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Temporal and spatial variations of aerosol optical properties over the Korean peninsula during KORUS-AQ
Atmospheric Environment ( IF 5 ) Pub Date : 2021-03-02 , DOI: 10.1016/j.atmosenv.2021.118301
Yongjoo Choi , Young Sung Ghim , Michal Segal Rozenhaimer , Jens Redemann , Samuel E. LeBlanc , Connor J. Flynn , Roy J. Johnson , Yonghwan Lee , Taehyoung Lee , Taehyun Park , Joshua P. Schwarz , Kara D. Lamb , Anne E. Perring

We investigated the temporal and spatial variations of aerosol optical properties over the Korean peninsula during the KORUS-AQ (KORea–United States Air Quality) experiment with ground-based aerosol optical properties measured by remote and in-situ techniques. On the ground, AErosol RObotic NETwork (AERONET) and ground-level particulate matter (PM) concentration from air quality monitoring stations were used. From the NASA DC-8 research aircraft, the airborne Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research instrument (4STAR), an aerosol mass spectrometer (AMS), and a single particle soot photometer (SP2) provided aerosol information. Average hourly fine- and coarse-mode aerosol optical depth (AOD) and fine mode fraction (FMF), were divided into four clusters (background, Seoul Metropolitan Area (SMA), southwest, and east) representing different temporal/spatial variations; the results of those clusters were similar to the clustering results using PM from air quality monitoring stations. The downwind region of SMA was dominant by light-scattering fine-mode aerosols likely due to secondary aerosol formation with high fine-mode AOD and single scattering albedo compared to other regions, even Seoul. The fine-mode aerosols were more spatially homogeneous than coarse-mode aerosols, especially in the west-to-east direction, because fine-mode aerosols are usually transported on a regional scale by westerlies rather than emitted from local emission sources. However, the aerosol size distribution was spatially more homogeneous because of a consistent contribution of fine- and coarse-mode AOD to total AOD regardless of direction between the AERONET sites. During high-aerosol loading episodes, the temporal and spatial variations of aerosol optical properties were similar to those derived from 4STAR and ground-level PM concentrations, providing detailed information on aerosol behavior and characteristics. Using missed-approach flight segments (touchdown and take-off without a full-stop), investigation of diurnal variations over the SMA revealed a significant increase in AOD and Angstrom exponent (AE) in the afternoon compared to morning and noon, especially in the downwind region, because of more active secondary formation resulting from advected and/or emitted local pollutants and precursors. The diurnal variation of PM1 in the downwind region was similar to that of AOD; it was mainly increased during the day by secondary organic aerosols and ammonium nitrate due to large amounts of isoprene and meteorological conditions that supported secondary aerosol formation. Ammonium sulfate also partially led to increasing the PM1, but its behavior was unclear, because RH decreased during the day, which would imply the reduced aqueous-phase oxidation (the major pathway for sulfate production). Compared to the downwind region, ammonium nitrate and refractory black carbon decreased in Seoul because of a slightly decreased traffic volume, dissociation of ammonium nitrate, and increased boundary layer height according to meteorological conditions in the afternoon. The results of this study provide detailed information on aerosol behavior given the synergy of the various measurement platforms used. Along with the evidence of active photochemical reactions taking place in the downwind region, such data will be useful in formulating policies that improve air quality in Korea.



中文翻译:

KORUS-AQ期间朝鲜半岛气溶胶光学特性的时空变化

我们研究气溶胶的光学特性的时空变化在与地面通过遥控器和测量气溶胶光学性质的韩美-AQ(韩国-美国空气质量)实验过程中,朝鲜半岛-现场技术。在地面上,使用了空气质量监测站的AErosol机器人网络(AERONET)和地面颗粒物(PM)浓度。来自NASA DC-8研究飞机的空中扫描光谱仪,太阳跟踪大气研究仪(4STAR),气溶胶质谱仪(AMS)和单颗粒烟灰光度计(SP2)提供了气溶胶信息。将每小时平均细模式和粗模式气溶胶光学深度(AOD)和细模式分数(FMF)分为代表不同时空变化的四个聚类(背景,首尔都市区(SMA),西南和东部);这些聚类的结果类似于使用空气质量监测站的PM进行聚类的结果。与其他地区(甚至首尔)相比,SMA的顺风区域主要是光散射精细模式气溶胶,这可能是由于具有高精细模式AOD和单散射反照率的二次气溶胶形成所致。精细模式的气溶胶在空间上比粗糙模式的气溶胶更均匀,特别是在东西向方向上,因为精细模式的气溶胶通常是通过西风​​在区域范围内传输的,而不是从本地排放源发出的。但是,由于精细模式和粗模式AOD对总AOD的一致贡献而与AERONET站点之间的方向无关,气溶胶尺寸分布在空间上更加均匀。在高气溶胶负荷期间,气溶胶光学特性的时空变化与从4STAR和地面PM浓度得出的变化相似,提供有关气溶胶行为和特性的详细信息。使用未进近的飞行段(着陆和起飞而没有完全停止),对SMA的昼夜变化进行调查后发现,与上午和中午相比,下午的AOD和Angstrom指数(AE)显着增加,尤其是在顺风地区,是由于平流和/或散发的局部污染物和前驱物导致更活跃的次生地层。PM的日变化 由于平流和/或散发的局部污染物和前体导致更活跃的次级形成。PM的日变化 由于平流和/或散发的局部污染物和前体导致更活跃的次级形成。PM的日变化顺风地区的1与AOD相似; 由于大量异戊二烯和支持二次气溶胶形成的气象条件,其在第二天主要由次要有机气溶胶和硝酸铵增加。硫酸铵也部分导致PM 1升高,但其行为尚不清楚,因为白天的相对湿度降低,这意味着水相氧化减少(硫酸盐产生的主要途径)。与顺风地区相比,汉城的硝酸铵和耐火黑碳有所减少,这是因为下午的交通量略有减少,硝酸铵的离解和边界层高度的增加。鉴于所使用的各种测量平台的协同作用,本研究的结果提供了有关气溶胶行为的详细信息。伴随着顺风地区发生积极的光化学反应的证据,这些数据将有助于制定改善韩国空气质量的政策。

更新日期:2021-03-02
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