Propionamide participating in H₂SO₄-based new particle formation: a theory study

Propionamide (PA), an important pollutant emitted into the atmosphere from a variety of sources, is abundant in many areas worldwide, and could be involved in new particle formation (NPF). In this study, the enhancement of the H₂SO₄ (SA)-based NPF by PA was evaluated through investigating the formation mechanism of (PA) (SA) (m = 0-3 and n = 0-3) clusters using computational chemistry and kinetics modeling. Our study proved that the formation of all the PA-containing clusters is thermodynamically favorable. Furthermore, the [double bond, length as m-dash]O group in PA plays an important role in the clusters with more PA than SA, and the basicity of bases exerts a greater influence with an increasing amount of SA. We demonstrate that although the enhancing potential of PA is lower than that of the strongest enhancers of SA-based NPF such as methylamine (MA) and dimethylamine (DMA), PA can enhance the SA-based NPF at the parts per billion (ppb) level, which is typical for concentrations of C₃-amides in, for example, urban Shanghai (China). The monomer evaporation is the dominant degradation pathway for the (PA) (SA) clusters, which differs from that of the SA-DMA system. The formation rate of PA-containing clusters is comparable to the rate coefficients for PA oxidation by hydroxyl (OH) radicals, indicating that participating in the SA-based NPF is a crucial sink for PA.