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 NO2 over the temperature range 298-345 K. The major products of the PAN decomposition were CO2 and, depending on the ratio of O2 to NO2 in the experiment, either CH2O or methyl nitrate. From the observed PAN decay rates and product yields, upper limits for the direct formation of either NO3 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 NO2, and that PAN decomposition is not a significant source of atmospheric methyl nitrate.