Particle phase-state variability in the North Atlantic free troposphere during summertime is determined by atmospheric transport patterns and sources
Particle phase-state variability in the North Atlantic free troposphere during summertime is determined by atmospheric transport patterns and sources
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DOI：
10.5194/acp-22-9033-2022
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发表时间：
2022-07
影响因子：
6.3
通讯作者：
Zezhen Cheng;Megan Morgenstern;Bo Zhang-;M. Fraund;N. Lata;Rhenton Brimberry;M. Marcus;L. Mazzoleni;P. Fialho;S. Henning;B. Wehner;C. Mazzoleni;S. China
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文献类型：
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作者：
Zezhen Cheng;Megan Morgenstern;Bo Zhang-;M. Fraund;N. Lata;Rhenton Brimberry;M. Marcus;L. Mazzoleni;P. Fialho;S. Henning;B. Wehner;C. Mazzoleni;S. China
抽象的。对流层游离气溶胶粒子具有重要的气候效应，但由于其物理化学性质在长距离传输过程中的变化，其气候效应受到很大限制。在这项研究中，我们调查了化学成分，并概述了在2014年6月和7月，2015年和2017年在北大西洋上空进行远程传输的单个粒子的相态，以观测亚速尔群岛的皮科山（OMP）。OMP是研究远距离传输的对流层自由粒子的理想场所，因为本地排放的影响可以忽略不计，并且来自边界层的贡献很少。我们使用的FLEXible PARTicle拉格朗日粒子扩散模型（FLEXPART），以确定采样的空气质量的起源和运输轨迹，并发现他们中的大多数来自北美和北大西洋上空再循环。FLEXPART分析表明，取样的空气团年代久远（烟羽平均年龄>10天）。使用计算机控制的扫描电子显微镜与能量色散X射线光谱仪（CCSEM-EDX）和扫描透射X射线显微镜与近边X射线吸收精细结构光谱（STXM-NEXAFS）探测单个颗粒的尺寸分辨化学组成。CCSEM-EDX结果表明，最丰富的颗粒类型是碳质（29.9%至82.0%），海盐（20.3%至31.6%）和硫酸盐海盐（20.4%至31.5%）。我们使用了一个倾斜的阶段内的环境扫描电子显微镜（ESEM）接口，以确定各个亚微米颗粒的相态。我们发现，由于无机夹杂物，大多数颗粒（约47%至99%）在收集时处于液态。此外，我们还观察到固体和半固体颗粒的相当大的比例（分别为10%至30%和101%至42%），在不同的传输模式和事件，反映了颗粒的相态变化为不同的大气传输事件和来源。相态测量与FLEXPART CO示踪剂分析相结合，我们发现野火影响的羽流可以导致在自由对流层中长距离传输后的颗粒具有广泛的粘度。我们还使用了从全球预报系统（GFS）提取的温度和相对湿度值沿着FLEXPART模拟路径来预测颗粒在运输过程中的相态，发现忽略与无机物的内部混合会导致高估自由对流层颗粒的粘度。我们的研究结果保证未来的调查，旨在定量评估内部混合对单个颗粒的相态的影响。这项研究还提供了对自由对流层颗粒的化学组成和相态的见解，这可以帮助模型减少环境气溶胶颗粒对气候影响的不确定性。
Abstract. Free tropospheric aerosol particles have important but poorly constrained climate effects due to transformations of their physicochemical properties during long-range transport. In this study, we investigate the chemical composition and provide an overview of the phase states of individual particles that have undergone long-range transport over the North Atlantic Ocean in June and July 2014, 2015, and 2017 to the Observatory of Mount Pico (OMP) in the Azores. The OMP is an ideal site for studying long-range-transported free tropospheric particles because local emissions have a negligible influence and contributions from the boundary layer are rare. We used the FLEXible PARTicle Lagrangian particle dispersion model (FLEXPART) to determine the origins and transport trajectories of sampled air masses and found that most of them originated from North America and recirculated over the North Atlantic Ocean. The FLEXPART analysis showed that the sampled air masses were highly aged (average plume age >10 d). Size-resolved chemical compositions of individual particles were probed using computer-controlled scanning electron microscopy with an energy-dispersive X-ray spectrometer (CCSEM-EDX) and scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS). CCSEM-EDX results showed that the most abundant particle types were carbonaceous (∼ 29.9 % to 82.0 %), sea salt (∼ 0.3 % to 31.6 %), and sea salt with sulfate (∼ 2.4 % to 31.5 %). We used a tilted stage interfaced within an environmental scanning electron microscope (ESEM) to determine the phase states of individual submicron particles. We found that most particles (∼ 47 % to 99 %) were in the liquid state at the time of collection due to inorganic inclusions. Moreover, we also observed substantial fractions of solid and semisolid particles (∼ 0 % to 30 % and ∼ 1 % to 42 %, respectively) during different transport patterns and events, reflecting the particles' phase-state variability for different atmospheric transport events and sources. Combining phase state measurements with FLEXPART CO tracer analysis, we found that wildfire-influenced plumes can result in particles with a wide range of viscosities after long-range transport in the free troposphere. We also used temperature and RH values extracted from the Global Forecast System (GFS) along the FLEXPART-simulated path to predict the phase state of the particles during transport and found that neglecting internal mixing with inorganics would lead to an overestimation of the viscosity of free tropospheric particles. Our findings warrant future investigation aiming at the quantitative assessment of the influence of internal mixing on the phase states of the individual particles. This study also provides insights into the chemical composition and phase state of free tropospheric particles, which can help models to reduce uncertainties about the effects of ambient aerosol particles on climate.