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 (17O = &delta17O–0.52 × &delta18O) of sulfate in Greenland and Antarctic ice cores and aerosols. The oxygen isotopic composition of non-sea salt sulfate (17O(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, 17O(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 17O(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 17O(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 17O(SO42) insensitive to changing oxidant concentrations in the Arctic on this timescale. In Antarctica, the 17O(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 17O(SO42) to the modeled changes in oxidants is small. There is little net change in the 17O(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 17O(SO42) due to offsetting effects of 17O(OH) and 17O(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.
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机译：我们使用全球三维化学传输模型来量化人为排放对大气硫酸盐生产机制的影响，并通过观察格陵兰和南极冰核的硫酸盐的氧同位素组合物（17O =＆Delta17O-0.52×＆Delta18o）的观察限制和气溶胶。非海盐硫酸盐（17O（SO 42））的氧同位素组合物是硫酸盐形成期间每种氧化剂（例如O 3，OH，H 2 O 2和O 2）的相对重要性的函数，并且可用于量化硫酸盐生产途径。由于其对氧化剂浓度的依赖性，已经提出了17O（SO 42）作为古氧化剂水平的代理。然而，来自格陵兰和南极冰芯的硫酸盐的氧同位素组成显示出与预工业时期的对流层O3浓度的已知增加的预期相反的趋势。该模型模拟了通过在本日北半球对流层上过渡金属催化的O2形成的硫酸酯的级数显着增加（从11％〜22％），通过O 3和H 2 O 2形成的硫酸酯的级分偏移。全球变化几乎没有变化，在通过气相氧化（23％至27％）产生的对流层硫酸盐的级分。自预工业次数（1850 CE）以来，17O（SO42）的模型计算变化与北极和南极观察一致。该模型模拟了全局平均对流层O3的浓度增加了42％，oh的10％降低，在预生产期与现在的H2O2增加了58％。模型结果表明，虽然催化硫酸盐形成增加的硫酸盐形成和增加的云水酸度，但仍然可以通过增加硫酸盐形成和增加的云水酸度，所观察到的北极17O（SO42） - 尽管增加了硫酸盐形成的综合影响，并提高了云水酸度，呈现17O（ SO42）对在这种时间尺度上改变北极氧化浓度的不敏感。在南极洲，17O（SO42）对氧化剂浓度的相对变化敏感，因为在这种时间尺度的南半球在南半球上没有显着变化，尽管17O（SO42）对氧化剂的建模变化的反应很小。南极洲的17O（SO42）仍然很少有净变化，尽管O3增加，可以通过从H2O2的甚至更大增加的补偿效果来解释。在该模型中，通过OH（由于较低的OH浓度）和O 3（由于较高的H 2 O 2浓度）降低氧化，导致17O（SO42）的净变化很少（SO 42），这是17O（OH）和17O（O 3）的偏移作用。进行了额外的模型模拟，以探讨硫酸盐对氧化剂前体的前工业排放中的不确定性的氧同位素组合物的敏感性。
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