Atmospheric Removal of Trifluoroacetic Acid by Dry and Wet Deposition: A Multiyear Analysis in Toronto

Trifluoroacetic acid (TFA) is a mobile and persistent compound that is widespread in the environment. While TFA forms in the atmosphere and deposition is its primary loss process, the relative contributions of wet and dry deposition require observational constraints. Here, we present a record of TFA in total, wet, and dry deposition in Toronto, Canada, between 2018 and 2024. Samples were collected using custom-built total and automated wet deposition samplers. All total (n = 103) and wet (n = 98) deposition samples contained TFA, with concentrations ranging from 0.07–4.55 μg L–1 and 0.09–3.19 μg L–1, respectively. Seasonal variation showed fluxes peaking in summer months, consistent with atmospheric oxidation of precursors as a major source. Fluxes in 2020 were statistically lower than other years by a factor of 2–5, coinciding with reduced anthropogenic activity during COVID-19 lockdowns. This suggests that TFA sources in Toronto are mainly driven by short-lived precursors. The median dry deposition flux (106 μg m–2 a–1) accounted for 0–94% (median 37%) of the total TFA deposition, higher and more variable than model estimates. These results provide the first field-based quantification of TFA in dry deposition, demonstrating that it is a significant and previously underrepresented removal pathway.