In this volume, the Camnission of the Eurc.pean camunities presents the proceedissJs of the secood Eurc.pean Synpositun en the physioo-chemical behaviour of atIoospheric pollutants. '!bese Symposia are organized in intervals of about t'110 years wi thin the framework of a Concerted Action in this area, which is part of the CCIIlIlIll1ities' research progranure in the environmental field. '!be Eurc.pean CCIIlIlIll1ities co-operate in this area wi th Eurc.pean Non-Member States under an agreement within the frame'llOrk of coor (~ration Scientifique et Technique). This Jlgreement (COOT Project 61a bis) has been signed by the European Communities, Austria, Switzerland, Sweden and Yugoslavia. 'lbe scc.pe of the Concerted Actien is to co-onHnate all research in the area executed in the participatissJ countries and to collect and dissemi- nate the results. The research inventory established comprises 165 individual projects~ regular meetings of 5 WorkissJ Parties permit close contacts amossJst the scientists involved. 'lbe Eurc.pean Syrrposia should pennit fran time to time an overall review of the progress.'lbe first Symposium held in October 1979 *) permitted to review the state of progress at the beginning of the Concerted Actien. The second Symposium gives now an overview of the important achievements durissJ the past two years. These are evident already fran the number of contri- butions which increased from 45 in 1979 to 74 in 1981. The results collected durissJ this per iod permi tted the presentation of a number of important review papers.