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

The formation of organic acids and secondary organic aerosol in the gas-pha se ozonolysis was investigated by laboratory experiments at 295 +/- 2 K in the absence of seed aerosol for a series of monoterpenes (beta-pinene, sabi nene, alpha-pinene, Delta(3)-carene, limonene, terpinolene) and methylene-c yclo-hexane and methyl-cyclo-hexene as model compounds. In the filter sampl es of the aerosol produced by ozonolysis series of organic acids were ident ified as methyl ester using GC/MS. In the ozonolysis of beta-pinene, sabine ne, alpha-pinene, Delta(3)-carene and limonene the corresponding C-9-dicarb oxylic acids were found as main products of the organic acid fraction. In c ase of terpinolene, methylene-cyclo-hexane and methyl-cyclo-hexene C-7- and C-6-dicarboxylic acids, respectively, were detected. The yields of these d icarboxylic acids were determined to range between 1 and 5 mol% using ion c hromatography. Particle formation was observed with a 10 nm condensation nu clei counter after the consumption of (6.1 +/- 0.3) x 10(10) molecule cm(-3 ) of beta-pinene, sabinene, alpha-pinene, Delta(3)-carene and limonene, res pectively. In case of terpinolene, methylene-cyclo-hexane and methyl-cyclo- hexene (1.8 +/- 0.1) x 10(11) molecule cm(-3) of the reactants were convert ed. Upper limits for the partial vapor pressures of the dicarboxylic acids in the aerosol were determined to be (5.6 +/- 4.0)x 10(-8) Torr for the Cg- dicarboxylic acids and (1.7 +/- 1.2)x 10(-7) Torr for the C7- and C-6-dicar boxylic acids. The formation of secondary organic aerosol by ozonolysis of terpenes under suitable atmospheric conditions has most likely to be taken into account. (C) 2000 Published by Elsevier Science Ltd.