A global model study of processes controlling aerosol size distributions in the Arctic spring and summer
A global model study of processes controlling aerosol size distributions in the Arctic spring and summer
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DOI：
10.1029/2007jd009114
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发表时间：
2008-04
影响因子：
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通讯作者：
H. Korhonen;K. Carslaw;D. Spracklen;D. Ridley;J. Ström
中科院分区：
文献类型：
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作者：
H. Korhonen;K. Carslaw;D. Spracklen;D. Ridley;J. Ström
[1]我们使用一个全球化学传输模型（CTM）与尺寸分辨气溶胶微物理来评估我们的理解控制北极气溶胶的过程中，侧重于从春季北极雾霾到夏季清洁条件的过渡过程中的颗粒尺寸分布的季节性变化。这一时期对全球模型模拟提出了若干挑战，因为气象变化影响到传输路径和降水清除率，与海冰破裂和生物活动增加有关的微量气体和微粒的海洋-大气通量变化，以及光解和氧化速率变化可能影响微粒成核和生长速率。观测结果表明，这些变化导致从一个积累模式为主的气溶胶在春季到一个占主导地位的艾特肯和成核模式粒子在夏季。我们发现，遥远的北极气溶胶粒径分布是非常敏感的模型处理的湿去除。为了模拟冬季和春季典型的高累积模式浓度，有必要在运输过程中大大减少这些颗粒的清除。由此产生的积累模式的增加导致改善模型艾特肯模式粒子浓度（下降，由于在自由对流层清除增加），并产生气溶胶光学厚度与观测良好的协议。成核和艾特肯模式粒子的夏季增加是一致的本地气溶胶成核率的变化，主要是由增加的硫酸蒸汽的光化学生产，并在较小程度上，减少在冷凝汇作为北极雾霾减少。另外，要解释所观察到的夏季艾特肯模式的超细海雾粒子的粒子浓度，需要一个海-气通量的一个因素5- 25大于当前风速和海面温度依赖通量参数化预测。增强的总通量明显高于在北极测得的，并不能解释在高北极观测到的成核模式。模式表明，夏季Aitken粒子源对气溶胶光学厚度和累积模式的影响很小，但在上升气流速度大于15 cm/s的云中，它们可能对云凝结核有贡献。从全球气溶胶建模的角度来看，我们对北极气溶胶的了解很少。我们提出了几个过程，目前限制了我们的能力，模拟这种具有挑战性的环境。
[1] We use a global chemical transport model (CTM) with size-resolved aerosol microphysics to evaluate our understanding of the processes that control Arctic aerosol, focussing on the seasonal changes in the particle size distribution during the transition from Arctic haze in spring to cleaner conditions in summer. This period presents several challenges for a global model simulation because of changes in meteorology, which affect transport pathways and precipitation scavenging rates, changes in the ocean-atmosphere flux of trace gases and particulates associated with sea ice break-up and increased biological activity, and changes in photolysis and oxidation rates which can affect particle nucleation and growth rates. Observations show that these changes result in a transition from an accumulation mode-dominated aerosol in spring to one dominated by Aitken and nucleation mode particles in summer. We find that remote Arctic aerosol size distribution is very sensitive to the model treatment of wet removal. In order to simulate the high accumulation mode concentrations typical of winter and spring it was necessary to substantially reduce the scavenging of these particles during transport. The resulting increases in accumulation mode lead to improvement in the modeled Aitken mode particle concentrations (which fall, due to increased scavenging in the free troposphere) and produce aerosol optical depths in good agreement with observations. The summertime increase in nucleation and Aitken mode particles is consistent with changes in local aerosol nucleation rates driven mainly by increased photochemical production of sulphuric acid vapor and, to a lesser extent, by decreases in the condensation sink as Arctic haze decreases. Alternatively, to explain the observed summertime Aitken mode particle concentrations in terms of ultrafine sea spray particles requires a sea-air flux a factor 5–25greater than predicted by current wind speed and sea surface temperature dependent flux parameterizations. The enhanced total flux is clearly higher than measured in the Arctic and cannot explain the observed nucleation mode in the high Arctic. The model suggests that the summertime source of Aitken particles has very little effect on the accumulation mode and aerosol optical depth but they may contribute to cloud condensation nuclei in clouds with updraught velocities greater than about 15 cm/s. From a global aerosol modeling perspective, our understanding of Arctic aerosol is poor. We suggest several processes that currently limit our ability to simulate this challenging environment.