Impact of gas-to-particle partitioning approaches on the simulated radiative effects of biogenic secondary organic aerosol
Impact of gas-to-particle partitioning approaches on the simulated radiative effects of biogenic secondary organic aerosol
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DOI：
10.5194/acp-15-12989-2015
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发表时间：
2015-01-01
影响因子：
6.3
通讯作者：
Pringle, K. J.
中科院分区：
文献类型：
--
作者：
Scott, C. E.;Spracklen, D. V.;Pringle, K. J.
生物挥发性有机化合物（BVOCs）的氧化产生一系列产品，从半挥发性到极低挥发性化合物。为了处理这些二次有机蒸汽与颗粒相的相互作用，全球气溶胶微物理模型通常使用热力学分配方法（假设半挥发性氧化产物与颗粒相之间的即时平衡）或动力学方法（考虑冷凝的大小依赖性）。我们表明，生物源有机蒸汽在颗粒阶段的分配以及随之而来的物质在尺寸分布中的分布的模型处理，控制了由生物源二次有机气溶胶（SOA）引起的第一次气溶胶间接效应（AIE）的大小。采用动力学分配方法，SOA根据现有的凝聚汇进行分布，从而促进了最小粒子（即成核模式粒子）的生长。在生物源性SOA存在的情况下，这一过程倾向于增加云滴数量的浓度。相比之下，根据预先存在的有机质量分配SOA的方法限制了最小粒子的增长，从而限制了能够形成云滴的数量。通过有机介导的新粒子形成机制，应用基于质量而不是动力学的方法来划分，我们计算的生物SOA导致的全球平均AIE减少了24%。我们的研究结果表明，为了准确地描述SOA的气候效应，需要充分理解驱动有机划分的机制。
The oxidation of biogenic volatile organic compounds (BVOCs) gives a range of products, from semi-volatile to extremely low-volatility compounds. To treat the interaction of these secondary organic vapours with the particle phase, global aerosol microphysics models generally use either a thermodynamic partitioning approach (assuming instant equilibrium between semi-volatile oxidation products and the particle phase) or a kinetic approach (accounting for the size dependence of condensation). We show that model treatment of the partitioning of biogenic organic vapours into the particle phase, and consequent distribution of material across the size distribution, controls the magnitude of the first aerosol indirect effect (AIE) due to biogenic secondary organic aerosol (SOA). With a kinetic partitioning approach, SOA is distributed according to the existing condensation sink, enhancing the growth of the smallest particles, i.e. those in the nucleation mode. This process tends to increase cloud droplet number concentrations in the presence of biogenic SOA. By contrast, an approach that distributes SOA according to pre-existing organic mass restricts the growth of the smallest particles, limiting the number that are able to form cloud droplets. With an organically mediated new particle formation mechanism, applying a mass-based rather than a kinetic approach to partitioning reduces our calculated global mean AIE due to biogenic SOA by 24 %. Our results suggest that the mechanisms driving organic partitioning need to be fully understood in order to accurately describe the climatic effects of SOA.