Understanding the atmospheric transport and fate of fluorinated Persistent Organic Pollutants with global models

全氟羧酸(PFCA)是一种持久性污染物，广泛存在于全球环境中，具有一系列不利影响。长链全氟辛烷烃(碳原子)的生态风险以及人类暴露的途径都得到了很好的证明，这导致了对其生产实施更严格的监管的呼声。短链全氟辛烷烃受到的关注较少，但越来越受到环境的关注。与长链物种一样，在远离工业区的各种偏远地区(如北极)检测到短链全氟辛烷烃，这表明它们是可移动的污染物。超短链全氟辛烷烃包括三氟乙酸(TFA)、全氟丙酸(PFPrA)和全氟丁酸(PFBA)，从大气到地表的沉积是这些污染物的主要生态系统来源(例如Björnsdotter等人，2020年)。在大气中，短链全氟氯烃的二次生产可能是由于初级排放的前体的氧化，包括氟调聚醇(例如Ellis等人，2004年)和为取代现在被《蒙特利尔议定书》禁止的臭氧消耗物质而引入的气体(某些氟氯烃、氢氟碳化合物)。观测证据表明，近几十年来，短链全氟氯烃在地表的沉积显著增加(Pickard等人，2020年；Garnett等人，2022年)，但其全球预算存在很大的不确定性。例如，长期以来一直被认为是TFA的一个重要自然来源现在受到质疑(Joudan等人，2021年)，而从大气中沉积的TFA数量的估计由于以下方面的不确定性而不确定：(1)前体排放的大小、分布和趋势，(2)前体氧化的机制(从而产生全氟丙烷)，以及(3)全球模式中大气输送和其他过程(例如湿/干沉积)的表现。此外，越来越多地使用全球升温潜能值极低的制冷剂(包括氢氟烯烃、氢氟烃)作为TFA和其他全氟辛烷烃的来源，这需要紧急评估，从而使这一专题具有进一步的政策相关性。为了了解短链全氟辛烷烃带来的环境风险，有必要限制其大气预算及其前体的大气预算。为此，该项目的主要目标是：(1)开发UCI三维化学传输模型，以包括主要的短链全氟辛烷化合物及其前体；(2)量化全球/区域短链全氟辛烷化合物的沉积，包括在遥远的极地区域；(3)探索短链全氟氯烃源-受体路径的可变性，以预测大气传输和化学/物理过程中的不确定性(例如对流层氧化剂、干/湿沉积的处理)；以及(4)根据前体排放预测，审查近几十年来短链全氟氯烃沉积的趋势和未来可能的趋势(例如，探索越来越多地使用全球变暖潜能值低的氢氟烃制冷剂的影响)。

Perfluorocarboxylic acids (PFCAs) are persistent pollutants found widely in the global environment where they have a range of adverse effects. Ecological risks from long-chain PFCAs (>7 carbon atoms), along with routes for human exposure, are well documented, leading to calls for more stringent regulation on their production. Short-chain PFCAs have received less attention but are of increasing environmental concern. Like long-chain species, short-chain PFCAs are detected in various remote regions (e.g. the Arctic) vast distances from industrial areas, indicating that they are mobile contaminants. Ultra-short chain PFCAs include trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), and perfluorobutanoic acid (PFBA), with deposition from the atmosphere to the surface a major ecosystem source of these contaminants (e.g. Björnsdotter et al., 2020). In the atmosphere, secondary production of short-chain PFCAs may occur due to the oxidation of primary-emitted precursors, including fluorotelomer alcohols (e.g. Ellis et al., 2004) and gases that were introduced to replace ozone-depleting substances now banned by the Montreal Protocol (certain HCFCs, HFCs). Observational evidence shows deposition of short-chain PFCAs to the surface increased markedly in recent decades (Pickard et al., 2020; Garnett et al., 2022), but there are large uncertainties in their global budget. For example, a long purported significant natural source of TFA is now questioned (Joudan et al., 2021), while estimates of the amount of TFA deposited from the atmosphere are uncertain due to uncertainty in (1) the magnitude, distribution and trends of precursor emissions, (2) the mechanisms of precursor oxidation (and thus PFCA yields), and (3) the representation of atmospheric transport and other processes (e.g. wet/dry deposition) in global models. Moreover, the growing use of ultra-low GWP refrigerants (including hydrofluoroolefins, HFOs) as a source of TFA and other PFCAs requires urgent evaluation, bringing further policy relevance to this topic. To understand environmental risks posed by short-chain PFCAs there is a need to constrain their atmospheric budget and that of their precursors. To that end, key objectives of this project are to (1) develop the UCI 3-D chemical transport model to include major short-chain PFCAs and their precursors; (2) quantify global/regional deposition of short-chain PFCAs, including in remote polar regions; (3) explore variability in short-chain PFCA source-receptor pathways to uncertainties in model atmospheric transport and chemical/physical processes (e.g. tropospheric oxidants, treatment of dry/wet deposition); and (4) examine trends in short-chain PFCA deposition over recent decades and possible future trends based on precursor emission projections (e.g. explore the impact of the growing use of low-GWP HFO refrigerants).