 |
| Titel |
Infrared spectroscopic studies of the heterogeneous reaction of ozone with maleic and fumaric acid aerosols |
| VerfasserIn |
J. Najera, C. Percival, A. B. Horn |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250031245
|
|
|
|
|
|
| Zusammenfassung |
| Dicarboxylic acids, either directly emitted or formed in chemical processes are found to be a
significant component of tropospheric aerosols. To assess any potential role of short
unsaturated dicarboxylic acids in tropospheric heterogeneous chemistry, maleic acid (MaH)
and fumaric acid (FuH) were selected as surrogates in this study. A new aerosol flow tube
apparatus is employed to perform kinetic studies of the oxidation of organic compounds
containing aerosols by gas phase ozone. The system consists of a lab-made particle
generation system, a vertically oriented glass flow tube with moveable injector
and a multi-pass cross beam White cell for measurement of aerosol and gas phase
composition via Fourier transform infrared (FTIR) spectroscopy. A flow of single
component organic aerosols with mean diameters ranging between 0.8-2.1 μm are
introduced in a flow tube, in which the particles are subsequently exposed to a known
concentration of ozone for a controlled period of time. These studies are complemented
with offline analysis on the reaction products. Data from these studies were used to
determine the kinetics of the reaction under a range of conditions. The reaction
exhibited pseudo first order kinetics for gas product formation, and the pseudo
first order rate coefficients displayed a Langmuir-Hinshelwood dependence on gas
phase ozone concentration for both materials. By assuming Langmuir-Hinshelwood
behaviour, the following parameters were found: for the reaction of MaH aerosols,
KO3=(1.9+0.4)x10-16cm-3 and kmaxI=0.015+0.002; for the reaction of FuH aerosols,
KO3= (3.4+0.4)x10-16cm-3 and kmaxI=0.0128+0.0005, where KO3 is a parameter that
describes the partitioning of ozone to the particle surface and kmaxI is the maximum
pseudo-first order coefficient at high ozone concentrations. Apparent reactive uptake
coefficients were extracted from the pseudo first order rate coefficient and a slight trend of
decreasing uptake coefficients with increasing ozone concentrations was observed. In
general, we find that the values obtained for maleic and fumaric acid fall within the
range of literature values reported by other published studies for other organic or
organic-coated particles, although there are some unusual dependencies on RH%. |
|
|
|
|
|
|