Elevated Anthropogenic Contributions to Trace Elements in Marine Aerosols Compared to Coastal Qingdao in Eastern China

Long-range transport of trace elements (TEs) by aerosols plays a critical role in modulating marine biogeochemistry; yet, their source contributions and spatial variability across land-sea gradients remain poorly constrained. Here, we investigate TEs (e.g., Fe, Mn, Cr, V, Ni, Cu, Zn, As, Pb, Cd) in PM_2.5 aerosols collected from the coastal city of Qingdao (eastern China) and adjacent offshore regions (Bohai Sea and Yellow Sea) during spring and summer 2018, to quantify terrestrial vs. marine source contributions and unravel key drivers of their spatial patterns. All TEs exhibited higher concentrations in Qingdao than in offshore marine areas in spring, whereas Zn, Pb, As, and Cd (52.5–78.8% from coal combustion over the marine areas) reversed to higher concentrations in offshore marine areas than in Qingdao in summer, indicating intensified anthropogenic impact on the marine atmosphere. For traditional crustal TEs (Fe, Mn, Cr), terrestrial dust dominated in spring Qingdao (e.g., Fe: 62.3%, 148.6 ng m^-3), but dust contributions declined sharply in spring offshore marine areas (Fe: 16.8%, 52.3 ng m^-3). Instead, coal combustion emerged as the dominant source in summer offshore marine aerosols (Fe: 43.2%, 82.8 ng m^-3), exceeding its contribution to Qingdao (Fe: 14.45%, 45.46 ng m^-3). Ship emissions dominated sources of Ni and V (V: 81.2% in spring, 90.5% in summer) and contributed significantly to Fe, Mn, and Cr, particularly in summer offshore aerosols (e.g., Fe: 27.4%, 52.5 ng m^-3). Spring offshore marine aerosols showed elevated sea salt contributions to Fe, Mn, Zn, Cd, and Pb (18.5–33.6%), indicating extensive multi-source mixing (dust, sea salt, and anthropogenic sources); the biogeochemical implications of this mixing for element reactivity warrant further investigation. These findings highlight the dominant role of anthropogenic emissions (coal combustion and shipping) in shaping the TE composition of offshore aerosols over the Bohai and Yellow Seas. This work advances our understanding of land-sea interactions in atmospheric TE cycling and offers critical constraints for regional air quality and climate models.

中国东部近海区域大气气溶胶中的微量元素（Trace elements, TEs）同时源自陆地与海洋排放源。然而，其随源区变化的分布特征仍尚未被充分阐明。
2018年春夏季期间，研究团队于中国东部沿海城市青岛及邻近的渤海、黄海海域采集了PM₂.₅样品，随后按源区对微量元素进行定量分析与溯源解析。春季时段，陆源气溶胶中的微量元素浓度显著更高。地壳粉尘对Fe、Mn、Cr和Ni的贡献率达39.2%~77.8%；而废弃物与工业排放对Cu、Zn和Pb的贡献率为29.4%~70.1%。西风将人为源微量元素输送至近海区域：海洋气溶胶中，燃煤燃烧对As、Cd、Pb、Zn和Cr的贡献率为25.9%~61.4%，燃油燃烧对V和Ni的贡献率达58.6%~84.4%，这表明污染物可实现高效的长距离传输。
夏季时段，粉尘的影响有所减弱。在青岛地区，生物质燃烧对Zn、Cd、Pb和Cr的贡献率为38.2%~46.3%，而机动车排放主导了As和Cu的来源（占比41.7%~57.3%）。在海洋区域，人为源元素（Zn、As和Cd）的浓度偶尔会超过沿海水平，其中燃煤燃烧仍为主要贡献源（贡献率40.8%~75.5%）。船舶排放的贡献尤为突出，近海区域V和Ni的79.3%与63.3%均来自船舶排放。东南风将船舶排放的污染物输送至沿海区域，与春季相比（Fe和Mn占比分别为1.9%和1.8%），夏季Fe（21.2%）与Mn（14.0%）的占比显著提升。
本研究结果揭示了海陆梯度下微量元素来源的显著季节变化，凸显了人为活动对海洋气溶胶的影响日益增强，其中尤以燃煤燃烧与海运船舶排放的影响最为突出。定量解析这些源贡献有助于评估其对海洋生物地球化学过程的影响，并可为针对性污染防控提供科学支撑。