Web Release Date: April 27,
Contributions of Organic Peroxides to Secondary Aerosol Formed from Reactions of Monoterpenes with O3
and
Air Pollution Research Center, University of California, Riverside, California 92521
Received for review February 2, 2005
Revised manuscript received March 18, 2005
Accepted March 18, 2005
Abstract:
The role of organic peroxides in secondary organic
aerosol (SOA) formation from reactions of monoterpenes
with O3 was investigated in a series of environmental chamber
experiments. Reactions were performed with endocyclic
(
-pinene and 
3-carene) and exocyclic (
-pinene and
sabinene) alkenes in dry and humid air and in the presence
of the OH radical scavengers: cyclohexane, 1-propanol,
and formaldehyde. A thermal desorption particle beam mass
spectrometer was used to probe the identity and volatility
of SOA components, and an iodometric-spectrophotometric method was used to quantify organic peroxides.
Thermal desorption profiles and mass spectra showed that
the most volatile SOA components had vapor pressures
similar to pinic acid and that much of the SOA consisted
of less volatile species that were probably oligomeric
compounds. Peroxide analyses indicated that the SOA was
predominantly organic peroxides, providing evidence
that the oligomers were mostly peroxyhemiacetals formed
by heterogeneous reactions of hydroperoxides and
aldehydes. For example, it was estimated that organic
peroxides contributed ~47 and ~85% of the SOA mass
formed in the - and -pinene reactions, respectively.
Reactions performed with different OH radical scavengers
indicated that most of the hydroperoxides were formed
through the hydroperoxide channel rather than by reactions
of stabilized Criegee intermediates. The effect of the OH
radical scavenger on the SOA yield was also investigated,
and the results were consistent with results of recent
experiments and model simulations that support a mechanism
based on changes in the [HO2]/[RO2] ratios. These are
the first measurements of organic peroxides in monoterpene
SOA, and the results have important implications for
understanding the mechanisms of SOA formation and the
potential effects of atmospheric aerosol particles on
the environment and human health.
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