This study investigates changes in aerosol radiative effects on two highly urbanized regions across the Euro-Mediterranean basin with respect to a natural desert region as Sahara over a decade through space-based lidar observations. The research is based on the monthly-averaged vertically-resolved aerosol optical depth (AOD) atmospheric profiles along a 1${}^{\circ }\times 1^{\circ }$ horizontal grid, obtained from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument measurements aboard the Cloud-Aerosol lidar and Infrared Pathfinder Satellite Observation (CALIPSO). To assess the variability of the anthropogenic aerosols on climate, we compared the aerosol vertical profile observations to a one-dimensional radiative transfer model in two metropolitan climate sensible hot-spots in Europe, namely the Po Valley and Benelux, to investigate the variability of the aerosol radiative effects and heating rate over ten years. The same analysis is carried out as reference on the Sahara desert region, considered subject just to natural local emission. Our findings show the efficacy of emission reduction policies implemented at government level in strongly urbanized regions. The total atmospheric column aerosol load reduction (not observed in Sahara desert region) in Po Valley and Benelux can be associated with: (i) an increase of the energy flux at the surface via direct effects confirmed also by long term surface temperature observations, (ii) a general decrease of the atmospheric column heating rate, and likely (iii) an increase in surface temperatures during a ten-year period. Summarizing, the analysis, based on the decade 2007–2016, clearly show an increase of solar irradiation under cloud-free conditions at the surface of +3.6 % and +16.6% for the Po Valley and Benelux, respectively, and a reduction of −9.0% for the Sahara Desert.

中文翻译：

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欧洲和地中海高污染地区无云条件下的气溶胶直接辐射效应：十年分析（2007-2016）

本研究通过天基激光雷达观测，调查了 10 多年来，相对于撒哈拉这样的天然沙漠地区，欧洲-地中海盆地两个高度城市化地区的气溶胶辐射影响的变化。该研究基于沿 1 度的月平均垂直分辨气溶胶光学深度 (AOD) 大气廓线。${}^{\circ }\times 1^{\circ }$水平网格，从云气溶胶激光雷达和红外探路者卫星观测 (CALIPSO) 上的具有正交极化的云气溶胶激光雷达 (CALIOP) 仪器测量中获得。为了评估人为气溶胶对气候的变异性，我们将气溶胶垂直剖面观测值与欧洲两个大都市气候敏感热点（即波谷和比荷卢经济联盟）的一维辐射转移模型进行比较，以研究气溶胶垂直剖面的变异性。十年间的气溶胶辐射效应和升温速率。对撒哈拉沙漠地区进行了相同的分析作为参考，被认为仅受自然局部发射的影响。我们的研究结果显示了在高度城市化地区政府层面实施的减排政策的有效性。波谷和比荷卢经济联盟的大气柱气溶胶总负荷减少（在撒哈拉沙漠地区未观察到）可能与：（i）通过长期地表温度观测也证实的直接效应，地表能量通量的增加，（ ii) 大气柱加热速率普遍下降，并且可能 (iii) 十年期间地表温度升高。总而言之，基于 2007-2016 十年的分析清楚地表明，在无云条件下，波谷和比荷卢经济联盟地表的太阳辐射分别增加了 +3.6% 和 +16.6%，并且减少了 -撒哈拉沙漠 9.0%。(i) 通过长期地表温度观测也证实的直接效应，地表能量通量的增加，(ii) 大气柱加热速率的普遍下降，以及可能 (iii) 在 10 年期间地表温度的增加-年期间。总而言之，基于 2007-2016 十年的分析清楚地表明，在无云条件下，波谷和比荷卢经济联盟地表的太阳辐射分别增加了 +3.6% 和 +16.6%，并且减少了 -撒哈拉沙漠 9.0%。(i) 通过长期地表温度观测也证实的直接效应，地表能量通量的增加，(ii) 大气柱加热速率的普遍下降，以及可能 (iii) 在 10 年期间地表温度的增加-年期间。总而言之，基于 2007-2016 十年的分析清楚地表明，在无云条件下，波谷和比荷卢经济联盟地表的太阳辐射分别增加了 +3.6% 和 +16.6%，并且减少了 -撒哈拉沙漠 9.0%。