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

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