Seasonal impact of biogenic very short-lived bromocarbons on lowermost stratospheric ozone between 60° N and 60° S during the 21st century
Seasonal impact of biogenic very short-lived bromocarbons on lowermost stratospheric ozone between 60° N and 60° S during the 21st century
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DOI：
10.5194/acp-20-8083-2020
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发表时间：
2020-07-13
影响因子：
6.3
通讯作者：
Saiz-Lopez, Alfonso
中科院分区：
文献类型：
--
作者：
Alejandro Barrera, Javier;Pedro Fernandez, Rafael;Saiz-Lopez, Alfonso
目前，生物源极短寿命溴碳（VSLBr）约占平流层溴总负载的25%。由于其寿命比人类活动产生的寿命较长的溴（如哈龙）和氯（如氯氟烃）短得多，VLBr对臭氧的影响在平流层最低层达到峰值，而平流层是一个关键的气候和辐射大气区域。在这里，我们提出了一个模拟研究的平流层臭氧的演变及其化学损失的热带地区和中纬度地区在21世纪世纪。两个不同的实验进行了探讨：考虑和忽略额外的平流层注入5 ppt的生物溴自然释放的海洋。我们的分析表明，列入VSLBr的结果在一个现实的平流层溴负载，并提高了1980-2015年期间在中纬度地区的总臭氧柱（TOC）的模型和卫星观测之间的协议。我们表明，中纬度地区臭氧对VSLBr的总体响应遵循整个21世纪平流层长寿无机氯和溴的演变。目前（1990-2010年），由于VSLBr造成的额外臭氧损失最大，南半球和北方半球中纬度地区（SH-ML和NH-ML）的TOC差异分别为-8 DU（-3%）和-5.5 DU（-2%）。此外，预计的TOC差异在21世纪末的世纪是类似的50%，低于发现的值为现今period.We发现，季节性的VSLBr在中纬度平流层最低臭氧的影响是由季节性的异质无机氯再活化过程的冰晶。事实上，由于更有效地重新激活的氯水库（主要是ClONO 2和HCl）在较冷的SH-ML最低平流层，季节性的VSLI Br的影响显示了一个小的，但持久的半球不对称通过整个建模期间。我们的研究结果表明，虽然整体VSLBr驱动的臭氧破坏是最大的春季，卤素介导的（HALGOs（x-损失））臭氧损失周期在中纬度最低的平流层在冬季是相对更有效的比HOx循环相对于其他季节。事实上，当考虑VSLBr时，在1985年至2020年期间，在SH-ML处，HNOs（x-损失）主导冬季最低平流层臭氧损失，卤素间ClOx-BrOx循环对HNOs（x-损失）的贡献接近50%。由VSLBr介导的小（<-2.5DU）和相对恒定（类似于-1%）的臭氧消耗与其在整个模拟期间的固定排放密切相关。通过纳入VSLBr来源，BrOx循环实际上主导了对最低平流层臭氧损失的季节性H2O（x-损失）贡献，反映了极短寿命（VSL）溴对驱动热带平流层臭氧消耗的背景卤素丰度的敏感性较低。我们的结论是，生物溴源和季节性变化的异质氯再活化之间的联系是未来预测中纬度最低平流层臭氧在21世纪的一个关键特征。
Biogenic very short-lived bromocarbons (VSLBr) currently represent similar to 25 % of the total stratospheric bromine loading. Owing to their much shorter lifetime compared to anthropogenic long-lived bromine (e.g. halons) and chlorine (e.g. chlorofluorocarbons), the impact of VSLBr on ozone peaks in the lowermost stratosphere, which is a key climatic and radiative atmospheric region. Here we present a modelling study of the evolution of stratospheric ozone and its chemical loss within the tropics and at mid-latitudes during the 21st century. Two different experiments are explored: considering and neglecting the additional stratospheric injection of 5 ppt biogenic bromine naturally released from the ocean. Our analysis shows that the inclusion of VSLBr results in a realistic stratospheric bromine loading and improves the agreement between the model and satellite observations of the total ozone column (TOC) for the 1980-2015 period at mid-latitudes. We show that the overall ozone response to VSLBr at mid-latitudes follows the stratospheric evolution of long-lived inorganic chlorine and bromine throughout the 21st century. Additional ozone loss due to VSLBr is maximized during the present-day period (1990-2010), with TOC differences of -8 DU (-3 %) and -5.5 DU (-2 %) for the Southern Hemisphere and Northern Hemisphere midlatitudes (SH-MLs and NH-MLs), respectively. Moreover, the projected TOC differences at the end of the 21st century are similar to 50 % lower than the values found for the present-day period.We find that seasonal VSLBr impact on lowermost stratospheric ozone at mid-latitude is influenced by the seasonality of the heterogeneous inorganic-chlorine reactivation processes on ice crystals. Indeed, due to the more efficient reactivation of chlorine reservoirs (mainly ClONO2 and HCl) within the colder SH-ML lowermost stratosphere, the seasonal VSLBr impact shows a small but persistent hemispheric asymmetry through the whole modelled period. Our results indicate that, although the overall VSLBr -driven ozone destruction is greatest during spring, the halogen-mediated (Halog(x-Loss)) ozone loss cycle in the mid-latitude lower-most stratosphere during winter is comparatively more efficient than the HOx cycle with respect to other seasons. Indeed, when VSLBr are considered, Halog(x-Loss) dominates wintertime lowermost stratospheric ozone loss at SH-MLs between 1985 and 2020, with a contribution of inter-halogen ClOx-BrOx cycles to Halog(x-Loss) of similar to 50 %.Within the tropics, a small (< -2.5 DU) and relatively constant (similar to -1 %) ozone depletion mediated by VSLBr is closely related to their fixed emissions throughout the modelled period. By including the VSLBr sources, the seasonal Halog(x-Loss) contribution to lowermost stratospheric ozone loss is practically dominated by the BrOx cycle, reflecting the low sensitivity of very short-lived (VSL) bromine to background halogen abundances to drive tropical stratospheric ozone depletion. We conclude that the link between biogenic bromine sources and seasonal changes in heterogeneous chlorine reactivation is a key feature for future projections of mid-latitude lowermost stratospheric ozone during the 21st century.