Formation of new particles in the gas-phase ozonolysis of monoterpenes

The formation of organic acids and secondary organic aerosol in the gas-phase ozonolysis was investigated by laboratory experiments at 295±2 K in the absence of seed aerosol for a series of monoterpenes (β-pinene, sabinene, α-pinene, Δ3-carene, limonene, terpinolene) and methylene-cyclo-hexane and methyl-cyclo-hexene as model compounds. In the filter samples of the aerosol produced by ozonolysis series of organic acids were identified as methyl ester using GC/MS. In the ozonolysis of β-pinene, sabinene, α-pinene, Δ3-carene and limonene the corresponding C9-dicarboxylic acids were found as main products of the organic acid fraction. In case of terpinolene, methylene-cyclo-hexane and methyl-cyclo-hexene C7- and C6-dicarboxylic acids, respectively, were detected. The yields of these dicarboxylic acids were determined to range between 1 and 5 mol% using ion chromatography. Particle formation was observed with a 10 nm condensation nuclei counter after the consumption of (6.1±0.3)×1010 molecule cm−3 of β-pinene, sabinene, α-pinene, Δ3-carene and limonene, respectively. In case of terpinolene, methylene-cyclo-hexane and methyl-cyclo-hexene (1.8±0.1)×1011 molecule cm−3 of the reactants were converted. Upper limits for the partial vapor pressures of the dicarboxylic acids in the aerosol were determined to be (5.6±4.0)×10−8 Torr for the C9-dicarboxylic acids and (1.7±1.2)×10−7 Torr for the C7- and C6-dicarboxylic acids. The formation of secondary organic aerosol by ozonolysis of terpenes under suitable atmospheric conditions has most likely to be taken into account.