Trifluoroacetic acid is a highly persistent and water-soluble compound that is detected with increasing frequency and abundance environmental samples. This compound has an estimated environmental lifetime on the order of tens of thousands of years. This persistence has resulted in its widespread accumulation in different environmental media, leading to detection in global oceans, air, precipitation and human biological samples, including serum and urine. The concentrations measured for TFA are 1-2 orders of magnitude higher than those of other legacy per-and polyfluoroalkyl substances (PFAS) in several environmental media. While TFA is known to form in the atmosphere and deposition to be its primary loss process, the relative contributions of wet and dry deposition pathways require better constraint by observations.

Interest in TFA has intensified following regulatory shifts under the Montreal Protocol, which phased out chlorofluorocarbons (CFCs) and promoted the use of alternative refrigerants. Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) were introduced as transitional replacements but are known precursors of TFA through atmospheric oxidation. More recently, the Kigali Amendment has driven the adoption of hydrofluoroolefins (HFOs), such as HFO-1234yf, which have short atmospheric lifetimes (~12 days) and degrade with near-quantitative yields of TFA. This shift in precursor chemistry is expected to enhance TFA formation and alter its spatial and temporal deposition patterns, even under comparable emission scenarios.

This study investigates the atmospheric deposition of TFA across multiple environments using a combination of total deposition collectors and custom-built automated wet deposition samplers. Sampling was conducted at three sites representing

urban, rural, and tropical regions: York University (Ontario, Canada), Lambton County (Ontario, Canada), and the University of Guyana (South America). Precipitation samples were analyzed via direct injection using ion chromatography-mass spectrometry (IC-MS), enabling sensitive and selective quantification of TFA.

TFA was consistently detected in precipitation across all sites, with datasets spanning one to six years. Observed concentrations indicate both spatial variability and temporal trends, reflecting differences in regional emissions, atmospheric transport, and meteorological conditions. In addition to wet deposition, this study evaluates the contribution of dry deposition to total TFA fluxes. Our findings suggest that dry deposition may represent a significant and previously underappreciated pathway contributing to TFA removal from the atmosphere and entry to surface ecosystems. These results highlight the need to better constrain atmospheric sources and deposition processes of TFA in the context of evolving refrigerant usage and their designed atmospheric degradation.