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

GAS-PHASE OZONE OXIDATION OF MONOTERPENES 255
Figure 17. Reaction mechanism of O 3 / 3 -carene reaction.
In addition to expected products, a number of products having minor yields that
are unique to each monoterpene have also been detected. One interesting finding
that is yet to be explained is the presence of pinic acid in both the sabinene/O 3 and
3 -carene/O 3 reactions.
Yields of individual products in both the gas and aerosol phases have been
determined or estimated, thus providing a direct measure of the gas-particle partitioning
of each product. The identified products account for a significant fraction
of the secondary organic aerosol for each of the parent hydrocarbons. Identified
products, in both gas and aerosol phases, are estimated to account for about 34–
50%, 57%, 29–67%, and 24% of the total reacted carbon mass for β-pinene,
sabinene, α-pinene, and 3 -carene, respectively. Whereas these percentages exceed
those of previous studies, a significant fraction of the monoterpenes reacted
still remains unaccounted for. As the yields of many products are estimated using
the response factor of surrogates, an improved mass balance awaits authentic standards
or new analytical techniques that do not require authentic standards. Based on
experimentally measured gas-particle partitioning coefficients of individual oxidation
products, it is possible to evaluate the extent to which overall aerosol yields
observed in smog chamber experiments can be represented by the stoichiometric
yields and gas-particle partitioning of the individual products.
Based on the nature and yield of various aerosol components, products such
as pinic acid, pinonic acid, norpinonic acid, hydroxy pinonic acid, and hydroxy