Thermal decomposition pathways for peroxyacetyl nitrate (PAN): Implications for atmospheric methyl nitrate levels

The unimolecular decomposition pathways of peroxyacetyl nitrate (PAN) have been investigated in the presence of added NO ₂ over the temperature range 298-345 K. The major products of the PAN decomposition were CO ₂ and, depending on the ratio of O ₂ to NO ₂ in the experiment, either CH ₂O or methyl nitrate. From the observed PAN decay rates and product yields, upper limits for the direct formation of either NO ₃ or methyl nitrate from the unimolecular decay of PAN were obtained. The results indicate that these channels occur with rate constants that are thousands of times slower than dissociation of PAN into peroxyacetyl and NO ₂, and that PAN decomposition is not a significant source of atmospheric methyl nitrate.