Modeling heterogeneous sulphate production in maritime stratiform clouds
Modeling heterogeneous sulphate production in maritime stratiform clouds
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模拟海洋层状云中异质硫酸盐的产生
DOI：
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发表时间：
2000
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通讯作者：
S. Clegg
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作者：
C. O’Dowd;J. Lowe;Nicola A. Clegg;Michael H. Smith;S. Clegg
本文建立了一个与拉格朗日网格相联系的液滴尺度物理化学模式，并用于研究海洋层状云中非均匀硫酸盐的产生过程。该模型研究提供了一个严格的方法来处理云化学处理的非理想化学的水相平衡和液滴生长的Pitzer方法，以克服替代热力学方法的许多缺点。此外，目前的研究使用海盐气溶胶的多模态表示，而不是在大多数以前的工作中使用的单一模式。模型模拟的结果表明，在气溶胶大小范围内，硫酸盐的产生分布是非线性的，硫酸盐的很大一部分（约75-90%）是在海盐气溶胶颗粒上形成的液滴中产生的。海盐颗粒的数量影响了产生的硫酸盐总量和在非海盐硫酸盐气溶胶周围形成的云滴上产生的分数。溶解臭氧和过氧化氢都是重要的氧化剂物种，虽然臭氧驱动的氧化途径是占主导地位的海盐气溶胶颗粒上形成的液滴。硫酸盐的产生率被认为是一个非线性函数的气体二氧化硫浓度在云底和只有非常弱的硫酸盐核浓度的依赖。在云中和云下硫酸盐生产的比较表明，海盐核中的硫酸盐生产不受碳酸盐缓冲的限制，并且由于云的“虚拟”缓冲能力，云内生产可以超过无云生产的许多倍。使用非理想溶液效应似乎很重要，特别是对于清洁到中度污染的SO2浓度（<500万亿分之一）和海盐核存在时，与理想溶液模拟相比，硫酸盐产量至少降低40%。
A size-resolved droplet physico chemical model linked to a Lagrangian parcel framework was developed and used to study the heterogeneous sulphate production process in marine stratiform clouds. This model study provides a rigorous approach to cloud chemistry processing by treating the effects of non ideal chemistry on both aqueous phase equilibration and droplet growth using the Pitzer method to overcome many of the shortcomings of alternative thermodynamic methods. In addition, the current study uses a multi modal representation of sea-salt aerosol, rather than the single mode used in most previous work. The results of the model simulations showed a distribution of sulphate production across the aerosol size range that was non linear and that a significant fraction (≈ 75–90%) of the sulphate was produced in droplets formed on sea-salt aerosol particles. The number of sea-salt particles affected both the total amount of sulphate produced and the fraction produced on cloud droplets formed around non-sea-salt sulphate aerosol. Dissolved ozone and hydrogen peroxide were both important as oxidant species, although the ozone-driven oxidation pathway was dominant in droplets formed on sea-salt aerosol particles. The rate of sulphate production was found to be a non linear function of the gaseous sulphur dioxide concentration at cloud base and only very weakly dependent on sulphate nuclei concentration. A comparison of sulphate production in cloud and below cloud indicates that sulphate production in sea-salt nuclei is not limited by the carbonate buffer and that in-cloud production can exceed, many times, that of cloud-free production due to the “virtual” buffering capacity of the cloud. The use of non ideal solution effects appear important, particularly for clean-to-moderately polluted SO2 concentrations (<500 parts per trillion) and when sea-salt nuclei are present, resulting in at least 40% lower sulphate production when compared to ideal solution simulations.