Evaluation of emissions and transport of CFCs using surface observations and their seasonal cycles and the GEOS CCM simulation with emissions‐based forcing
Evaluation of emissions and transport of CFCs using surface observations and their seasonal cycles and the GEOS CCM simulation with emissions‐based forcing
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使用地面观测及其季节循环以及基于排放强迫的 GEOS CCM 模拟来评估 CFC 的排放和迁移
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发表时间：
2008
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通讯作者：
J. Nielsen
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作者：
Q. Liang;R. Stolarski;A. Douglass;P. Newman;J. Nielsen
[1]我们大气中的臭氧消耗物质（ODS）水平取决于生产，排放和损失过程。然而，大气模型是由这些消耗臭氧层物质的特定混合比率而不是更基本的基于排放的强迫作用所决定的。为了更准确地反映气候变化对大气环流和消耗臭氧层物质的物理和化学作用，从而反映未来的臭氧恢复情况，有必要在大气环流模型中从目前高度受限的基于混合比的强迫转换为基于排放的强迫。作为这一模式过渡的第一步，我们已经进行了45年（1960-2005年）的三个主要的氯氟烃（CFC-11，-12，-113）的排放为基础的模拟使用GEOS耦合化学气候模式（CCM）。模拟的CFC浓度和它们的季节性周期进行比较AGAGE和NOAA-GMD观测，以评估排放和大气传输。模拟的CFC-12与观测结果吻合得很好，表明对排放和大气损失的估计很好。模拟的CFC-11和CFC-113显示出由于过高估计排放量而产生的高度偏差。使用标记的CFC示踪剂跟踪最近的地面排放和老化的空气质量分别从平流层向下输送，我们量化的平流层对流层交换（STE）和对流层输送的CFC的季节性周期在对流层下部的相对贡献。对流层低层CFC的季节性循环主要由1985-1994年期间对流层输送的近期排放量决定。1995-1999年是一个过渡期，在这一时期，新排放量和STE引起的变化变得同等重要。2000-2004年期间，大多数地面站点的CFC季节性循环主要由STE控制。由于STE的CFC的季节性周期显示冬末/早春最大和夏季/秋季最小。在个别站点的对流层传输组件的季节性是由污染地区的新鲜排放的季节性运输变化。
[1] Levels of ozone depleting substances (ODSs) in our atmosphere are determined by production, emission, and loss processes. However, atmospheric models are forced by the specified mixing ratios of these ODSs rather than the more fundamental emissions-based forcing. To more accurately represent the physics and chemistry of climate change on atmospheric circulation and ODSs, and therefore future ozone recovery, it is desirable to switch from the current highly constrained mixing-ratio-based forcing to emissions-based forcing in general circulation models (GCMs). As a first step of this model transition, we have conducted a 45-year (1960-2005) emissions-based simulation of the three primary chlorofluorocarbons (CFC-11, -12, -113) using the GEOS coupled chemistry-climate model (CCM). The simulated CFC concentrations and their seasonal cycles are compared with AGAGE and NOAA-GMD observations to evaluate emissions and atmospheric transport. The simulated CFC-12 agrees well with the observations, indicating a good estimate of emission and atmospheric loss. The simulated CFC-11 and CFC-113 shows high biases due to overestimate of emissions. Using tagged CFC tracers to track recent surface emissions and aged air masses transported downward from the stratosphere separately, we quantify the relative contribution of stratosphere-troposphere exchange (STE) and tropospheric transport to the seasonal cycles of CFCs in the lower troposphere. The seasonal cycles of CFCs in the lower troposphere are dominated by tropospheric transport of recent emissions during 1985-1994. The 1995-1999 period marks the transition period when variations due to fresh emissions and STE become equally important. Seasonal cycles of CFCs at most surface sites in the 2000-2004 period are dominated by STE. Seasonal cycles of CFCs due to STE show a late winter/early spring maximum and a summer/fall minimum. Seasonality of the tropospheric transport component at individual stations is governed by seasonal transport variations of fresh emissions from the polluted regions.