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| Titel |
A comparison of radical and non-radical conversion rates of SVOCs in the tropospheric condensed phase |
| VerfasserIn |
Andreas Tilgner, Hartmut Herrmann |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039261
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| Zusammenfassung |
| Secondary formation pathways of organic compounds are currently intensely discussed
including conversions in tropospheric aqueous particles as well as cloud droplets.
Particularly, SVOCs (Semivolatile Organic Compounds) and their reaction products are
expected to be potential precursors for the formation of higher molecular organic compounds.
In the aqueous phase, such compounds can undergo both various oxidative processes (radical
and non-radical oxidants reactions) and non oxidative processes (aldol, acetal, dimerisation
and ester formation reactions). These chemical aqueous phase processes are expected to be
very efficient proceeding on short timescales and produce multifunctional organic compounds
of less volatility. However, the importance of non-radical reactions compared to currently
known radical oxidations under different conditions has not yet been assessed .Current
aqueous phase mechanisms such as CAPRAM (Chemical Aqueous Phase RAdical
Mechanism; Herrmann et al., 2005) do consider radical oxidation processes of organic
compounds.
In the present study, a comparison of radical and non-radical conversion rates of
organics in cloud droplet and aqueous particles is performed for both urban and remote
environmental conditions. For the comparison, available reaction rate constants
have been used together with outcome of recent model simulations (Tilgner and
Herrmann, 2010) using the CAPRAM 3.0i mechanism. First order-conversion rate
constants in the aqueous phase for cloud and aqueous particle conditions, for (i) OH,
(ii) NO3, (iii) H2O2, (iv) the aldol condensation, (v) the dimerisation and (vi) the
ammonium-catalysed accretion reactions were calculated with the available, at
current quite restricted data set. From the comparison, it is concluded that organic
accretion reactions might be of interest in some cases but generally do by far not reach
the oxidative conversion rates of radical and non-radical oxidants. Particularly,
the adol condensation reactions can sometimes be partly competitive with radical
oxidation reactions and might, to some extend, act as a non-oxidative pathway for less
volatile organics with aldehyde functionalities. Additionally, reactions of H2O2
with easily oxidisable SVOCs such as glyoxal and pyruvic acid are shown to be
competitive to the OH radical conversions when H2O2 is not being strongly depleted by
sulphur(IV).
References:
Herrmann, H.; Tilgner, A.; Barzaghi, P.; Majdik, Z.; Gligorovski, S.; Poulain, L.; Monod,
A. Towards a more detailed description of tropospheric aqueous phase organic chemistry:
CAPRAM3.0. Atmos. Environ. 2005, 39, 4351–4363.
Tilgner, A.; Herrmann, H. Radical-driven carbonyl-to-acid conversion and acid
degradation in tropospheric aqueous systems studied by CAPRAM. Atmos. Environ. 2010,
submitted for publication. |
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