Variability and past long-term changes of brominated very short-lived substances at the tropical tropopause
Variability and past long-term changes of brominated very short-lived substances at the tropical tropopause
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DOI：
10.5194/acp-20-7103-2020
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发表时间：
2020-06
影响因子：
6.3
通讯作者：
S. Tegtmeier;E. Atlas;B. Quack;F. Ziska;K. Krüger
中科院分区：
文献类型：
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作者：
S. Tegtmeier;E. Atlas;B. Quack;F. Ziska;K. Krüger
抽象。溴仿（CHBr 3）等卤化极短寿命物质可被输送到平流层，导致卤素负荷和臭氧消耗。鉴于它们的排放率变化很大，而且在大气中的寿命很短，它们对平流层卤素含量的贡献的确切数量以及时空变化仍然不确定。我们将联合收割机观测数据集与拉格朗日大气模型相结合，以分析1979-2013年期间CHBr 3注入平流层的空间和时间变化。在17公里高度混合比高达0.4-0.5 ppt的区域最大值被诊断为在中美洲上空（1）和在海洋大陆-西太平洋上空（2），这两个都被高空飞机活动证实。在中美洲的CHBr 3最大值是由对流驱动的短传输时间尺度和强区域源的共同发生引起的，这两者共同驱动CHBr 3注入的季节性。在日常分辨率的模型结果显示，孤立的，异常高的CHBr 3值在该地区的ACCENT活动期间的飞机测量确认，并没有发生在空间或时间平均模型字段。西太平洋CHBr 3注入集中在赤道以南，由于强大的海洋源下面规定的自下而上的排放清单。全球最大的CHBr 3混合比在冷点水平高达0.6 ppt，被诊断为发生在印度，孟加拉湾和阿拉伯海地区（3）;然而，没有来自飞机活动的数据可以证实这一发现。平流层CHBr 3注入的年际变化率为10%-20%，这在很大程度上是由耦合的海洋-大气环流系统的变化率驱动的。另一方面，长期变化与区域海表温度趋势相关，导致西太平洋和亚洲季风区平流层CHBr 3注入的正趋势和东太平洋的负趋势。对于热带平均值，这些相反的区域趋势相互抵消，导致1979-2013年每十年0.017±0.012 ppt Br的相对较弱的正趋势，相当于每十年3% Br。CHBr 3和CH 2Br 2对平流层卤素负荷的总体贡献为4.7 ppt Br，与现有研究结果一致，其中50%和50%分别以源气体和产物气体的形式注入。
Abstract. Halogenated very short-lived substances (VSLSs), such as bromoform (CHBr3), can be transported to the stratosphere and contribute to the halogen loading and ozone depletion. Given their highly variable emission rates and their short atmospheric lifetimes, the exact amount as well as the spatio-temporal variability of their contribution to the stratospheric halogen loading are still uncertain. We combine observational data sets with Lagrangian atmospheric modelling in order to analyse the spatial and temporal variability of the CHBr3 injection into the stratosphere for the time period 1979–2013. Regional maxima with mixing ratios of up to 0.4–0.5 ppt at 17 km altitude are diagnosed to be over Central America (1) and over the Maritime Continent–west Pacific (2), both of which are confirmed by high-altitude aircraft campaigns. The CHBr3 maximum over Central America is caused by the co-occurrence of convectively driven short transport timescales and strong regional sources, which in conjunction drive the seasonality of CHBr3 injection. Model results at a daily resolution reveal isolated, exceptionally high CHBr3 values in this region which are confirmed by aircraft measurements during the ACCENT campaign and do not occur in spatially or temporally averaged model fields. CHBr3 injection over the west Pacific is centred south of the Equator due to strong oceanic sources underneath prescribed by the here-applied bottom-up emission inventory. The globally largest CHBr3 mixing ratios at the cold point level of up to 0.6 ppt are diagnosed to occur over the region of India, Bay of Bengal, and Arabian Sea (3); however, no data from aircraft campaigns are available to confirm this finding. Inter-annual variability of stratospheric CHBr3 injection of 10 %–20 % is to a large part driven by the variability of coupled ocean–atmosphere circulation systems. Long-term changes, on the other hand, correlate with the regional sea surface temperature trends resulting in positive trends of stratospheric CHBr3 injection over the west Pacific and Asian monsoon region and negative trends over the east Pacific. For the tropical mean, these opposite regional trends balance each other out, resulting in a relatively weak positive trend of 0.017±0.012 ppt Br per decade for 1979–2013, corresponding to 3 % Br per decade. The overall contribution of CHBr3 together with CH2Br2 to the stratospheric halogen loading accounts for 4.7 ppt Br, in good agreement with existing studies, with 50 % and 50 % being injected in the form of source and product gases, respectively.