Abstract. Even though the Arctic is remote, aerosol properties observed there are strongly influenced by anthropogenic emissions from outside the Arctic. This is particularly true for the so-called Arctic haze season (January through April). In summer (June through September), when atmospheric transport patterns change, and precipitation is more frequent, local Arctic, i.e. natural sources of aerosols and precursors, play an important role. Over the last decades, significant reductions in anthropogenic emissions have taken place. At the same time a large body of literature shows evidence that the Arctic is undergoing fundamental environmental changes due to climate forcing, leading to enhanced emissions by natural processes that may impact aerosol properties. In this study, we analyze nine aerosol chemical species and four particle optical properties from ten Arctic observatories (Alert, Gruvebadet, Kevo, Pallas, Summit, Thule, Tiksi, Barrow, Villum, Zeppelin) to understand changes in anthropogenic and natural aerosol contributions. Variables include equivalent black carbon, particulate sulfate, nitrate, ammonium, methanesulfonic acid, sodium, iron, calcium and potassium, as well as scattering and absorption coefficients, single scattering albedo and scattering Ångström exponent. First, annual cycles are investigated, which despite anthropogenic emission reductions still show the Arctic haze phenomenon. Second, long-term trends are studied using the Mann-Kendall Theil-Sen slope method. We find in total 28 significant trends over full station records, i.e. spanning more than a decade, compared to 17 significant decadal trends. The majority of significantly declining trends is from anthropogenic tracers and occurred during the haze period, driven by emission changes between 1990 and 2000. For the summer period, no uniform picture of trends has emerged. Twenty-one percent of trends, i.e. eleven out of 57, are significant, and of those five are positive and six are negative. Negative trends include not only anthropogenic tracers such as equivalent black carbon at Kevo, but also natural indicators such as methanesulfonic acid and non-sea salt calcium at Alert. Positive trends are observed for sulfate at Zeppelin and Gruvebadet. No clear evidence of a significant change in the natural aerosol contribution can be observed yet. However, testing the sensitivity of the Mann-Kendall Theil-Sen method, we find that monotonic changes of around 5 % per year in an aerosol property are needed to detect a significant trend within one decade. This highlights that long-term efforts well beyond a decade are needed to capture smaller changes. It is particularly important to understand the ongoing natural changes in the Arctic, where interannual variability can be high, such as with forest fire emissions and their influence on the aerosol population. To investigate the climate-change induced influence on the aerosol population and the resulting climate feedback, long-term observations of tracers more specific to natural sources are needed, as well as of particle microphysical properties such as size distributions, which can be used to identify changes in particle populations which are not well captured by mass-oriented methods such as bulk chemical composition.

中文翻译：

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来自十个天文台的泛北极季节周期和气溶胶特性的长期趋势

摘要。尽管北极很遥远，但在那里观察到的气溶胶特性受到北极以外人为排放的强烈影响。对于所谓的北极雾霾季节（1 月至 4 月）尤其如此。在夏季（6 月至 9 月），当大气传输模式发生变化且降水更加频繁时，当地的北极，即气溶胶和前体的天然来源，发挥着重要作用。在过去的几十年里，人为排放量显着减少。与此同时，大量文献表明，由于气候强迫，北极正在经历根本性的环境变化，导致可能影响气溶胶特性的自然过程排放增加。在这项研究中，我们分析了来自十个北极天文台（Alert、Gruvebadet、Kevo、Pallas、Summit、Thule、Tiksi、Barrow、Villum、Zeppelin）的九种气溶胶化学物质和四种粒子光学特性，以了解人为和自然气溶胶贡献的变化。变量包括当量黑碳、颗粒硫酸盐、硝酸盐、铵、甲磺酸、钠、铁、钙和钾，以及散射和吸收系数、单次散射反照率和散射 Ångström 指数。首先，对年度周期进行了调查，尽管人为排放减少，但仍显示北极雾霾现象。其次，使用 Mann-Kendall Theil-Sen 斜率方法研究长期趋势。我们在全站记录中总共发现了 28 个显着趋势，即跨越十多年，与 17 个重要的十年趋势相比。大多数显着下降趋势来自人为示踪剂，发生在雾霾期间，受 1990 年至 2000 年排放变化的驱动。夏季期间，没有出现统一的趋势图。21% 的趋势，即 57 个中的 11 个是显着的，其中 5 个是积极的，6 个是消极的。负面趋势不仅包括 Kevo 的等效黑碳等人为示踪剂，还包括 Alert 的甲磺酸和非海盐钙等自然指标。在 Zeppelin 和 Gruvebadet 观察到硫酸盐的积极趋势。目前还没有观察到自然气溶胶贡献显着变化的明确证据。然而，测试 Mann-Kendall Theil-Sen 方法的灵敏度，我们发现气溶胶特性需要每年大约 5% 的单调变化才能在十年内检测到显着趋势。这突显出需要十年以上的长期努力来捕捉较小的变化。了解北极正在进行的自然变化尤为重要，因为这里的年际变化可能很大，例如森林火灾排放及其对气溶胶种群的影响。为了研究气候变化对气溶胶种群的影响和由此产生的气候反馈，需要对更具体于自然来源的示踪剂进行长期观察，以及颗粒微物理特性，如粒度分布、