administrative units exposed to transboundary lluxcs and other decision making purposes.