Data_Sheet_1_Contribution of Saharan Dust to Ion Deposition Loads of High Alpine Snow Packs in Austria (1987–2017).PDF

We investigate the influence of Saharan dust on the chemical composition and deposition loads of a 31-year long snow chemistry data set (1987–2017) of high alpine snow packs situated close to the Sonnblick Observatory, a global GAW (Global Atmospheric Watch) station, in the National Park Hohe Tauern in the Austrian Alps. Based on the snow pack of the winter accumulation period 2015/2016, when two Saharan dust events were visible by a reddish color of the snow, we define a pH > 5.6 together with a Ca2+ concentration > 10 μeq/l as thresholds to identify Saharan dust affected snow layers. This criterion is checked with an intercomparison with trajectories and on-line aerosol data determined at the Sonnblick Observatory. This check was extended to the accumulation periods 2014/2015 and 2016/2017 before the whole time series is investigated regarding the contribution of Saharan dust to ion deposition loads. Especially Mg2+, Ca2+, and H+ depositions are strongly affected by Saharan dust input causing, as average values across the 30 years period, increased Mg2+ (25%) and Ca2+ (35%) contributions of affected snow layers, while the contribution to the snow water equivalent was only 11%. For H+ Saharan dust affected snow layers show a much lower contribution (2%) while the contribution of other ions is well comparable to the deposition amount expected according to the snow water equivalent of affected snow layers. The pH range of Saharan dust affected snow layers covers 5.58–7.17, while the median value of all samples is 5.40. The long term trends of ion deposition are not affected by the deposition of Saharan dust.

本研究针对毗邻全球大气监测（Global Atmospheric Watch，GAW）站点松布利克观测站、位于奥地利阿尔卑斯陶恩山国家公园内的高海拔积雪层，基于1987年至2017年共计31年的积雪化学数据集，探究撒哈拉沙尘对积雪化学组成与沉降负荷的影响。基于2015/2016年冬季积雪积累期的观测数据——该时段内两次撒哈拉沙尘事件可通过积雪呈现红褐色直观识别——本研究设定pH值大于5.6且Ca²+浓度大于10 μeq/l作为判定受撒哈拉沙尘影响积雪层的阈值标准。该判定标准通过与松布利克观测站获取的大气气团轨迹及在线气溶胶监测数据开展比对验证，并将验证范围扩展至2014/2015与2016/2017两个积雪积累期，随后对完整时间序列展开分析，以明确撒哈拉沙尘对各离子沉降负荷的贡献占比。研究结果显示，Mg²+、Ca²+与H+的沉降过程受撒哈拉沙尘输入的显著影响：以30年观测周期的平均水平计，受沙尘影响的积雪层中Mg²+与Ca²+的沉降贡献占比分别提升25%与35%，而其对积雪水当量的贡献占比仅为11%；对于H+而言，受撒哈拉沙尘影响的积雪层其贡献占比仅为2%，其余离子的沉降贡献则与受影响积雪层的积雪水当量所对应的理论沉降量基本一致。受撒哈拉沙尘影响的积雪层pH值区间为5.58至7.17，而所有样本的pH中位数为5.40。撒哈拉沙尘的沉降并未对离子沉降的长期趋势产生显著影响。