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| Titel |
Quantification of chemical and physical processes influencing ozone during long-range transport using a trajectory ensemble |
| VerfasserIn |
M. Cain, J. Methven, E. J. Highwood |
| 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 ; 12, no. 15 ; Nr. 12, no. 15 (2012-08-03), S.7015-7039 |
| Datensatznummer |
250011368
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| Publikation (Nr.) |
 copernicus.org/acp-12-7015-2012.pdf |
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| Zusammenfassung |
During long-range transport, many distinct processes – including
photochemistry, deposition, emissions and mixing – contribute to the
transformation of air mass composition. Partitioning the effects of different
processes can be useful when considering the sensitivity of chemical
transformation to, for example, a changing environment or anthropogenic
influence. However, transformation is not observed directly, since mixing
ratios are measured, and models must be used to relate changes to processes.
Here, four cases from the ITCT-Lagrangian 2004 experiment are studied. In
each case, aircraft intercepted a distinct air mass several times during
transport over the North Atlantic, providing a unique dataset and quantifying
the net changes in composition from all processes. A new framework is
presented to deconstruct the change in O3 mixing ratio (Δ O3)
into its component processes, which were not measured directly, taking
into account the uncertainty in measurements, initial air mass variability
and its time evolution.
The results show that the net chemical processing (Δ O3chem)
over the whole simulation is greater than net physical
processing (Δ O3phys) in all cases. This is in part
explained by cancellation effects associated with mixing. In contrast, each
case is in a regime of either net photochemical destruction (lower
tropospheric transport) or production (an upper tropospheric biomass burning
case). However, physical processes influence O3 indirectly through
addition or removal of precursor gases, so that changes to physical
parameters in a model can have a larger effect on Δ O3chem
than Δ O3phys. Despite its smaller magnitude, the physical
processing distinguishes the lower tropospheric export cases, since the net
photochemical O3 change is −5 ppbv per day in all three cases.
Processing is quantified using a Lagrangian photochemical model with a novel
method for simulating mixing through an ensemble of trajectories and a
background profile that evolves with them. The model is able to simulate the
magnitude and variability of the observations (of O3, CO,
NOy and some hydrocarbons) and is consistent with the
time-average OH following air-masses inferred from hydrocarbon measurements
alone (by Arnold et al., 2007). Therefore, it is a useful new method to
simulate air mass evolution and variability, and its sensitivity to process
parameters. |
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