Trends and variability in tropospheric hydroxyl (OH) radicals influence budgets of many greenhouse gases, air pollutant species, and ozone depleting substances. Estimations of tropospheric OH trends and variability based on budget analysis of methyl chloroform (CH₃CCl₃) and process‐based chemistry transport models often produce conflicting results. Here we use a previously tested transport model to simulate atmospheric CH₃CCl₃ for the period 1985–2018. Based on mismatches between model output and observations, we derive consistent anomalies in the inverse lifetime of CH₃CCl₃ (K_G) using measurements from two independent observational networks (National Oceanic and Atmospheric Administration and Advanced Global Atmospheric Gases Experiment). Our method allows a separation between “physical” (transport, temperature) and “chemical” (i.e., abundance) influences on OH + CH₃CCl₃ reaction rate in the atmosphere. Small increases in K_G due to “physical” influences are mostly driven by increases in the temperature‐dependent reaction between OH and CH₃CCl₃ and resulted in a smoothly varying increase of 0.80% decade⁻¹. Chemical effects on K_G, linked to global changes in OH sources and sinks, show larger year‐to‐year variations (∼2%–3%), and have a negative correlation with the El Niño Southern Oscillation. A significant positive trend in K_G can be derived after 2001, but it persists only through 2015 and only if we assume that CH₃CCl₃ emissions decayed more slowly over time than our best estimate suggests. If global CH₃CCl₃ emissions dropped below 3 Gg year⁻¹ after 2015, recent CH₃CCl₃ measurements indicate that the 2015–2018 loss rate of CH₃CCl₃ due to reaction with OH is comparable to its value 2 decades ago.

中文翻译：

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甲基氯仿继续限制对流层中羟基（OH）的变化

对流层羟基（OH）自由基的趋势和变异性会影响许多温室气体，空气污染物和臭氧消耗物质的预算。根据对甲基氯仿（CH ₃ CCl ₃）的预算分析和基于过程的化学迁移模型估算对流层OH趋势和变异性通常会产生矛盾的结果。在这里，我们使用先前测试的运输模型来模拟1985-2018年期间的大气CH ₃ CCl ₃。基于模型输出和观测值之间的不匹配，我们得出CH ₃ CCl ₃（K _G）使用两个独立的观测网络（国家海洋和大气管理局和高级全球大气实验）进行的测量。我们的方法允许将“物理”（运输，温度）和“化学”（即丰度）对大气中OH + CH ₃ CCl ₃反应速率的影响分开。归因于“物理”影响，K _G的小幅增长主要是由OH和CH ₃ CCl ₃之间的温度相关反应的增加所驱动，并导致0.80％十年^-1的平稳变化。化学对K _G的影响与OH来源和汇的全球变化有关，显示出逐年较大的变化（〜2％–3％），并且与厄尔尼诺南方涛动呈负相关。可以在2001年之后得出K _G的显着正趋势，但是只有当我们假设CH ₃ CCl _3的排放随时间推移衰减的速度比我们的最佳估计所建议的慢时，这种趋势才持续到2015年。如果2015年之后全球CH ₃ CCl ₃排放量降至低于3 Gg - ¹年，则最近的CH ₃ CCl ₃测量表明，2015-2018年CH ₃ CCl _3的损失率 由于与OH的反应，其可比性与20年前的价值相当。