EVIDENCE FOR FORMATION OF A PAN ANALOG OF PINONIC STRUCTURE AND INVESTIGATION OF ITS THERMAL-STABILITY

The first evidence and laboratory study of a peroxyacetyl nitrate (PAN ) analogue produced by the photooxidation of a terpene, alpha-pinene, is presented. This PAN analogue, assigned to 3-acetyl-2,2-dimethyl-cyc lobutane-acetyl peroxynitrate and referred to as ''alpha-pinonyl perox ynitrate'' (alpha P-PAN) was synthesized in the gas phase from the rad ical (OH, Cl, Br, or NO3) initiated oxidation of pinonaldehyde (3-acet yl-2,2-dimethyl-cyclobutyl-ethanal) in the presence of excess NO2 and evidenced by Fourier transform-infrared (FT-IR) spectroscopy. Another reaction channel producing PAN was also observed for some of the radic al initiators. Of particular atmospheric interest, the experiments wit h OH radicals demonstrated that alpha P-PAN is the main product of pin onaldehyde under NOx-rich conditions with a yield of (81.3 +/- 16)%, w hile an upper limit of the PAN yield for this reaction is around 8%. T he further photooxidation of alpha P-PAN was also observed to produce PAN directly. The thermal stability of alpha P-PAN was studied between 303 and 281 K. The rate constant of thermal dissociation was found to be k(-1) = 10((9.25+/-0.33)) x exp [-(72.0 +/- 1.9)/RT] where the act ivation energy is in kJ mol(-1). Distortions of the kinetic profiles a ttributed to aerosol formation were observed and led to large errors i n the above estimation of k(-1). Within the uncertainties, the observe d thermal stability of alpha P-PAN is comparable to that of PAN. The t ropospheric importance of pinonaldehyde and of alpha P-PAN are discuss ed.