Abstract Although urban aerosols have been extensively explored, the variation of aerosols across space and time in the city and its underlying mechanism have not been quantitatively understood. This study defined the phenomenon of higher aerosols concentrations in the urban areas than in the surrounding rural areas as “Urban Aerosol Pollution Island (UAPI)” and quantified UAPI intensity using the urban-rural difference of Particulate Matter (PM10) concentrations. We investigated the diurnal and seasonal variations of UAPI and its relationship with Urban Heat Island (UHI) in the metropolitan area of Berlin using the combination of a long-term (2010– 2017) observation network and the WRF-Chem model. Observation data showed that UAPI existed at most of time, with more than one-quarter of the days showing daily mean UAPI intensity of more than 5 μg/m3 and 10.6 μg/m3, respectively at background and traffic stations. The PM10 concentrations and UAPI intensity at background stations showed opposite diurnal variations, with higher PM10 concentrations at night, but larger UAPI intensity in the daytime. Seasonally, both PM10 concentrations and UAPI showed larger values in winter. The seasonal variation of UAPI intensity was closely related to the air temperature. The colder days in winter and hotter days with heat wave in summer showed larger UAPI intensity. The UAPI was negatively correlated to UHI in summer. The mitigation of UHI increased PM10 concentrations in urban areas by ~3%, leading to a stronger UAPI. This study can contribute to the accurate risk assessment of aerosol pollution and the design of mitigation strategies.

中文翻译：

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城市气溶胶污染岛的时间变化及其与城市热岛的关系

摘要 尽管城市气溶胶已被广泛探索，但城市气溶胶跨时空变化及其潜在机制尚未得到定量理解。本研究将城市地区气溶胶浓度高于周边农村地区的现象定义为“城市气溶胶污染岛（UAPI）”，并使用颗粒物（PM10）浓度的城乡差异量化UAPI强度。我们结合长期（2010-2017 年）观测网络和 WRF-Chem 模型研究了 UAPI 的日变化和季节变化及其与柏林大都市区的城市热岛（UHI）的关系。观察数据显示UAPI存在的时间最多，超过四分之一的天数显示背景站和交通站的日平均 UAPI 强度分别超过 5 μg/m3 和 10.6 μg/m3。背景站 PM10 浓度和 UAPI 强度呈相反的昼夜变化，夜间 PM10 浓度较高，但白天 UAPI 强度较大。季节性地，PM10 浓度和 UAPI 在冬季都显示出较大的值。UAPI强度的季节性变化与气温密切相关。冬季较冷的日子和夏季较热的日子有热浪表现出较大的UAPI强度。夏季 UAPI 与 UHI 呈负相关。UHI 的缓解使城市地区的 PM10 浓度增加了约 3%，导致 UAPI 更强。