Gas-Phase Ozone Oxidation of Monoterpenes: Gaseous and ...

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Table IX. Gaseous and particulate product yields in the β-pinene/O 3 reaction Molar yield (%) Aerosol yield by mass Gas Aerosol Total (%) Experiment data 6/11/98b 6/17/98b 6/11/98b 6/17/98b 6/11/98b 6/17/98b 6/11/98b 6/17/98b Pinic acid 1.7 2.5 0.91 1.2 2.6 3.7 1.2 1.6 Norpinic acid 0.23 0.17 0.11 0.09 0.35 0.27 0.17 0.12 Pinonic acid 0.41 0.56 0.10 0.19 0.52 0.74 0.14 0.25 Norpinonic acid and isomer 4.6 14.3 1.3 2.2 5.9 16.5 1.7 2.7 Hydroxy pine ketones 6.6 7.9 0.66 1.1 7.3 9.0 0.74 1.3 3-Oxo-pina-ketone 1.8 7.6 0.02 0.11 1.8 7.7 0.02 0.12 2,2-Dimethyl-cyclobutane- 0.35 0.29 ND a ND 0.35 0.29 ND ND 1,3-dicarboxaldehyde Nopinone 17.0 15.8 trace trace 17.0 15.8 trace trace Hydroxy norpinonic acid 0.58 0.98 0.10 0.24 0.68 1.2 0.14 0.33 Hydroxy pinonic acid 0.26 0.16 0.17 0.15 0.43 0.31 0.25 0.20 Total molar yield 33.5 50.3 3.4 5.3 36.9 55.6 4.4 6.6 Carbon-based total yield 34.2 50.1 Aerosol yield measured by SEMS and CNC 4.5 8.3 a Not detectable. 238 JIANZHEN YU ET AL.
GAS-PHASE OZONE OXIDATION OF MONOTERPENES 239 pinene (275 to 440 ppmv) and ozone (179 to 270 ppmv), and no OH scavenger. The very different reaction conditions may account for the different product yields. The identified products account for 34% and 50% of the reacted β-pinene carbon mass in the 6/11/98b and 6/17/98b experiments, respectively. Products with a yield exceeding >1% include nopinone (15.8–17.0%), hydroxy pina ketones (7.3–9.0%), 3-oxo-pina-ketone (1.8–7.7%), norpinonic acid and its isomers (5.9– 16.5%), and pinic acid (2.6–3.7%). The identified products are estimated to account for 98% and 83% of the organic aerosol mass formed in the two β-pinene/O 3 experiments. Norpinonic acid and its isomers, pinic acid and hydroxy pina ketones are SOA components that contribute to more than 10% of the organic aerosol mass. The 6/17/98b experiment has a much higher percentage of reacted β-pinene accounted for by the identified products than the 6/11/98b experiment, as two major products, norpinonic acid and its isomers and 3-oxo-pina-ketone, were observed to have much higher gas-phase yields in the 6/17/98b experiment (Table IX). The two β-pinene/O 3 experiments were conducted under different initial conditions, i.e., ozone was present in an excess amount in the 6/11/98b experiment whereas β-pinene is in excess in the 6/17/98b experiment (Table I). The variation between the two experiments can not be accounted for by measurement error alone. It is possible the different initial reaction conditions are responsible for the variation, but a satisfactory explanation is not possible without further experiments designed to systematically examine the effects of different reaction conditions on product yields. The functional group distribution of SOA components from the β-pinene/O 3 experiments is comparable to results obtained by Palen et al. (1992) using Fourier transform infrared spectrometry (FTIR). Palen et al. analyzed aerosol samples generated from an experiment with 8 ppmv O 3 and 14.5 ppmv β-pinene. Their results indicated that an average aerosol-phase product molecule contained one ketone group, 0.7 alcohol groups, and 0.4 carboxylic groups. For the 6/17/98 β-pinene/O 3 experiment where excessive β-pinene was used, our GC/MS analysis showed that the average aerosol molecule contained about one ketone group, 0.2 alcohol groups, and 0.8 carboxylic groups. 4.2. SABINENE Table X shows yields of individual products in the gas and aerosol phases, as well as the total yields of both phases in the sabinene/O 3 experiment. Identified products in both the gas and aerosol phases account for 57% of the reacted sabinene carbon mass. Products with a molar yield exceeding 1% include sabina ketone (47%), hydroxy sabina ketone (7%), norsabinonic acid and its isomers (5%), pinic acid (1%), and sabinic acid (1%). All the products added together account for 100% of the organic aerosol mass formed. The 100% yield is rather fortuitous, and it is associated with an uncertainty factor resulting from the approximations made for response factors and SOA
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