Photo-oxidation of pinonaldehyde at low NO_x: from chemistry to organic aerosol formation

Abstract. Pinonaldehyde oxidation by OH radicals under low-NO_x conditions produces significant secondary organic aerosol (SOA) mass yields. Under concurrent UV illumination, mass yields are lower than high-NO_x yields published earlier by our group. However, when OH radicals are produced via dark ozonolysis the SOA mass yields are comparable at high and low NO_x. Because pinonaldehyde is a major first-generation gas-phase product of α-pinene oxidation by either ozone or OH radicals, its potential to form SOA serves as a molecular counterpoint to bulk SOA aging experiments involving SOA formed from α-pinene. Both the general tendency for aging reactions to produce more SOA and the sensitivity of the low-NO_x products to UV photolysis observed in the bulk clearly occur for this single species as well. Photochemical oxidation of pinonaldehye and analogous first-generation terpene oxidation products are potentially a significant source of additional SOA in biogenically influenced air masses.