 |
| Titel |
The impact of anthropogenic emissions on atmospheric sulfate production pathways, oxidants, and ice core Δ¹⁷O(SO₄²⁻) |
| VerfasserIn |
E. D. Sofen, B. Alexander, S. A. Kunasek |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 7 ; Nr. 11, no. 7 (2011-04-15), S.3565-3578 |
| Datensatznummer |
250009611
|
| Publikation (Nr.) |
 copernicus.org/acp-11-3565-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
| We use a global three-dimensional chemical transport model to quantify the
influence of anthropogenic emissions on atmospheric sulfate production
mechanisms and oxidant concentrations constrained by observations of the
oxygen isotopic composition
(Δ17O = &delta17O–0.52 × &delta18O) of sulfate
in Greenland and Antarctic ice cores and aerosols. The oxygen isotopic
composition of non-sea salt sulfate (Δ17O(SO42–)) is a
function of the relative importance of each oxidant (e.g. O3, OH,
H2O2, and O2) during sulfate formation, and can be used to quantify
sulfate production pathways. Due to its dependence on oxidant concentrations,
Δ17O(SO42–) has been suggested as a proxy for paleo-oxidant levels. However,
the oxygen isotopic composition of sulfate from both Greenland and Antarctic
ice cores shows a trend opposite to that expected from the known increase in
the concentration of tropospheric O3 since the preindustrial period. The
model simulates a significant increase in the fraction of sulfate formed via
oxidation by O2 catalyzed by transition metals in the present-day Northern
Hemisphere troposphere (from 11% to 22%), offset by decreases in the
fractions of sulfate formed by O3 and H2O2. There is little change,
globally, in the fraction of tropospheric sulfate produced by gas-phase
oxidation (from 23% to 27%). The model-calculated change in
Δ17O(SO42–) since preindustrial times (1850 CE) is consistent
with Arctic and Antarctic observations. The model simulates a 42% increase
in the concentration of global mean tropospheric O3, a 10% decrease in
OH, and a 58% increase in H2O2 between the preindustrial period and
present. Model results indicate that the observed decrease in the Arctic
Δ17O(SO42–) – in spite of increasing tropospheric O3
concentrations – can be explained by the combined effects of increased
sulfate formation by O2 catalyzed by anthropogenic transition metals and
increased cloud water acidity, rendering Δ17O(SO42–)
insensitive to changing oxidant concentrations in the Arctic on this
timescale. In Antarctica, the Δ17O(SO42–) is sensitive to
relative changes of oxidant concentrations because cloud pH and metal
emissions have not varied significantly in the Southern Hemisphere on this
timescale, although the response of Δ17O(SO42–) to the
modeled changes in oxidants is small. There is little net change in the
Δ17O(SO42–) in Antarctica, in spite of increased O3, which
can be explained by a compensatory effect from an even larger increase in
H2O2. In the model, decreased oxidation by OH (due to lower OH
concentrations) and O3 (due to higher H2O2 concentrations) results
in little net change in Δ17O(SO42–) due to offsetting effects
of Δ17O(OH) and Δ17O(O3). Additional model simulations
are conducted to explore the sensitivity of the oxygen isotopic composition
of sulfate to uncertainties in the preindustrial emissions of oxidant
precursors. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|