Chlorine atoms play a key role in the oxidative potential of the atmosphere and biogeochemical cycling of selected elements. This study provides a decadal analysis (2010−2019) of chloride ions in PM_2.5 particles in the city of Montreal, where these are most concentrated systematically in the winter (up to 1.6 µg/m³). We also herein present the measurement of photolabile chlorine, which includes chlorine-containing compounds (e.g., Cl₂, HOCl, ClNO₂, ClNO₃, and BrCl) that release chlorine atoms upon interaction with radiation, in urban Montreal, Canada using Cl2-RPGE (Cl2 Reactive Phase Gas Extraction) tubes and quantifying the chlorinated product by GC-MS. Photolabile chlorine in urban Montreal was measured during a discontinuous period primarily in summer 2018 and winter 2019 with a time resolution of 30 min, with concentrations ranging from 3 to 545 ng/m³ expressed as Cl₂. The reported values are considered lower limits, as compounds such as HOCl and ClNO₂ can only be partially converted in the current setup. The largest peak of gaseous photolabile chlorine occurred in the winter, when significant sources of anthropogenic salt are used in snow removal in the city. This coincides with observed chloride ion measurements in airborne particles, implying that anthropogenic salt addition produces photoactive chlorine. The maximum chlorine signal was consistently obtained during the daytime, which is in accordance with the tropospheric radiation profile. Complementary photochemistry laboratory experiments indicated that upon tropospheric radiation (340 ≤ λ ≤ 400 nm; UVA), an increase (20–100%) was observed, confirming the formation of Cl atoms from photolabile chlorine compounds. Thus, this portable technique is adequate for Cl atoms and photolabile chlorine-containing compounds upon photolysis using UVA lamps. High-resolution S/TEM and energy-dispersive X-ray spectroscopy (EDS) were used to evaluate collected particle morphology and composition. The behavior of complementary pollutants (O₃, CO, PM_2.5, and NO_x) was also briefly discussed. We herein discuss the measurement of photolabile halogens within a northern urban metropolitan environment and the impact of anthropogenic sources on chlorine concentrations.

中文翻译：

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寒冷气候蒙特利尔市的人为光不稳定氯

氯原子在大气的氧化势和所选元素的生物地球化学循环中起着关键作用。这项研究提供了蒙特利尔市PM _2.5颗粒中氯离子的年代际分析（2010-2019年），在冬季，这些离子在系统中浓度最高（最高1.6 µg / m ³）。我们在此还介绍了对光不稳定氯的测量，其中包括含氯化合物（例如，Cl ₂，HOCl，ClNO ₂，ClNO ₃（和BrCl）在与辐射相互作用时释放氯原子，该过程在加拿大蒙特利尔市区使用Cl2-RPGE（Cl2反应相气体萃取）管，并通过GC-MS定量氯化产物。蒙特利尔市区的光不稳定氯主要在2018年夏季和2019年冬季的不连续时段内进行测量，时间分辨率为30分钟，浓度范围为3至545 ng / m ^3，表示为Cl ₂。报告的值被认为是下限，因为化合物如HOCl和ClNO ₂在当前设置中只能部分转换。气态光不稳定氯气的最大峰值发生在冬季，当时该城市的除雪过程中使用了大量的人为盐。这与在空气中的颗粒中观察到的氯离子测量值相吻合，这意味着人为添加盐会产生光活性氯。在白天，始终如一地获得最大的氯信号，这与对流层辐射曲线一致。补充的光化学实验室实验表明，在对流层辐射（340≤λ≤400 nm； UVA）下，观察到增加（20-100％），证实了由光不稳定的氯化合物形成的Cl原子。从而，这种便携式技术适用于使用UVA灯进行光解后的Cl原子和对光不稳定的含氯化合物。高分辨率S / TEM和能量色散X射线光谱（EDS）用于评估收集的颗粒形态和组成。补充污染物的行为（O_参照图3，还简要讨论了CO，PM _2.5和NO _x。我们在此讨论北部城市都市环境中对光不稳定卤素的测量以及人为来源对氯浓度的影响。