RECENT DEVELOPMENTS IN THE CHEMISTRY AND BIOLOGY OF PEROXYACETYL NITRATE

Peroxyacetyl nitrate (PAN), a ubiquitous compound in ambient air, is f ormed as a secondary product in photochemical reactions of hydrocarbon s in the atmosphere. Although PAN has a relatively short lifetime at r oom temperature (ca. 0.7 h), its thermal dissociation is highly depend ent on the temperature as well as the NO-to-NO2 concentration ratio. T hese 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 s ubstantial transport and redistribution of reactive nitrogen compounds in the atmosphere. In urban atmospheres, PAN concentrations in the pa rt-per-billion range can lead to plant damage, while the potential hum an 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. S tudies 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 dissoc iation reaction of PAN and associated reactions of the acetylperoxy ra dical; measure atmospheric abundances; and determine biological effect s. In the present paper, many notable aspects of these topics are revi ewed and integrated to allow a fundamental understanding of the import ance of this molecule.