Effect of sea salt aerosol on tropospheric bromine chemistry
Effect of sea salt aerosol on tropospheric bromine chemistry
复制标题
海盐气溶胶对对流层溴化学的影响
DOI：
10.5194/acp-19-6497-2019
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发表时间：
2018-11
影响因子：
6.3
通讯作者：
Lei Zhu;D. Jacob;S. Eastham;M. Sulprizio;Xuan Wang;T. Sherwen;M. Evans;Qianjie Chen;B. Alexander;T. Koenig;R. Volkamer;L. G. Huey;M. Breton;T. Bannan;C. Percival
中科院分区：
文献类型：
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作者：
Lei Zhu;D. Jacob;S. Eastham;M. Sulprizio;Xuan Wang;T. Sherwen;M. Evans;Qianjie Chen;B. Alexander;T. Koenig;R. Volkamer;L. G. Huey;M. Breton;T. Bannan;C. Percival
抽象的。溴自由基通过消耗臭氧和氧化元素汞和还原的硫物种来影响全球对流层化学。观测结果通常表明，相对于海水成分，海盐气溶胶(SSA)溴的消耗为50%，这意味着SSA脱溴可能是全球对流层溴的主要来源。然而，很难将这一大来源与海洋边界层(MBL)中观察到的相对较低的溴一氧化碳(BrO)混合比率相协调。本文介绍了GEOS-Chem全球大气化学模式中SSA脱溴的一种新的机理描述，并详细描述了卤素(氯、溴和碘)化学。我们表明，观察到的SSA脱溴水平可以以与观察到的BrO混合比一致的方式重现。来自HOBr+S(IV)非均相反应和乙醛海洋排放的溴自由基沉是调节对流层BRO水平的关键。由此产生的HBr迅速被SSA吸收并沉积。夏季对南部中纬度地区SSA脱溴的观测表明，SSA对HBr的模型吸收可能太快了。该模式成功地模拟了夏季热带和中纬度地区的自由对流层BRO，与以前的GEOS-Chem版本相比，HOBr+S(IV)反应产生的溴自由基汇被更有效的HOBr驱动的云中循环所补偿。由于更大的SSA排放和更慢的溴自由基向HBr的转化，模拟的MBL中的BRO通常在冬季比夏季高得多。模型中的一个突出问题是高估了温带冬春季的自由对流层BRO，这可能反映了在这些条件下HOBrR/HBR比率的高估，在这些条件下，HOBrR的主要来源是BrNO3的水解。
Abstract. Bromine radicals influence global tropospheric chemistry by depleting ozone and by oxidizing elemental mercury and reduced sulfur species. Observations typically indicate a 50 % depletion of sea salt aerosol (SSA) bromide relative to seawater composition, implying that SSA debromination could be the dominant global source of tropospheric bromine. However, it has been difficult to reconcile this large source with the relatively low bromine monoxide (BrO) mixing ratios observed in the marine boundary layer (MBL). Here we present a new mechanistic description of SSA debromination in the GEOS-Chem global atmospheric chemistry model with a detailed representation of halogen (Cl, Br, and I) chemistry. We show that observed levels of SSA debromination can be reproduced in a manner consistent with observed BrO mixing ratios. Bromine radical sinks from the HOBr + S(IV) heterogeneous reactions and from ocean emission of acetaldehyde are critical in moderating tropospheric BrO levels. The resulting HBr is rapidly taken up by SSA and also deposited. Observations of SSA debromination at southern midlatitudes in summer suggest that model uptake of HBr by SSA may be too fast. The model provides a successful simulation of free-tropospheric BrO in the tropics and midlatitudes in summer, where the bromine radical sink from the HOBr + S(IV) reactions is compensated for by more efficient HOBr-driven recycling in clouds compared to previous GEOS-Chem versions. Simulated BrO in the MBL is generally much higher in winter than in summer due to a combination of greater SSA emission and slower conversion of bromine radicals to HBr. An outstanding issue in the model is the overestimate of free-tropospheric BrO in extratropical winter–spring, possibly reflecting an overestimate of the HOBr∕HBr ratio under these conditions where the dominant HOBr source is hydrolysis of BrNO3.