Bromine and chlorine chemistry in the Arctic atmospheric boundary layer has significant impacts on tropospheric ozone depletion and the fates of atmospheric pollutants, including mercury and hydrocarbons. Bromine chloride (BrCl) produces bromine and chlorine radicals upon photolysis and links these two halogen cycles. However, because of the limited number of BrCl measurements, the relative importance of its production and removal pathways are uncertain. Here we report BrCl observations near Utqiaġvik, AK, during March–May 2016 using chemical ionization mass spectrometry as part of the Photochemical Halogen and Ozone Experiment: Mass Exchange in the Lower Troposphere (PHOXMELT). Two distinct BrCl diel regimes were identified, with daytime BrCl primarily observed in March and nighttime BrCl observed in April and May, demonstrating a dependence on photochemistry. The dominant BrCl production mechanisms for these regimes were explored using a zero-dimensional numerical model constrained to a suite of halogen measurements. Multiphase reactions on the snowpack surface, mainly via Cl₂ + Br^–(aq) and HOBr + Cl^–(aq), are predicted to be the largest contributors to near-surface BrCl production. Average net snowpack fluxes of 1.9 × 10⁸ and 2.2 × 10⁸ BrCl molecules cm^–2 s^–1 for two case periods in March and May are needed to explain the observations. The findings in this work highlight coupled bromine and chlorine chemistry and important halogen activation pathways in the springtime Arctic boundary layer.

中文翻译：

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沿海北极地区的氯化溴：狄尔图案和产生机理

北极大气边界层中的溴和氯化学对对流层臭氧消耗和包括汞和碳氢化合物在内的大气污染物的命运具有重大影响。氯化溴（BrCl）在光解时会产生溴和氯自由基，并将这两个卤素循环联系在一起。但是，由于BrCl测量的数量有限，因此不确定其生产和去除途径的相对重要性。在这里，我们报告了2016年3月至5月使用化学电离质谱作为光化学卤素和臭氧实验：低层对流层质量交换（PHOXMELT）的一部分，在阿肯色州乌特恰维克附近的BrCl观测结果。确定了两种不同的BrCl diel方案，白天的BrCl主要在3月观察到，而夜间的BrCl在4月和5月观察到，证明了对光化学的依赖性。使用约束于一组卤素测量值的零维数值模型探索了这些方案的主要BrCl产生机理。积雪表面上的多相反应，主要是通过Cl₂ +溴^-（aq）和次溴酸+氯^- （水溶液），被预测为最大贡献者近表面氯化溴生产。在三月和五月的两个案例期间，需要平均净积雪通量为1.9×10 ⁸和2.2×10 ⁸ BrCl分子cm ^–2 s ^–1，以解释观测结果。这项工作的发现突出了春季北极边界层中的溴和氯化学耦合以及重要的卤素活化途径。