COMBLE-ISLAS water isotopes in precipitation (COMBLEISLASISO)

During the measurement period, precipitation was sampled on daily to sub-daily basis with a sampling kit consiting of a clear plastic box (60x40x40 cm) mounted to a ground structure. Daily sampling lasted from 22 Feb to 24 Mar 2020. At a fixed time of day (10 UTC), samples were collected and the sampling box cleaned for the next sample. Additionally, during intense observations periods (IOPs) announced by ISLAS, ARMS scientists increased sampling frequency to sub-daily sampling. During the campaign period, 2 IOPs were conducted, with in total 12 samples taken. IOP1 lasted from 27 Feb 10 to 02 Mar 2020, and IOP2 lasted from 12 Mar to 14 Mar 2020. Solid precipitation in the box was then melted, transferred to an 8 ml glass vial, sealed and shipped to FARLAB (University of Bergen, Norway) for stable water isotope analysis. Measured stable isotope composition of precipitation samples will be related to conditions at other sampling locations, and at the evaporation site to inform about conservation of water isotope quantities. In the period from 22 Feb to 24 Mar, 23 daily samples were collected at 10 UTC for stable water isotope analysis. During the entire sampling period, a high variability of precipitation phase was encountered. Most samples were recovered in the form of graupel/snow (12 samples), as rain (7 samples), and the remaining samples fell as graupel, snow, rain or frozen rain. Precipitation amounts varied between <1 mm (26 Feb) and 140 mm (25 Feb) within the sampling box. Furthermore, higher-resolution sampling was conducted during 2 intense observation periods (IOPs). During IOP1, lasting from 27 Feb 10 UTC to 02 Mar 10 UTC, 7 samples were collected, all of them as solid phase precipitation. IOP2 lasted from 12 Mar 10 UTC to 14 Mar 09 UTC, and 5 samples (all as graupel/snow) were collected. Samples were processed according to FARLAB standard measurement procedures. In short, samples were transferred to 1.5 ml glass vials with rubber/PTFE septa (part #548-0907, VWR, USA). An autosampler (A0325, Picarro Inc) transferred ca. 2µl per injection into a high-precision vapourizer (A0211, Picarro Inc, USA) heated to 110°C. After blending with dry N2 (< 5 ppm H2O) the gas mixture was directed into the measurement cavity of a Cavity-Ring Down Spectrometer (L2140-i, Picarro Inc) for about 7 min with a typical water concentration of 20 000 ppm. Memory effects were reduced by two times measuring a vapour mixture at a mixing ratio of 50 000 ppm, obtained from 2 injections of 2 µl for 5 min at the beginning of each new sample vial. Thereafter, another 6 injections of 2 µl per sample were measured individually as described above, and averages of the last 5 injections were used for further processing. Three standards were measured at the beginning and end of each batch, including a drift standard DI2 (δD: -50.72±0.73 permil, δ18O: -7.63±0.10 permil), and for calibration the laboratory standards GLW (δD: -307.79±0.75 permil, δ18O: -40.02±0.07 permil) and EVAP2 (δD: 9.52±0.65 permil, δ18O: 1.81±0.13 permil). A detailed calibration report is included with the final uploaded data set.

测量期间，降水采用每日至亚日频率采样，采样装置由安装在地面结构上的透明塑料箱（60×40×40 cm）组成。每日采样时段为2020年2月22日至3月24日，于每日固定时间（协调世界时10时）采集样本，并清洁采样箱以备下次采样。此外，在ISLAS宣布的强化观测期（Intense Observation Periods，IOPs）内，ARMS科学家将采样频率提升至亚日级。本次观测期间共开展2次IOPs，累计采集12个样本：IOP1时段为2020年2月27日协调世界时10时至3月2日，IOP2为3月12日至3月14日。箱内固态降水经融化后，转移至8 ml玻璃样品瓶中密封，随后送至挪威卑尔根大学FARLAB实验室进行稳定水同位素分析。降水样本的稳定同位素组成将与其他采样点及蒸发站点的条件关联，以探究水同位素量的守恒规律。2020年2月22日至3月24日期间，于协调世界时10时共采集23个每日样本用于稳定水同位素分析。整个采样期间，降水相态存在高变异性：多数样本为霰/雪（12个），7个为降雨，其余样本则包含霰、雪、降雨或冻雨。降水量在采样箱内的变化范围为<1 mm（2月26日）至140 mm（2月25日）。此外，在2次强化观测期内开展了更高分辨率的采样：IOP1时段为2020年2月27日协调世界时10时至3月2日协调世界时10时，共采集7个样本，均为固态降水；IOP2时段为3月12日协调世界时10时至3月14日协调世界时9时，共采集5个样本（均为霰/雪）。样本处理遵循FARLAB标准测量流程：简要而言，样本被转移至带橡胶/聚四氟乙烯（PTFE）隔垫的1.5 ml玻璃样品瓶（型号548-0907，美国VWR公司）中；自动进样器（型号A0325，Picarro公司）每次进样约2 µl至加热至110℃的高精度蒸发器（型号A0211，美国Picarro公司）；与干燥氮气（H₂O含量<5 ppm）混合后，气体混合物被导入腔衰荡光谱仪（L2140-i，Picarro公司）的测量腔室约7分钟，典型水浓度为20000 ppm。为降低记忆效应，在每个新样品瓶分析开始时，通过2次2 µl进样获取混合比为50000 ppm的蒸汽混合物并测量5分钟，随后按上述方法对每个样本进行6次2 µl进样单独测量，取最后5次进样的平均值用于后续处理。每批样本分析前后均测量3种标准物质：包括漂移标准DI2（δD：-50.72±0.73‰，δ¹⁸O：-7.63±0.10‰），以及用于校准的实验室标准GLW（δD：-307.79±0.75‰，δ¹⁸O：-40.02±0.07‰）和EVAP2（δD：9.52±0.65‰，δ¹⁸O：1.81±0.13‰）。详细校准报告随最终上传数据集一同提供。