Modelling wintertime sea-spray aerosols under Arctic haze conditions
Modelling wintertime sea-spray aerosols under Arctic haze conditions
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DOI：
10.5194/acp-23-5641-2023
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发表时间：
2023-05
影响因子：
6.3
通讯作者：
E. Ioannidis;K. Law;Jean-Christophe Raut;L. Marelle;T. Onishi;R. Kirpes;L. Upchurch;T. Tuch;A. Wiedensohler;A. Massling;H. Skov;P. Quinn;K. Pratt
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作者：
E. Ioannidis;K. Law;Jean-Christophe Raut;L. Marelle;T. Onishi;R. Kirpes;L. Upchurch;T. Tuch;A. Wiedensohler;A. Massling;H. Skov;P. Quinn;K. Pratt
摘要。人为和自然排放导致北极冬季和早春气溶胶浓度增加，人们最关注的是造成所谓北极雾霾的人为气溶胶。研究较少的北极雾霾条件下的冬季海洋喷雾气溶胶（SSAs）是本研究的重点，因为它们可以对冬季北极气溶胶丰度做出重要贡献。现场活动数据分析显示，有证据表明，2014年冬季，美国阿拉斯加北部Utqiaġvik（以前称为Barrow）的海洋有机物增加了ssa的本地来源。模型倾向于低估北极冬季的亚微米SSA而高估超微米SSA，包括本文使用的天气研究预报耦合化学（WRF-Chem）模型的基础版本，其中包括基于Gong等人（1997）的广泛使用的SSA源函数。2014年冬季的准半球模拟，包括更新的风速和海表温度（SST） SSA排放依赖关系以及海洋海盐有机物和海盐硫酸盐的来源，与北极偏远地区的观测结果相比，显著提高了模式性能，尤其是粗模式钠和氯，它们的含量降低了。改进的模型还模拟了不同地点ssa对无机气溶胶的更实际贡献，在观测值中从20%到93%不等。三分之二的模型性能改进来自于对海表温度的依赖。硝酸盐气溶胶的模拟也得到了改进，因为在粗模式下，ssa对硝酸的非均匀吸收减少了，而在细模式下，硝酸盐的吸收增加了。这突出了天然SSAs与造成北极雾霾的无机人为气溶胶之间相互作用的重要性。与观测结果相比，有机气溶胶和海盐硫酸盐组分的模拟也得到了改进。然而，该模式低估了在一些北极站点（特别是Utqiaġvik）观测到的SSA组分和亚微米非海盐硫酸盐浓度升高的事件。在2014年1月和2月的Utqiaġvik现场活动期间，在阿拉斯加北部进行了更高分辨率的运行，探索了可能的原因。根据活动数据，当地海盐海洋有机物来源的增加，增加了阿拉斯加北部的模拟有机气溶胶。然而，与以前现有数据的比较表明，该模型低估了来自开放引线的当地自然来源以及当地人为来源。当地人为来源的缺失也可以解释Utqiaġvik低模拟（亚微米）非海盐硫酸盐。同样基于北极数据，引入了对亚微米SSA排放的更高风速依赖，减少了模拟亚微米SSA的偏差，而海冰部分，包括开放的引线，被证明是控制模拟阿拉斯加北海岸的超微米SSA的重要因素，而不是亚微米SSA。本文给出的区域结果表明，模拟的ssa对风速依赖更为敏感，但需要对海冰分布进行真实的模拟，以模拟局部ssa，包括海洋生物。该研究支持Utqiaġvik野外活动的发现，即开放的铅是Utqiaġvik冬季新鲜和老化的ssa（包括海洋有机气溶胶）的主要来源；这些发现并不表明吹雪和吹霜花会产生影响。为了改进北极冬季气溶胶的模式模拟，需要关于影响冬季SSA产生过程的新现场数据，特别是精细模式气溶胶的数据，同时也需要提高对可能的当地人为来源的了解。
Abstract. Anthropogenic and natural emissions contribute to enhanced concentrations of aerosols in the Arctic winter and early spring, with most attention being paid to anthropogenic aerosols that contribute to so-called Arctic haze. Less-well-studied wintertime sea-spray aerosols (SSAs) under Arctic haze conditions are the focus of this study, since they can make an important contribution to wintertime Arctic aerosol abundances. Analysis of field campaign data shows evidence for enhanced local sources of SSAs, including marine organics at Utqiaġvik (formerly known as Barrow) in northern Alaska, United States, during winter 2014. Models tend to underestimate sub-micron SSAs and overestimate super-micron SSAs in the Arctic during winter, including the base version of the Weather Research Forecast coupled with Chemistry (WRF-Chem) model used here, which includes a widely used SSA source function based on Gong et al. (1997). Quasi-hemispheric simulations for winter 2014 including updated wind speed and sea-surface temperature (SST) SSA emission dependencies and sources of marine sea-salt organics and sea-salt sulfate lead to significantly improved model performance compared to observations at remote Arctic sites, notably for coarse-mode sodium and chloride, which are reduced. The improved model also simulates more realistic contributions of SSAs to inorganic aerosols at different sites, ranging from 20 %–93 % in the observations. Two-thirds of the improved model performance is from the inclusion of the dependence on SSTs. The simulation of nitrate aerosols is also improved due to less heterogeneous uptake of nitric acid on SSAs in the coarse mode and related increases in fine-mode nitrate. This highlights the importance of interactions between natural SSAs and inorganic anthropogenic aerosols that contribute to Arctic haze. Simulation of organic aerosols and the fraction of sea-salt sulfate are also improved compared to observations. However, the model underestimates episodes with elevated observed concentrations of SSA components and sub-micron non-sea-salt sulfate at some Arctic sites, notably at Utqiaġvik. Possible reasons are explored in higher-resolution runs over northern Alaska for periods corresponding to the Utqiaġvik field campaign in January and February 2014. The addition of a local source of sea-salt marine organics, based on the campaign data, increases modelled organic aerosols over northern Alaska. However, comparison with previous available data suggests that local natural sources from open leads, as well as local anthropogenic sources, are underestimated in the model. Missing local anthropogenic sources may also explain the low modelled (sub-micron) non-sea-salt sulfate at Utqiaġvik. The introduction of a higher wind speed dependence for sub-micron SSA emissions, also based on Arctic data, reduces biases in modelled sub-micron SSAs, while sea-ice fractions, including open leads, are shown to be an important factor controlling modelled super-micron, rather than sub-micron, SSAs over the north coast of Alaska. The regional results presented here show that modelled SSAs are more sensitive to wind speed dependence but that realistic modelling of sea-ice distributions is needed for the simulation of local SSAs, including marine organics. This study supports findings from the Utqiaġvik field campaign that open leads are the primary source of fresh and aged SSAs, including marine organic aerosols, during wintertime at Utqiaġvik; these findings do not suggest an influence from blowing snow and frost flowers. To improve model simulations of Arctic wintertime aerosols, new field data on processes that influence wintertime SSA production, in particular for fine-mode aerosols, are needed as is improved understanding about possible local anthropogenic sources.