Rate constants for the gas phase reaction of peroxyacetyl nitrate with selected atmospheric constituents

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Abstract
Rate constants for the removal of peroxyacetyl nitrate (PAN) in the presence of SO2, isobutene, CO, CH3CHO, NO2, H2O, O3 and NO were determined at 296 ± 1°K by monitoring the decay of PAN in excess reactant as a function of time by infrared absorption spectroscopy and/or gas chromatography. The second order rate constants observed were (ppm‐1 min‐1): SO2 < 2 × 10‐8; isobutene < 1 × 10‐6; CO < 2 × 10‐7; CH3CHO (1.1 ± 0.2) x 10‐6; N02 (2.6 ± 1.2) × 10‐6; H2O (3.3 ± 0.5) x 10‐8; O3 = 8 × 10‐5. These reactions with CH3CHO, NO2, and H2O are sufficiently slow so that heterogeneous removal processes for PAN cannot be excluded. For the reaction of PAN with NO, the initial rates of removal of PAN were observed to be first order in PAN concentration and independent of the NO concentration, with a first order rate constant of (1.7 ± 0.5) × 10‐2 min‐1. Possible reaction mechanisms are discussed along with estimates of PAN half‐lives in polluted urban atmospheres.

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