Multidecadal trend analysis of in situ aerosol radiative properties around the world Atmospheric Chemistry and Physics

In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann–Kendall (MK) statistical test associated with several pre-whitening methods and with Sen's slope was used as the main trend analysis method. Comparisons with general least mean square associated with autoregressive bootstrap (GLS/ARB) and with standard least mean square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficient trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficient time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, eastern/northern Europe and the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % of sites have trends which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10-year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10-year trends are primarily found for earlier periods (10-year trends ending in 2010–2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10-year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10-year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10-year trends of the scattering coefficient – there is a shift to statistically significant negative trends in 2009–2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes.

为评估影响气候变化的气溶胶参数的演变规律，研究针对遍布五大洲的52个观测站的时间序列数据，开展了气溶胶光学特性的长期趋势分析。研究所涉及的时间序列涵盖散射系数、后向散射系数、吸收系数的实测数据，以及由此推导得到的单次散射反照率（single scattering albedo）、后向散射分数、散射与吸收安斯特朗指数（Ångström exponent），其时长至少为10年，部分观测站的序列最长可达40年。本研究采用结合多种预白化方法与森斜率（Sen's slope）检验的非参数季节性曼-肯德尔（Mann–Kendall，MK）统计检验作为核心趋势分析方法。通过与自举自回归广义最小二乘法（general least mean square associated with autoregressive bootstrap，GLS/ARB）以及标准最小二乘分析（standard least mean square analysis，LMS）的对比，验证了MK检验检出的具有统计显著性的趋势，并评估了各方法的优势与局限性。当前，欧洲与北美地区的散射系数、后向散射系数大多呈下降趋势，亚洲地区的相关趋势未达到统计显著性；极地观测站则同时存在上升与下降的趋势。北美与澳大利亚的部分观测站也存在少量上升趋势。吸收系数的时间序列同样主要呈现下降趋势。就单次散射反照率而言，52%的观测站点呈现具有统计显著性的上升趋势，主要分布在亚洲、东欧/北欧以及北极地区；22%的站点呈现具有统计显著性的下降趋势，多集中在中欧与北美中部；剩余26%的站点趋势未达到统计显著性。除了对完整时间序列的趋势进行评估外，本研究还分析了连续10年时段内的趋势演变情况。对于散射与后向散射系数，具有统计显著性的上升10年趋势主要出现在较早的时段（10年趋势的终止年份为2010–2015年），覆盖极地观测站与冒纳罗亚火山观测站（Mauna Loa）。对于多数观测站而言，当前单次散射反照率具有统计显著性的下降10年趋势，前期均伴随有统计显著性或非显著性的上升10年趋势。北美大陆的空气污染减排政策效应在散射系数的10年趋势中体现得尤为明显：美国东部与中部的所有观测站在2009–2012年出现了具有统计显著性的负趋势转变。这项覆盖广泛空间范围的气溶胶辐射特性长期趋势分析，为理解气溶胶对气候变化的潜在影响提供了重要科学视角。