The role of trifluoroacetic acid in new particle formation from methanesulfonic acid-methylamine.

The contribution of methanesulfonic acid (MSA) to new particle formation (NPF) has increased significantly with the strict implementation of anthropogenic SO 2 emission reductions globally. However, even considering the enhancing effect of methylamine (MA), identified as the strongest enhancer in MSA-driven NPF, the MSA-driven nucleation rates have been undervalued from the nucleation mechanism of the present theoretical simulation compared to field observations. So, it is vital to evaluate the participation and enhancement of MSA-MA clusters nucleation by the third atmospheric molecule. Herein, the role of trifluoroacetic acid (TFA), which has strong acidity and hydrogen bonding capabilities and is one of the most abundant atmospheric organic substances, has been investigated in the MSA-MA nucleation at different ambient atmospheres by quantum chemical calculations and atmospheric cluster dynamics code (ACDC) simulations. The results indicated that the enhancement strength R of TFA increased with decreasing temperature, up to 7.28-fold at 218.15 K, and is most remarkable in regions with insufficient MSA and relatively larger amounts of TFA and MA. The present results also revealed that TFA plays different roles under different atmospheric conditions. A "catalyst" role of TFA was found in the formation of MSA-MA-based clusters under relatively low temperatures (such as during winter or the top of troposphere at higher altitudes) and medium concentrations of TFA and MA. Whereas in the vicinity of major sources of TFA and MA emission (with the highest [TFA] and [MA]), TFA acted as a "direct participant" in the formation of nucleus clusters during winter or the top of troposphere (218.15 K). These new insights may be useful in understanding the perspective of the realistic role of TFA in MSA-MA-driven NPF, especially in the intensive human activity and industrial pollution serious of global megacities with winter of dry climate, or western China, Africa and the Arctic remote regions with scant precipitation and the abundant TFA pollutants sources. • TFA can enhance the formation rates of MSA-MA-based clusters at lower T and [MSA] as well as higher [TFA] and [MA]. • TFA can act as both a "catalyst" and a "participator" in the growth of MSA-MA clusters. • TFA is critical for NPF in the region of insufficient MSA and relatively larger amounts of TFA and MA. • This work reveals the realistic role of TFA in MSA-MA-driven NPF, especially in remote regions with scant precipitation. [ABSTRACT FROM AUTHOR]