Atmospheric Chemistry and Physics Discussions
www.atmos-chem-phys-discuss.net
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8
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2008
10.5194/acpd-8-13619-2008
http://www.atmos-chem-phys-discuss.net/8/13619/2008/
http://www.atmos-chem-phys-discuss.net/8/13619/2008/acpd-8-13619-2008.html
http://www.atmos-chem-phys-discuss.net/8/13619/2008/acpd-8-13619-2008.pdf
13619
13632
2008-07-16
Emission of sunscreen salicylic esters from desert vegetation and their contribution to aerosol formation
S. N. Matsunaga
sou@atmchem.apchem.metro-u.ac.jp
A. B. Guenther
M. J. Potosnak
E. C. Apel
Advanced Study Program, National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder CO 80301, USA
Atmospheric Chemistry Division, National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder CO 80301, USA
Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA
Biogenic volatile organic compounds (BVOC) produced by plants are known to
have an important role in atmospheric chemistry. However, our knowledge of
the range of BVOCs produced by different plant processes is still expanding,
and there remain poorly understood categories of BVOCs. In this study,
emissions of a novel class of BVOC emissions were investigated in a desert
region. Our study considered 8 species of common desert plants: blackbrush
(<i>Coleogyne ramosissima</i>), desert willow (<i>Chilopsis linearis</i>), mesquite (<i>Prosopis glandulosa</i>),
mondel pine (<i>Pinus eldarica</i>), pinyon pine (<i>Pinus monophylla</i>),
cottonwood (<i>Populus deltoides</i>), saguaro cactus (<i>Carnegiea gigantea</i>)
and yucca (<i>Yucca baccata</i>). The measurements focused on
BVOCs with relatively high molecular weight (>C<sub>15</sub>) and/or an
oxygenated functional group. Significantly high emission rates of two
salicylic esters were found for blackbrush, desert willow and mesquite with
emission rates of 1.4, 2.1 and 0.46 μgC dwg<sup>−1</sup> h<sup>−1</sup>,
respectively. The salicylic esters were identified as 2-ethylhexenyl
salicylate (2-EHS) and 3,3,5-trimethylcyclohexenyl salicylate (homosalate)
and are known as effective ultraviolet (UV) absorbers. We propose that the
plants derive a protective benefit against UV radiation from the salicylic
esters and that the emission process is driven by the physical evaporation
of the salicylic esters due to the high ambient temperatures. In addition,
the salicylic esters are predicted to be an effective precursor of secondary
organic aerosol (SOA) because of their low vapor pressure due to a high
number of carbon atoms (15 or 16) and the presence of three oxygen atoms. We
estimated the contribution of the sunscreen esters themselves and their
oxidation products on the SOA formation for the Las Vegas region using a
BVOC emission model. The contribution was estimated to reach 90% of the
biogenic SOA in the landscapes dominated by desert willow and mesquite and
25% in Las Vegas area.
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