The impact of anthropogenic emissions on atmospheric sulfate production pathways, oxidants, and ice core Δ 17 O(SO 4 2– )

• Published in: Atmospheric Chemistry and Physics
• Main Authors: S. A. Kunasek, B. Alexander, E. D. Sofen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2011
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Arctic; Antarctic; Greenland; Antarc*; ice core
• Online Access: https://doi.org/10.5194/acp-11-3565-2011; https://doaj.org/article/afda79d225c0497697e19c1c1813110e

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 (Δ 17 O = &delta 17 O–0.52 × &delta 18 O) of sulfate in Greenland and Antarctic ice cores and aerosols. The oxygen isotopic composition of non-sea salt sulfate (Δ 17 O(SO 4 2– )) is a function of the relative importance of each oxidant (e.g. O 3 , OH, H 2 O 2 , and O 2 ) during sulfate formation, and can be used to quantify sulfate production pathways. Due to its dependence on oxidant concentrations, Δ 17 O(SO 4 2– ) 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 O 3 since the preindustrial period. The model simulates a significant increase in the fraction of sulfate formed via oxidation by O 2 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 O 3 and H 2 O 2 . 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 Δ 17 O(SO 4 2– ) 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 O 3 , a 10% decrease in OH, and a 58% increase in H 2 O 2 between the preindustrial period and present. Model results indicate that the observed decrease in the Arctic Δ 17 O(SO 4 2– ) – in spite of increasing tropospheric O 3 concentrations – can be explained by the combined effects of increased sulfate formation by O 2 catalyzed by anthropogenic transition metals and increased cloud water acidity, rendering Δ 17 O(SO 4 2– ) insensitive to changing ...