van Herpen Maarten M J W, Li Qinyi, Saiz-Lopez Alfonso, Liisberg Jesper B, Röckmann Thomas, Cuevas Carlos A, Fernandez Rafael P, Mak John E, Mahowald Natalie M, Hess Peter, Meidan Daphne, Stuut Jan-Berend W, Johnson Matthew S
Acacia Impact Innovation, Maarten van Herpen, Bernheze 5384 BB, The Netherlands.
Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Blas Cabrera, Spanish National Research Council, 28006 Madrid, Spain.
Proc Natl Acad Sci U S A. 2023 Aug;120(31):e2303974120. doi: 10.1073/pnas.2303974120. Epub 2023 Jul 24.
Active chlorine in the atmosphere is poorly constrained and so is its role in the oxidation of the potent greenhouse gas methane, causing uncertainty in global methane budgets. We propose a photocatalytic mechanism for chlorine atom production that occurs when Sahara dust mixes with sea spray aerosol. The mechanism is validated by implementation in a global atmospheric model and thereby explaining the episodic, seasonal, and location-dependent C depletion in CO in air samples from Barbados [J.E. Mak, G. Kra, T. Sandomenico, P. Bergamaschi, (2003)], which remained unexplained for decades. The production of Cl can also explain the anomaly in the CO:ethane ratio found at Cape Verde [K. A. Read et al., (2009)], in addition to explaining the observation of elevated HOCl [M. J. Lawler et al., , 7617-7628 (2011)]. Our model finds that 3.8 Tg(Cl) y is produced over the North Atlantic, making it the dominant source of chlorine in the region; globally, chlorine production increases by 41%. The shift in the methane sink budget due to the increased role of Cl means that isotope-constrained top-down models fail to allocate 12 Tg y (2% of total methane emissions) to C-depleted biological sources such as agriculture and wetlands. Since 2014, an increase in North African dust emissions has increased the C isotope of atmospheric CH, thereby partially masking a much greater decline in this isotope, which has implications for the interpretation of the drivers behind the recent increase of methane in the atmosphere.
大气中的活性氯含量难以精确测定，其在强效温室气体甲烷氧化过程中的作用也不明确，这导致全球甲烷收支存在不确定性。我们提出了一种光催化机制，用于解释撒哈拉沙尘与海喷雾气溶胶混合时产生氯原子的过程。该机制通过在全球大气模型中的应用得到验证，从而解释了巴巴多斯空气样本中一氧化碳（CO）出现的偶发性、季节性和位置依赖性碳（C）消耗现象[J.E. 马克、G. 克拉、T. 桑多梅尼科、P. 贝加马斯基，（2003年）]，几十年来这一现象一直无法得到解释。氯的产生还可以解释佛得角发现的一氧化碳与乙烷比例异常现象[K.A. 里德等人，（2009年）]，此外还能解释次氯酸（HOCl）浓度升高的观测结果[M.J. 劳勒等人，，7617 - 7628（2011年）]。我们的模型发现，北大西洋每年产生3.8太克（Tg）（Cl），使其成为该地区氯的主要来源；在全球范围内，氯的产量增加了41%。由于氯的作用增强，甲烷汇收支的变化意味着同位素约束的自上而下模型无法将12太克/年（占甲烷总排放量的2%）分配到碳消耗的生物源，如农业和湿地。自2014年以来，北非沙尘排放增加，导致大气中甲烷的碳同位素增加，从而部分掩盖了该同位素更大幅度的下降，这对解释近期大气中甲烷增加背后的驱动因素具有重要意义。
