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| Titel |
Ozone adsorption on carbon nanoparticles |
| VerfasserIn |
Guillaume Chassard, Sylvie Gosselin, Nicolas Visez, Denis Petitprez |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096552
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| Publikation (Nr.) |
 EGU/EGU2014-12061.pdf |
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| Zusammenfassung |
| Carbonaceous particles produced by incomplete combustion or thermal decomposition of
hydrocarbons are ubiquitous in the atmosphere. On these particles are adsorbed hundreds of
chemical species. Those of great concern to health are polycyclic aromatic hydrocarbons
(PAHs). During atmospheric transport, particulate PAHs react with gaseous oxidants. The
induced chemical transformations may change toxicity and hygroscopicity of these
potentially inhalable particles. The interaction between ozone and carbon particles has
been extensively investigated in literature. However ozone adsorption and surface
reaction mechanisms are still ambiguous. Some studies described a fast catalytic
decomposition of ozone initiated by an atomic oxygen chemisorption followed by a
molecular oxygen release [1-3]. Others suggested a reversible ozone adsorption
according to Langmuir-type behaviour [4,5]. The aim of this present study is a better
understanding of ozone interaction with carbon surfaces. An aerosol of carbon
nanoparticles was generated by flowing synthetic air in a glass tube containing pure carbon
(primary particles < 50 nm), under magnetic stirring. The aerosol was then mixed with
ozone in an aerosol flow tube. Ozone uptake experiments were performed with
different particles concentrations with a fixed ozone concentration. The influence of
several factors on kinetics was examined: initial ozone concentration, particle size
(50 nm -¤ Dp -¤ 200 nm) and competitive adsorption (with probe molecule and
water).
The effect of initial ozone concentration was first studied. Accordingly to literature, it has
been observed that the number of gas-phase ozone molecules lost per unit particle surface
area tends towards a plateau for high ozone concentration suggesting a reversible
ozone adsorption according to a Langmuir mechanism. We calculated the initial
reaction probability between O3 and carbon particles.An initial uptake coefficient of
1.10-4 was obtained. Similar experiments were realized by selecting the particles
size with a differential mobility analyser. We observed a strong size-dependent
increase in reactivity with the decrease of particles size. This result is relevant for the
health issues. Indeed the smallest particles are most likely to penetrate deep into the
lungs.
Competitive reactions between ozone and other species like H2O or atomic oxygen were
also considered. Oxygen atoms were generated by photolysis of O3 (or O2) and were chosen
because it is believed to form the same reactive oxygen intermediates than ozone. A weak
water physisorption on soot was observed revealing hydrophobic properties of particles.
Oxygen atoms were found to be strongly reactive. A Langmuir behavior was observed for
oxygen atoms adsorption on carbon particles and we were able to determine an initial uptake
coefficient of approximately 2.10-2.
[1] Fenidel, W., et al., Interaction between carbon or iron aerosol particles and ozone.
Atmospheric Environment, 1995. 29(9): p. 967-973.
[2] Smith, D. and A. Chughtai, Reaction kinetics of ozone at low concentrations with
n-hexane soot. Journal of geophysical research, 1996. 101(D14): p. 19607-19,620.
[3] Kamm, S., et al., The heterogeneous reaction of ozone with soot aerosol. Atmospheric
Environment, 1999. 33(28): p. 4651-4661.
[4] Stephens, S., M.J. Rossi, and D.M. Golden, The heterogeneous reaction of ozone on
carbonaceous surfaces. International journal of chemical kinetics, 1986. 18(10): p.
1133-1149.
[5] Pöschl, U., et al., Interaction of ozone and water vapor with spark discharge soot
aerosol particles coated with benzo [a] pyrene: O3 and H2O adsorption, benzo [a] pyrene
degradation, and atmospheric implications. The Journal of Physical Chemistry A, 2001.
105(16): p. 4029-4041. |
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