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| Titel |
A model study of the impact of source gas changes on the stratosphere for 1850–2100 |
| VerfasserIn |
E. L. Fleming, C. H. Jackman, R. S. Stolarski, A. R. Douglass |
| 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 ; 11, no. 16 ; Nr. 11, no. 16 (2011-08-22), S.8515-8541 |
| Datensatznummer |
250010019
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| Publikation (Nr.) |
 copernicus.org/acp-11-8515-2011.pdf |
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| Zusammenfassung |
The long-term stratospheric impacts due to emissions of
CO2, CH4, N2O, and ozone depleting
substances (ODSs) are investigated using an updated version of
the Goddard two-dimensional (2-D) model. Perturbation
simulations with the ODSs, CO2, CH4, and
N2O varied individually are performed to isolate the
relative roles of these gases in driving stratospheric changes
over the 1850–2100 time period. We also show comparisons with
observations and the Goddard Earth Observing System
chemistry-climate model simulations for the time period
1960–2100 to illustrate that the 2-D model captures the basic
processes responsible for long-term stratospheric change.
The ODSs, CO2, CH4, and N2O impact ozone via
several mechanisms. ODS and N2O loading decrease
stratospheric ozone via the increases in atmospheric halogen and
odd nitrogen species, respectively. CO2 loading impacts
ozone by: (1) cooling the stratosphere which increases ozone via
the reduction in the ozone chemical loss rates, and (2) accelerating the Brewer-Dobson circulation (BDC) which
redistributes ozone in the lower stratosphere. The net result of
CO2 loading is an increase in global ozone in the total
column and upper stratosphere. CH4 loading impacts ozone
by: (1) increasing atmospheric H2O and the odd hydrogen
species which decreases ozone via the enhanced HOx-ozone loss
rates; (2) increasing the H2O cooling of the middle
atmosphere which reduces the ozone chemical loss rates,
partially offsetting the enhanced HOx-ozone loss; (3) converting
active to reservoir chlorine via the reaction
CH4+Cl→HCl+CH3 which leads to more ozone; and (4) increasing the NOx-ozone production in the
troposphere. The net result of CH4 loading is an ozone
decrease above 40–45 km, and an increase below 40–45 km and in
the total column.
The 2-D simulations indicate that prior to 1940, the ozone
increases due to CO2 and CH4 loading outpace
the ozone losses due to increasing N2O and carbon
tetrachloride (CCl4) emissions, so that total column and
upper stratospheric global ozone reach broad maxima during the
1920s–1930s. This precedes the
significant ozone depletion during ~1960–2050 driven by
the ODS loading. During the latter half of the 21st century as
ODS emissions diminish, CO2, N2O, and
CH4 loading will all have significant impacts on
global total ozone based on the Intergovernmental Panel on
Climate Change (IPCC) A1B (medium) scenario,
with CO2 having the largest individual
effect. Sensitivity tests illustrate that due to the strong
chemical interaction between methane and chlorine, the
CH4 impact on total ozone becomes significantly more
positive with larger ODS loading. The model simulations also
show that changes in stratospheric temperature, BDC, and age of
air during 1850–2100 are
controlled mainly by the CO2 and ODS loading. The
simulated acceleration of the BDC causes the global average age of air above 22 km to
decrease by ~1 yr from 1860–2100. The
photochemical lifetimes of N2O, CFCl3,
CF2Cl2, and CCl4 decrease by 11–13 %
during 1960–2100 due to the acceleration of the BDC, with
much smaller lifetime changes (<4 %) caused by changes in
the photochemical loss rates. |
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