RECENT DEVELOPMENTS IN THE CHEMISTRY AND BIOLOGY OF PEROXYACETYL NITRATE

Peroxyacetyl nitrate (PAN), a ubiquitous compound in ambient air, is formed as a secondary product in photochemical reactions of hydrocarbons in the atmosphere. Although PAN has a relatively short lifetime at room temperature (ca. 0.7 h), its thermal dissociation is highly dependent on the temperature as well as the NO-to-NO2 concentration ratio. These factors lead to a relatively long lifetime for PAN in the mid to upper troposphere, where temperatures are much lower than temperatures at the earth's surface. The longer lifetime at this altitude allows substantial transport and redistribution of reactive nitrogen compounds in the atmosphere. In urban atmospheres, PAN concentrations in the part-per-billion range can lead to plant damage, while the potential human health effects at these concentrations are currently unknown. These aspects of the chemistry and biology of PAN have led to considerable research into the properties, analysis, reaction kinetics, atmospheric concentrations, and biological effects during the past dozen years. Studies have been conducted that reexamine the infrared and ultraviolet spectra of PAN, the deposition velocity under a variety of conditions, its hydrolysis in acidic and basic solutions, and the thermal dissociation reaction of PAN and associated reactions of the acetylperoxy radical; measure atmospheric abundances; and determine biological effects. In the present paper, many notable aspects of these topics are reviewed and integrated to allow a fundamental understanding of the importance of this molecule.