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| Titel |
Photosensitised heterogeneous oxidation kinetics of biomass burning aerosol surrogates by ozone using an irradiated rectangular channel flow reactor |
| VerfasserIn |
S. M. Forrester, D. A. Knopf |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 13, no. 13 ; Nr. 13, no. 13 (2013-07-09), S.6507-6522 |
| Datensatznummer |
250018749
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| Publikation (Nr.) |
 copernicus.org/acp-13-6507-2013.pdf |
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| Zusammenfassung |
| Heterogeneous reaction kinetics involving organic aerosol and atmospheric
oxidants such as ozone can be enhanced under visible or UV irradiation in the
presence of a photosensitiser, with subsequent implications for the climate,
cloud radiative properties, air quality, and source appointment. In this
study we report the steady-state reactive uptake coefficient, γ, of
O3 by levoglucosan and 5-nitroguaiacol acting as surrogates for biomass
burning aerosol particles, with and without the presence of Pahokee peat
acting as a photosensitiser. The reactive uptake has been determined in the
dark and as a function of visible and UV-A irradiation and ozone
concentration. In addition, γ was determined for 1 : 1, 1 : 10,
and 1 : 100 by mass mixtures of Pahokee peat and 5-nitroguaiacol, and for a
10 : 1 : 3 mixture of levoglucosan, Pahokee peat, and 5-nitroguaiacol. We
developed a novel irradiated rectangular channel flow reactor (I-RCFR) that
was operated under low pressures of about 2–4 hPa, and allowed for uniform
irradiation of the organic substrates. The I-RCFR was coupled to a chemical
ionisation mass spectrometer and has been successfully validated by measuring
the kinetics between various organic species and oxidants. γ of O3
and levoglucosan in the dark and under visible and UV-A irradiation was
determined to be in the range of (2–11) × 10−6 and did not
change in the presence of Pahokee peat. The determined γ of O3 and
5-nitroguaiacol in the dark was 5.7 × 10−6 and was only
enhanced under UV-A irradiation, yielding a value of
3.6 × 10−5. γ of the 1 : 1 Pahokee peat/5-nitroguaiacol
substrate was enhanced under visible and UV-A irradiation to 2.4 ×
10−5 and 2.8 × 10−5, respectively. Decreasing the amount of
Pahokee peat in the 5-nitroguaiacol/Pahokee peat substrate resulted in lower
values of γ under visible irradiation, however, γ was
consistent under UV-A irradiation regardless of the amount of Pahokee peat.
The 10 : 1 : 3 mixture by mass of levoglucosan, Pahokee peat, and
5-nitroguaiacol, under both visible and UV-A irradiation yielded γ
values of 2.8 × 10−5 and 1.4 × 10−5,
respectively. γ was determined as a function of photon flux for O3
with the 1 : 1 Pahokee peat/5-nitroguaiacol substrate, yielding a linear
relationship under both visible and UV-A irradiation. γ of O3 with
the 1 : 1 Pahokee peat/5-nitroguaiacol substrate was determined as a function
of ozone concentration and exhibited an inverse dependence of γ on
ozone concentration, commonly interpreted as a Langmuir–Hinshelwood
mechanism. The reactive uptake data have been represented by a Langmuir-type
isotherm. From the O3 uptake data under visible irradiation, the following
fit parameters have been derived: ks = (5.5 ± 2.7) × 10−19 cm2 s−1 molecule−1 and
KO3 = (2.3 ± 2.0) × 10−12 cm3 molecule−1; and under UV-A irradiation:
ks = (8.1 ± 2.0) × 10−19 cm2 s−1 molecule−1 and KO3 =
(1.7 ± 0.7) × 10−12 cm3 molecule−1. The oxidative power, or the
product of γ and [O3], was determined for O3 with the 1 : 1
Pahokee peat/5-nitroguaiacol substrate and was in the range of
(1.2–26) × 106 molecule cm−3. Atmospheric particle
lifetimes were estimated for a 0.4 μm 5-nitroguaiacol particle as a
function of visible and UV-A irradiation and ozone concentration. |
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