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

The concentration of N02 made up the major fraction of the sum of the concentrations of N02, PAN and HNO3 + NO3− in the measurements at five 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 transport model calculations show that in August and September there is considerable chemical degradation of precursors and (photo)chemical generation 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 emissions are calculated to reach the free troposphi;re above the boundary layer as NOx.