Peroxyacetyl nitrate in long-range transported polluted air

Abstract

The action of sunlight on air polluted with organic compounds and nitrogen oxides leads to a very complex mixture of reaction products1,2. Peroxyacetyl nitrate (PAN) seems to be the most useful indicator of photochemically polluted air2–5 and was monitored during the summer of 1980 at Riso, a rural area, in Denmark and in Goteborg in Sweden (Fig. 1). These measurements seem to be the most northerly (56–58 °N) observations of PAN ever made. The long-range transport of ozone and of visibility-reducing aerosols has been observed on several occasions7–12. In southern Scandinavia this is called a ‘white episode’9. The measurements reported here reveal that high PAN levels occur during this type of episode. The comparison of these levels with those observed in optimal conditions for formation of PAN from local sources indicated that long-range transport contributes substantially to the presence of PAN in southern Scandinavia.