The relationship between ozone, peroxyacetylnitrate and precursors in long range transport of photooxidants to Scandinavia

Abstract. The concentration of NO2 made up the major fraction of the sum of the concentrations of NO2, PAN and HNO3 + NO3- in the measurem ents at f rural Scandinavian sites during August-October 1989. There was significant positive correlation between ozone and PAN in August but not in October. Atmospheric boundary layer chemistry and transpor t model calculations show that in August and September there is consi derable chemical degradation of precursors and (photo)chemical genera tion of secondary products like O3 and PAN during transport from the source regions in continental Europe to Scandinavia, while in October the contribution from chemical processes to the change in precursor concentration is usually minor. Only 5% or less of the surface NOx em issions are calculated to reach the free troposphere above the bounda ry layer as NOx.