Airborne trifluoroacetic acid and its fraction from the degradation of HFC-134a in Beijing, China

Evidences for the influence from key chemical structures of per- and polyfluoroalkyl substances on their environmental behaviors

This study carried out the atmospheric and precipitation observation in Beijing for nearly one year, and firstly simultaneously observed the pollution characteristics of PFASs and their main isomers, focusing on their gas-particle partitioning mechanism and dry and wet deposition characteristics. After deducting PFASs in the aqueous phase of particulate matter, the gas-particle partitioning coefficients (-7.04 to -5.49) were about 3-4 units smaller than before (-2.77 to -1.51), and all were smaller than 0, which indicated that each PFAS and isomer were more distributed in the gas phase. Dry deposition was dominant in the atmospheric deposition of each PFAS and isomer with relative contribution of 66 ± 17%, but the relative contribution of dry deposition was significantly different. It was found that the gas-particle partitioning coefficient can be influenced by key chemical structures such as carbon chain length, functional group type, and isomer structure. Furthermore, the gas-particle partitioning can influence the dry and wet deposition of PFASs. Specifically, PFASs with longer carbon chains, carboxylic acid functional group (compared to sulfonic acid functional group) or PFOA branched chain structures had larger gas-particle partitioning coefficients and can be more distributed in the hydrophobic phase of particulate matter, and their relative contributions of dry deposition were smaller.

New insights into the mechanism and kinetics of the addition reaction of unsaturated Criegee intermediates to CF3COOH and tropospheric implications

In this work, we have investigated the mechanism, thermochemistry and kinetics of the reaction of syn-cis-CH2RzCRyCO+O- (where Rz, Ry = H, CH3-) unsaturated Criegee intermediates (CIs) with CF3COOH using quantum chemical methods. The rate coefficients for the barrierless reactions were calculated using variable reaction coordinate variational transition state theory (VRC-VTST). For the syn-cis-CH2RzCRyCO+O- conformation in which conjugated CC and CO double bonds are aligned with each other, we propose a new pathway for the unidirectional addition of an OC-OH molecule (CF3COOH) to the CC double bond of syn-cis-CH2RzCRyCO+O-. The rate coefficient for the 1,4-CC addition reaction at 298 K is ∼10-10 to 10-11 cm3 s-1, resulting in the formation of CF3C(O)OCH2CRzRyCOOH trifluoroacetate alkyl allyl hydroperoxide (TFAAAH) as a new transitory adduct. It can act as a precursor for the formation of secondary organic aerosols (SOAs). This novel TFAAAH hydroperoxide was identified through a detailed quantum chemical study of the 1,4-addition mechanism and will provide new insights into the significance of the 1,4-addition reaction of unsaturated Cls with trace tropospheric gases on -CRzCH2 vinyl carbon atoms.

The wide presence of fluorinated compounds in common chemical products and the environment: a review

The C-F bonds, due to their many unique features, have been incorporated into numerous compounds in countless products and applications. These fluorinated compounds eventually are disposed of and released into the environment through different pathways. In this review, we analyzed the occurrence of these fluorinated compounds in seven types of products (i.e., refrigerants/propellants, aqueous film-forming foam, cosmetics, food packaging, agrochemicals, pharmaceuticals, coating materials) and discussed their fate in the environment. This is followed by describing the quantity of fluorinated compounds from each source based on available data. Total on- and off-site disposal or other releases of 536 fluorinated compounds in 2021 were analyzed using the data sourced from the U.S. EPA Toxics Release Inventory (TRI). Among the chemicals examined, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) were the primary contributors in terms of total mass. Upon examining the seven sources of fluorinated compounds, it became evident that additional contributors are also responsible for the presence of organofluorine compounds in the environment. Although various toxic degradation products of fluorinated compounds could form in the environment, trifluoroacetic acid (TFA) was specifically highlighted in this review given the fact that it is a common dead-end degradation product of > 1 million chemicals. This paper ended with a discussion of several questions raised from this study. The path forward was elaborated as well for the purpose of protecting the environment and human health.

Projections of National-Gridded Emissions of Hydrofluoroolefins (HFOs) in China

Hydrofluoroolefins (HFOs) are being used as substitutes for potent greenhouse gas hydrofluorocarbons (HFCs). However, the use and environmental impacts of HFOs are of great concern due to the rapid degradation of HFOs to produce persistent and phytotoxic trifluoroacetic acid (TFA). Here, we provide a comprehensive projection of HFO emissions in China during 2024-2060 for the first time. Under the Kigali Amendment to the Montreal Protocol, China's HFO emissions are estimated to increase from 1.7 (1.3-2.3) to 148.8 (111.4-185.4) kt in 2024-2060 with cumulative emissions of 2.8 (2.0-3.5) Gt, and cumulative reduced HFCs emissions are evaluated to be 5.4 Gt CO2-equivalent. High HFO emissions would be distributed mainly in the North China Plain and the eastern and coastal areas. HFO-1234yf (2,3,3,3-tetrafluoropropene) contributes most of HFO emissions with a cumulative emission of 1.7 Gt in 2024-2060, while the cumulative increment of TFA deposition from HFO-1234yf emissions would reach 0.4-1.0 Gt. The long-term national-gridded HFO emission inventories can provide scientific support for evaluating the environmental risks of HFOs and developing HFC phase-out pathways for addressing climate change.

Electronic-waste-associated pollution of per- and polyfluoroalkyl substances: Environmental occurrence and human exposure

Occupational exposure to per- and polyfluoroalkyl substances (PFASs) is of serious concern because their adverse health effects. Nevertheless, knowledge regarding contamination in e-waste dismantling regions is rather scarce. We therefore analysed seven neutral PFASs (n-PFASs) and forty ionized PFASs (i-PFASs) in dust and hand wipes collected from an e-waste dismantling plant and homes. Both dust (1370 ng/g) and workers' hand wipe (1100 ng/m²) in e-waste dismantling workshops contained significantly higher median levels of ∑PFASs than those from homes (684 ng/g and 444 ng/m²) (p < 0.01). ∑PFAS concentrations in dust and on workers' hand wipes from workshops were significantly higher than those from storage area. 8:2 fluorotelomer alcohol was the dominant n-PFAS in workshop dust (70.7%) and on worker's hand wipes (46.6%). Perfluoroalkyl carboxylic acids (C2 -C3) were the significant components (based on concentration) of i-PFASs in dust (57.9%) and on hand wipes (89.6%). A significant positive correlation (p < 0.001) of ∑PFAS concentrations between workshop dust and workers' hand wipes was observed, indicating that they come from common sources. Compared to dust ingestion, hand-to-mouth contact was highlighted as a vital exposure route, accounting for 68.8% for workers and 72.2% for residential population, respectively, of the sum of two exposure doses.

Exploring controls on perfluorocarboxylic acid (PFCA) gas-particle partitioning using a model with observational constraints

The atmospheric fate of perfluorocarboxylic acids (PFCAs) has attracted much attention in recent decades due to the role of the atmosphere in global transport of these persistent chemicals. There is a gap in our understanding of gas-particle partitioning, limited by availability of reliable atmospheric measurements, partitioning properties, and models of gas-particle interactions. The gas-particle equilibrium phase partitioning of C2-C16 PFCAs in the atmosphere were modeled here by taking account of both deprotonation and phase partitioning equilibria among air, aerosol liquid water, and particulate water-insoluble organic matter using a range of available PFCA partitioning properties. We systematically varied water and organic matter content to simulate the full range of atmospheric conditions. Except in severe organic matter pollution episodes, shorter-chain PFCAs are predicted to mainly partition between air and aqueous phase, while for PFCAs with carbon chains longer than 12, organic matter is more likely to be the dominant particle phase reservoir. The model framework underestimated the particle fraction of C2-C8 PFCAs compared with several ambient observations, with larger discrepancies observed for longer-chain PFCAs. The discrepancy could result from externally mixed dust components, non-ideality of aerosol liquid water, surfactant descriptions at phase boundaries, and missed interactions between organic matter and charged PFCA molecules. Reliable measurements of ambient PFCAs with high time resolution and the measurement of uptake parameters by particle-relevant components will be beneficial to more reliable environmental fate modeling of ambient PFCAs.

Fluorine mass balance analysis and per- and polyfluoroalkyl substances in the atmosphere

Given that only a small number of per- and polyfluoroalkyl substances (PFAS) are routinely monitored, levels of PFAS in the atmosphere may be underestimated. A protocol including analyses of target PFAS (n = 50), water-soluble fluoride, and total fluorine has been proposed and applied to atmospheric samples. The whole method recovery (including extraction recovery and sampling efficiency) of 90-110% were obtained for the majority of compounds (48/50) with low deviations between replicates (< 20%). Fluorotelomer alcohols were the most prevalent PFAS in the indoor air, while the outdoor air was dominated by the ultrashort-chain ionic PFAS (e.g., trifluoroacetic acid and perfluoropropanoic acid). Concentrations of organofluorine (OF) compounds calculated from the fluorine mass balance ranged from 1.74 ng F/m³ to 14.3 ng F/m³ and from 52.0 ng F/m³ to 1100 ng F/m³ in the particulate and gaseous phases, respectively, whereas only a minor proportion (around 1%) could be explained by target PFAS. In indoor air, OF compounds were observed in relatively high levels and with a shift to the fine particles (PM_<1) . Our results reveal a large proportion of unidentified OF signatures in the atmosphere and suggest the need to use multiple approaches to improve our understanding of airborne fluorinated substances.

Increases in Trifluoroacetate Concentrations in Surface Waters over Two Decades

Trifluoroacetate (TFA) is a persistent perfluorinated alkanoic acid anion that has many anthropogenic sources, with fluorocarbon refrigerants being a major one. After an initial burst of research in the late 1990s and early 2000s, research on this ubiquitous pollutant declined as atmospheric emissions of the precursor compounds grew rapidly. Thus, there is little contemporaneous information about the concentrations of TFA in the environment and how they have changed over time. This research determined the change in TFA concentrations in streams by resampling a transect that was originally sampled in 1998. The transect was designed to determine the regional distribution of TFA both upwind and downwind of major metropolitan areas in Northern California as well as a set of globally remote sites in Alaska. The results showed that TFA concentrations increased by an average of 6-fold over the intervening 23 years, which resulted in a median concentration of 180 ng/L (range 21.3-2790). The highest concentrations were found in streams immediately downwind of the San Francisco Bay Area, while substantially lower concentrations were found in the upwind, regionally remote, and globally remote sites. The C₃ to C₅ perfluorinated alkanoic acids were also investigated, but they were rarely detected with this methodology.

Insufficient evidence for the existence of natural trifluoroacetic acid

Trifluoroacetic acid (TFA) is a persistent and mobile pollutant that is present ubiquitously in the environment. As a result of a few studies reporting its presence in pre-industrial samples and a purported unaccounted source, TFA is often claimed to exist naturally. Here, we examine the evidence for natural TFA by: (i) critically evaluating measurements of TFA in pre-industrial samples; (ii) examining the likelihood of TFA formation by hypothesized mechanisms; (iii) exploring other potential TFA sources to the deep ocean; and (iv) examining global budgets of TFA. We conclude that the presence of TFA in the deep ocean and lack of closed TFA budget is not sufficient evidence that TFA occurs naturally, especially without a reasonable mechanism of formation. We argue the paradigm of natural TFA should no longer be carried forward.

Residue analytical method for the determination of trifluoroacetic acid and difluoroacetic acid in plant matrices by capillary electrophoresis tandem mass spectrometry (CE-MS/MS)

In the past years, the technology for trace residue analysis of plant protection compounds in plant and animal matrices, soil, and water has gradually changed to meet changing regulatory demands. Generally, from the '70s to the '90s of the last century, the active compounds and only a few major metabolites had to be determined in a typical "residue definition". Step by step and within the framework of product safety assessments of the enforcement of residues in dietary matrices and in the environment, further metabolites have come into the authorities focus. Many active substances were formerly determined via gas chromatography (GC) based detection techniques. The introduction of liquid chromatography tandem mass spectrometry (LC-MS/MS) technology in the '90s and the acceptance of this technique, by official bodies at the end of the '90s, has led to a major change for residue analytical laboratories all over the world. Most of the medium to non-polar active compounds as well as many of the more polar metabolites can be detected with this technique, and today LC-MS/MS is the "workhorse" in many residue analytical laboratories in the industry as well as official enforcement labs responsible for analyzing registration-related field studies. With the demand to analyze further breakdown products, more and more polar compounds, or even (permanently) charged target compounds, have now come into the focus of the registration authorities. This now brings standard LC-based techniques to their limits and requires the application of approaches such as hydrophilic interaction chromatography (HILIC) MS/MS or ion chromatography, however these techniques often incur related uncertainties and problems with matrix samples. The aim of this study was to develop a new CE-MS/MS-based approach to reduce the impact of matrix on the separation and detection of trifluoroacetic acid (TFA) and difluoroacetic acid (DFA) in agrochemical field trials. This project used 7 representative examples of fruit, grain and vegetables which had undergone homogenization and extraction with acetonitrile water and filtration before CE-MS/MS analysis. The CE-MS/MS developed reached the limit of quantitation (LOQ) requirement of current legislation for both TFA and DFA (0.01 mg/kg) in all 7 matrices tested. The mean relative standard deviation (RSD) obtained from the repeat analysis of control field trail samples in all matrices, for both TFA and DFA, was less than 10% meeting GLP guidelines. When compared with LC-MS/MS, using on column loading amounts, the CE-MS/MS was 17 - 43 times more sensitive than a standard method and less matrix effects were observed. The developed method was validated under GLP conditions to provide a GLP-validated residue analytical method for the charged metabolites TFA and DFA in matrix samples from GLP field residue trials.

Uptake and accumulation of per- and polyfluoroalkyl substances in plants

Per- and polyfluoroalkyl substances (PFASs) are a class of persistent organic contaminants that are ubiquitous in the environment and have been found to be accumulated in agricultural products. Consumption of PFAS-contaminated agricultural products represents a feasible pathway for the trophic transfer of these toxic chemicals along food chains/webs, leading to risks associated with human and animal health. Recently, studies on plant uptake and accumulation of PFASs have rapidly increased; consequently, a review to summarize the current knowledge and highlight future research is needed. Analysis of the publications indicates that a large variety of plant species can take up PFASs from the environment. Vegetables and grains are the most commonly investigated crops, with perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) as the most studied PFASs. The potential sources of PFASs for plant uptake include industrial emissions, irrigation with contaminated water, land application of biosolids, leachates from landfill sites, and pesticide application. Root uptake is the predominant pathway for the accumulation of PFASs in agricultural crops, and uptake by plant aboveground portions from the ambient atmosphere could play a minor role in the overall PFAS accumulation. PFAS uptake by plants is influenced by physicochemical properties of compounds (e.g., perfluorocarbon chain length, head group functionality, water solubility, and volatility), plant physiology (e.g., transpiration rate, lipid and protein content), and abiotic factors (e.g., soil organic matters, pH, salinity, and temperature). Based on literature analysis, the current knowledge gaps are identified, and future research prospects are suggested.

Review on perfluoroalkyl and polyfluoroalkyl substances (PFASs) in the Chinese atmospheric environment

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been manufactured and used for over 50 years, and now are worldwide distributed in the environment. The atmospheric environment is the main compartment for PFASs to be transported and transformed, and relevant research has highlighted the global occurrence and impacts of atmospheric PFASs in ecosystems and human health. With the phasing-out and restriction of eight‑carbon chain-length (C8) PFASs in developed countries, China has become the largest producer of C8 PFASs since 2004. Subsequently, a number of studies on PFASs in the Chinese atmospheric environment have been conducted in the recent decade. This review documented twenty-eight studies on PFASs in Chinese outdoor air published to date. Methods of sampling, extraction, cleanup, and instrumental analysis were summarized for both ionic and neutral PFASs. Levels, compositions, and spatial distribution of PFASs from different areas in China (i.e. source, urban, and remote regions, and north versus south China) were compared and discussed. Leaves and tree barks were proposed as effective bioindicators to reflect the contamination status of atmospheric PFASs. Special attention can be given to non-target screening for future research directions.

Trifluoroacetate in Precipitation: Deriving a Benchmark Data Set

Although precipitation is considered to be the most important diffuse source of trifluoroacetate (TFA) to the nonmarine environment, information regarding the wet deposition of TFA as well as general data on the spatial and temporal variations in TFA concentration in precipitation is scarce. This is the first study to provide a comprehensive overview of the occurrence of TFA in precipitation by a systematic and nation-wide field monitoring campaign. In total, 1187 precipitation samples, which were collected over the course of 12 consecutive months at eight locations across Germany, were analyzed. The median, the estimated average, and the precipitation-weighted average TFA concentration of all analyzed wet deposition samples were 0.210, 0.703, and 0.335 μg/L, respectively. For Germany, an annual wet deposition flux of 190 μg/m² or approximately 68 t was calculated for the sampling period from February 2018 to January 2019. The campaign revealed a pronounced seasonality of the TFA concentration and wet deposition flux of collected samples. Correlation analysis suggested an enhanced transformation of TFA precursors in the troposphere in the summertime due to higher concentrations of photochemically generated oxidants such as hydroxyl radicals, ultimately leading to an enhanced atmospheric deposition of TFA during summer.

Fluorochemicals biodegradation as a potential source of trifluoroacetic acid (TFA) to the environment

The anthropogenic release of trifluoroacetic acid (TFA) into the environmental media is not limited to photochemical oxidation of CFC alternatives and industrial emissions. Biological degradation of some fluorochemicals is expected to be a potential TFA source. For the first time, we assess if the potential precursors [6:2 fluorotelomer alcohol (6:2 FTOH), 4:2 fluorotelomer alcohol (4:2 FTOH), acrinathrin, trifluralin, and 2-(trifluoromethyl)acrylic acid (TFMAA)] can be biologically degraded to TFA. Results show that 6:2 FTOH was terminally transformed to 5:3 polyfluorinated acid (5:3 FTCA; 12.5 mol%), perfluorohexanoic acid (PFHxA; 2.0 mol%), perfluoropentanoic acid (PFPeA; 1.6 mol%), perfluorobutyric acid (PFBA; 1.7 mol%), and TFA (2.3 mol%) by day 32 in the landfill soil microbial culture system. 4:2 FTOH could remove multiple -CF₂ groups by microorganisms and produce PFPeA (2.6 mol%), PFBA (17.4 mol%), TFA (7.8 mol%). We also quantified the degradation products of TFMAA as PFBA (1.3 mol%) and TFA (6.3 mol%). Furthermore, we basically analyzed the biodegradation contribution of short-chain FTOH as raw material residuals in commercial products to the TFA burden in the environmental media. We estimate global emission of 3.9-47.3 tonnes of TFA in the period from 1961 to 2019, and project 3.8-46.4 tonnes to be emitted from 2020 to 2040 via the pathway of 4:2 and 6:2 FTOH biodegradation (0.6-7.1 and 0.6-7.0 tonnes in China, respectively). Direct evidence of the experiments indicates that biodegradation of fluorochemicals is an overlooked source of TFA and there are still some unspecified mechanisms of TFA production pathways.

Phototransformation of perfluorooctane sulfonamide on natural clay minerals: A likely source of short chain perfluorocarboxylic acids

In this study, a new phototransformation pathway for perfluorooctane sulfonamide (FOSA) and underlying degradation mechanisms are described. Phototransformation of FOSA in a natural clay mineral (montmorillonite) suspension was compared to that in an aqueous solution. Results showed that the presence of montmorillonite can significantly promote the transformation of FOSA to perfluocarboxylic acids (increasing rate). The phototransformation reaction was found to be initiated by the activation of adsorbed oxygen molecules on the surface of montmorillonite, which generate superoxide anion and hydroxyl radicals. Hydroxyl radicals can then attack FOSA adsorbed onto the surface of montmorillonite, promoting the transformation process. In this reaction, clay minerals played a dual role: providing hydroxyl radicals and concentrating FOSA on their surfaces. This helped to promote the contact and reaction between FOSA and hydroxyl radicals. This study provides the first evidence that heterogeneous oxidation of FOSA at the surface of natural clay minerals may act as an important source of perfluocarboxylic acids (PFCAs), especially short chain PFCAs (i.e. trifluoroacetic acid, TFA).

Challenges in the analytical determination of ultra-short-chain perfluoroalkyl acids and implications for environmental and human health

Ultra-short-chain perfluoroalkyl acids have recently gained attention due to increasing environmental concentrations being observed. The most well-known ultra-short-chain perfluoroalkyl acid is trifluoroacetic acid (TFA) which has been studied since the 1990s. Potential sources and the fate of ultra-short-chain perfluoroalkyl acids other than TFA are not well studied and data reporting their environmental occurrence is scarce. The analytical determination of ultra-short-chain perfluoroalkyl acids is challenging due to their high polarity resulting in low retention using reversed-phase liquid chromatography. Furthermore, recent studies have reported varying extraction recoveries in water samples depending on the water matrix and different methods have been suggested to increase the extraction recovery. The present review gives an overview of the currently used analytical methods and summarizes the findings regarding potential analytical challenges. In addition, the current state of knowledge regarding TFA and other ultra-short-chain perfluoroalkyl acids, namely perfluoropropanoic acid, trifluoromethane sulfonic acid, perfluoroethane sulfonic acid, and perfluoropropane sulfonic acid‚ are reviewed. Both known and potential sources as well as environmental concentrations are summarized and discussed together with their fate and the environmental and human implications.

Distribution characteristics of trifluoroacetic acid in the environments surrounding fluorochemical production plants in Jinan, China

Trifluoroacetic acid (TFA) is a ubiquitous and extremely stable contaminant in the ambient environment and may be discharged during fluorochemical production processes. However, the impacts of fluorochemical production on surrounding areas have seldom been evaluated. We focused on Jinan, the capital of Shandong Province, China, and measured TFA levels in water, soil, and air samples. Our results showed that the average TFA concentrations in flowing water bodies were lower than those in landscape water bodies. The average TFA concentrations in soils were significantly higher than the background concentration. As for atmospheric TFA levels, the mean concentrations in the gas phase were higher than those in the particle phase, and average daytime levels were slightly higher than nighttime levels. In addition, the quotient method was used to assess the ecological risk of TFA in water in Jinan. The ratio of pollutant environmental concentration to predicted no-effect concentration (PEC/PNEC) for TFA was greater than 1, indicating that TFA does potentially damage the aquatic ecosystem of Jinan. Our findings suggest that TFA pollution around fluoride production plants is a serious problem and that actions are required to avoid exacerbating the local ecological and environmental risks of TFA.

Atmospheric perfluoroalkyl acid occurrence and isomer profiles in Beijing, China

The airborne occurrence, isomer profiles, and phase distribution of perfluoroalkyl acids (PFAAs), including perfluoroalkyl carboxylates (PFCAs) and sulfonates (PFSAs), have received little scientific attention to date. Here we collected gaseous and particulate phase (PM_2.5) samples in China, between June and November 2013, using alkalized annular denuders and downstream filters toavoid sampling artefacts associated with traditional air sampling. We analysed the concentrations of 18 linear PFAAs and the branched isomers of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS). Concentrations of total PFAAs were dominated by PFCAs, with a range of 6.6-610 pg/m³ in the gaseous phase and 2.3-290 pg/m³ in the particulate phase. Concentrations of total PFCAs were higher in summer than winter in both phases. Branched PFOA isomers accounted for 10-22% of total PFOA in the gaseous phase and 13-24% in the particulate phase, which is close to, but slightly lower than, their abundance in the commercial PFOA mixtures manufactured using the electrochemical fluorination (ECF) process. In contract, branched PFOS isomers accounted for 26-63% of total PFOS in the gaseous phase and 39-77% in the particulate phase, which is much higher than their abundance in commercial PFOS mixtures manufactured by ECF. Most PFCAs had mean particle-associated fractions (Φ) higher than 0.5. PFHxS had a much higher mean Φ (0.65) than linear PFOS (0.31). We hypothesise that PFAAs observed in Beijing air may originate from the local water bodies through processes such as aerosol generation, although transformation of precursors also contribute.

The contribution of fluoropolymer thermolysis to trifluoroacetic acid (TFA) in environmental media

The source of trifluoroacetic acid (TFA) has long been a controversial issue. Fluoropolymer thermolysis is expected to be a potential anthropogenic source except for CFC alternatives. However, its TFA yield and contributions have rarely been reported more recently. In this study, we investigated the thermal properties of three kinds of fluoropolymers, including poly (vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP), poly (vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) and poly (tetrafluoroethylene) (PTFE). A laboratory simulation experiment was then performed to analyze the TFA levels in the thermolysis products and hence to examine the TFA yields of these fluoropolymers. Thermolysis of these fluoropolymers occurred in the temperature ranges from ∼400 °C to ∼650 °C, with the peak weight loss rate at around 550-600 °C. TFA could be produced through fluoropolymer thermolysis when being heated to 500 °C and above. Average TFA yields of PTFE, PVDF-HFP and PVDF-CTFE were 1.2%, 0.9% and 0.3%, respectively. Furthermore, the contribution of fluoropolymer thermolysis and CFC alternatives to rainwater TFA in Beijing, China was evaluated by using a Two-Box model. The degradation of fluoropolymers and HCFCs/HFCs could explain 37.9-43.4 ng L^-1 rainwater TFA in Beijing in 2014. The thermolysis of fluoropolymers contributed 0.6-6.1 ng L^-1 of rainwater TFA, accounting for 1.6-14.0% of the TFA burden from all the precursors which were considered here.

Per- and polyfluoroalkyl substances (PFASs) in precipitation from mainland China: Contributions of unknown precursors and short-chain (C2C3) perfluoroalkyl carboxylic acids

A nationwide survey was conducted on per- and polyfluoroalkyl substances (PFASs) in precipitation across mainland China. Twenty-two PFASs, including precursors to perfluoroalkyl acids (pre-PFAAs), were investigated in thirty-nine precipitation samples collected from twenty-eight cities. Trifluoroacetate (TFA), perfluorooctanoic acid, and perfluorooctane sulfonic acid (PFOS) were ubiquitous in precipitation. TFA displayed the highest concentrations (8.8-1.8 × 10³ ng/L), which were particularly elevated in coastal cities. 6:2 chlorinated polyfluorinated ether sulfonic acid, an alternative to PFOS, was detected for the first time in precipitation at a frequency of 43%. Polyfluoroalkyl phosphoric acid diesters and 6:2 fluorotelomer sulfonic acid were also occasionally detected. PFAS fluxes in the northeastern area (C4C12; 2.0 × 10²-3.4 × 10³ ng/m²/d) with major PFAS manufacturing facilities were higher than those in the southwestern area (63-1.7 × 10³ ng/m²/d). Using total oxidizable precursor (TOP) assay, the occurrence of unknown pre-PFAAs was for the first time uncovered in precipitation with maximum estimated fluxes of C6 and C8 pre-PFAAs at 3.1 × 10³ and 4.3 × 10³ ng/m²/d, respectively. The relative contribution of ultrashort-chain PFCAs (C2C3) ranged from 22% to 91% of ∑PFASs, while unknown pre-PFAAs accounted for 6%-56% of the total molar concentrations of PFASs. This bears critical concerns on underestimation of PFAS mass load from precipitation to surface environment ascribed to monitoring data solely on known PFASs. Unknown precursors of PFAAs in the atmosphere are yet to be identified for their chemical structures and relevant environmental risks as well.

Distribution of trifluoroacetic acid in gas and particulate phases in Beijing from 2013 to 2016

Trifluoroacetic acid (TFA) was measured at an urban site in Beijing from April 2013 to April 2016 and examined its characteristics and particle/gas distributions. The average monthly atmospheric TFA concentration fluctuated significantly and presented marked seasonal variations. The concentration levels of gas-phase TFA were significantly higher in spring and summer than in fall and winter. The PM_2.5 mass concentration and ambient temperature were important factors affecting the concentration of particulate-phase TFA. Hence, at higher PM_2.5 concentrations and lower temperatures, atmospheric TFA tended to be enriched in particulate matter. Our findings suggest that the percentage of gas-phase TFA in Beijing is higher than that in the steady state; thus, gas-phase TFA can still be transformed to the particulate phase and increase the contribution of TFA to haze formation.

Multimedia Distribution and Transfer of Per- and Polyfluoroalkyl Substances (PFASs) Surrounding Two Fluorochemical Manufacturing Facilities in Fuxin, China

Industrial facilities can be point sources of per- and polyfluoroalkyl substances (PFASs) emission to the surrounding environment. In this study, 25 neutral and ionizable PFASs were analyzed in 94 multimedia samples including air, rain, outdoor settled dust, soil, plant leaves, river water, surface sediment, and shallow groundwater from two fluorochemical manufacturing parks (FMPs) in Fuxin, China, to elucidate the multimedia distribution and transfer pattern of PFASs from a point source. The concentrations of individual PFASs in air, outdoor settled dust, and surface river water decreased exponentially as the distance increases from the FMPs, whereas the concentrations of short-chain (C2-C4) perfluoroalkyl carboxylic acids (PFCAs) remained high (3000 ng/L) in the surface water 38 km away. At FMPs, air concentrations of fluorotelomer alcohols and iodides were found dominant with levels of up to 7900 pg/m³ and 920 pg/m³, respectively. Trifluoroacetic acid was directly released from FMPs and occurred in all the environmental matrices at levels 1-2 orders of magnitude higher than other PFCAs. Higher air-water concentration ratios of short-chain PFCAs (C2-C4) suggested their transfer tendency from air to water. Both short-chain (C2) and long-chain (>C6) PFCAs have greater sediment-water distribution coefficients and deposit dust-air coefficients, which have great influences on the long-range transport potential of different analogues.

Impacts of the Degradation of 2,3,3,3-Tetrafluoropropene into Trifluoroacetic Acid from Its Application in Automobile Air Conditioners in China, the United States, and Europe

HFO-1234yf (2,3,3,3-tetrafluoropropene) was proposed as an automobile air conditioner (MAC) refrigerant worldwide. However, its atmospheric degradation product is the highly soluble and phytotoxic trifluoroacetic acid (TFA), which persists in aquatic environments. We used a global three-dimensional chemical transport model to assess the potential environmental effects resulting from complete future conversion of the refrigerant in all MAC to HFO-1234yf in China, the United States, and Europe. The annual mean atmospheric concentrations of HFO-1234yf were 2.62, 2.20, and 2.73 pptv, and the mean deposition rates of TFA were 0.96, 0.45, and 0.52 kg km^-2 yr^-1, in three regions. The regional TFA deposition sources mainly came from emissions within the same region. The annual TFA deposition in the North Pole region was lower than the global average and mainly originated from European emissions. A potential doubling in the future HFO-1234yf emissions in China mainly affected the local TFA depositions. The TFA concentrations in rainwater were strongly affected by the regional precipitation rates. North Africa and the Middle East, regions with scant rainfall, had extremely high TFA concentrations. The rainwater concentrations of TFA during individual rain events can exceed the level considered to be safe, indicating substantial potential regional risks from future HFO-1234yf use.

Occurrence and Phase Distribution of Neutral and Ionizable Per- and Polyfluoroalkyl Substances (PFASs) in the Atmosphere and Plant Leaves around Landfills: A Case Study in Tianjin, China

A total of 23 per- and polyfluoroalkyl substances (PFASs) were investigated in the air, dry deposition, and plant leaves at two different landfills and one suburban reference site in Tianjin, China. The potential of landfills as sources of PFASs to the atmosphere and the phase distribution therein were evaluated. The maximum concentrations of ∑PFASs in the two landfills were up to 9.5 ng/m³ in the air, 4.1 μg/g in dry deposition, and 48 μg/g lipid in leaves with trifluoroacetic acid and perfluoropropionic acid being dominant (71%-94%). Spatially, the distribution trend of ionizable and neutral PFASs in all three kinds of media consistently showed the central landfill > the downwind > the upwind > the reference sites, indicating that landfills are important sources to PFASs in the environment. Plant leaves were found effective in uptake of a variety of airborne PFASs including polyfluoroalkyl phosphoric acid diesters, thus capable of acting as a passive air sampling approach for air monitoring.

Dynamic and thermodynamic mechanisms of TFA adsorption by particulate matter

Trifluoroacetic acid (TFA) in the atmosphere is produced by degradation of hydrochlorofluorocarbons and hydrofluorocarbons. In recent years, TFA has attracted global attention because of increased environmental concentrations, biological toxicity and accumulation in aqueous environments. This study focused on the mechanisms underlying the adsorption of TFA by particulate matter to identify the appropriate descriptive model for this process and thus improve estimation of TFA adsorption in future environmental monitoring. Onsite gas and particle phase sampling in Beijing, China, and subsequent measurement of TFA concentrations indicated that the TFA concentration in the gas phase (1396 ± 225 pg m^-3) was much higher than that in the particle phase (62 ± 8 pg m^-3) and that monthly concentrations varied seasonally with temperature. Based on the field results and analysis, an adsorption experiment of TFA on soot was then conducted at three different temperatures (293, 303, and 313 K) to provide parameters for kinetic and thermodynamic modelling. The proportion of atmospheric TFA concentration in the gas phase increased with temperature, indicating that temperature affected the phase distribution of TFA. The subsequent kinetic and thermodynamic modelling showed that the adsorption of TFA by soot could be described well by the Bangham kinetic model. The adsorption was controlled by diffusion, and the key mechanism was physical adsorption. The adsorption behavior can be well described by the Langmuir isotherm model. The calculated thermodynamic parameters ΔG° (-2.34, -1.25, and -0.15 kJ mol^-1 at 293, 303, and 313 K, respectively), ΔH° (-34.34 kJ mol^-1), and ΔS° (-109.22 J mol^-1 K^-1) for TFA adsorption by soot were negative, indicating that adsorption was a spontaneous, exothermic process.