Organic aerosol processing in tropical deep convective clouds: Development of a new model (CRM-ORG) and implications for sources of particle number
Organic aerosol processing in tropical deep convective clouds: Development of a new model (CRM-ORG) and implications for sources of particle number
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DOI：
10.1002/2015jd023551
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发表时间：
2015-10-16
影响因子：
4.4
通讯作者：
Ekman, A. M. L.
中科院分区：
文献类型：
--
作者：
Murphy, B. N.;Julin, J.;Ekman, A. M. L.
评估大气颗粒物和云之间的相互作用的困难部分是由于颗粒物的化学复杂性以及在云事件期间同时发生的过程的长度和时间尺度范围很广。新的有机物云解析模型（CRM-ORG）通过明确预测替代有机化合物的形成、运输、吸收和再释放来解决这些相互作用，这些替代有机化合物与非流体静力学三维云解析模型中的挥发性基组框架一致。CRM-ORG结合了光化学生产，有机和无机蒸汽的显式冷凝/蒸发，以及一套全面的四种不同的机制，描述了有机蒸汽和硫酸的颗粒形成。我们模拟了两个深对流云事件在亚马逊雨林在1998年3月，并比较模型的颗粒大小分布与空中观测期间的时间。该模型的预测同意与观察艾特肯模式粒子在对流外流（10-14公里），但低估成核模式粒子的一个因素的20。一个强的单独由有机蒸气形成的云中粒子的过程是必要的，以再现甚至相对较低的超细粒子数浓度（类似于1500 cm（-3））。不同的初始气溶胶负荷和初始垂直气溶胶廓线的敏感性试验表明，粒子再分布和净增益或损失的云的复杂性。在云外流的基础情况下模拟，云内粒子数浓度可以提高多达3倍，但从来没有减少超过2倍低于基础。额外的敏感性的情况下，强调有必要限制的表面张力和亲和力的有机蒸汽冰表面的估计。当温度依赖的有机表面张力引入到新的粒子形成机制，粒子的数量浓度减少了60%的云流出。这些不确定性进行了讨论，了解有机气溶胶和云之间的相互作用的其他突出的挑战。对今后的理论、实验室和现场工作提出了建议。
The difficulty in assessing interactions between atmospheric particles and clouds is due in part to the chemical complexity of the particles and to the wide range of length and timescales of processes occurring simultaneously during a cloud event. The new Cloud-Resolving Model with Organics (CRM-ORG) addresses these interactions by explicitly predicting the formation, transport, uptake, and re-release of surrogate organic compounds consistent with the volatility basis set framework within a nonhydrostatic, three-dimensional cloud-resolving model. CRM-ORG incorporates photochemical production, explicit condensation/evaporation of organic and inorganic vapors, and a comprehensive set of four different mechanisms describing particle formation from organic vapors and sulfuric acid. We simulate two deep convective cloud events over the Amazon rain forest in March 1998 and compare modeled particle size distributions with airborne observations made during the time period. The model predictions agree well with the observations for Aitken mode particles in the convective outflow (10-14 km) but underpredict nucleation mode particles by a factor of 20. A strong in-cloud particle formation process from organic vapors alone is necessary to reproduce even relatively low ultrafine particle number concentrations (similar to 1500 cm(-3)). Sensitivity tests with variable initial aerosol loading and initial vertical aerosol profile demonstrate the complexity of particle redistribution and net gain or loss in the cloud. In-cloud particle number concentrations could be enhanced by as much as a factor of 3 over the base case simulation in the cloud outflow but were never reduced by more than a factor of 2 lower than the base. Additional sensitivity cases emphasize the need for constrained estimates of surface tension and affinity of organic vapors to ice surfaces. When temperature-dependent organic surface tension is introduced to the new particle formation mechanisms, the number concentration of particles decreases by 60% in the cloud outflow. These uncertainties are discussed in light of the other prominent challenges for understanding the interactions between organic aerosols and clouds. Recommendations for future theoretical, laboratory, and field work are proposed.