Estimating the Lower Limit of the Impact of Amines on Nucleation in the Earth's Atmosphere

Amines, organic derivatives of NH3, are important common trace atmospheric species that can enhance new particle formation in the Earth's atmosphere under favorable conditions. While methylamine (MA), dimethylamine (DMA) and trimethylamine (TMA) all efficiently enhance binary nucleation, MA may represent the lower limit of the enhancing effect of amines on atmospheric nucleation. In the present paper, we report new thermochemical data concerning MA-enhanced nucleation, which were obtained using the DFT PW91PW91/6-311++G (3df, 3pd) method, and investigate the enhancement in production of stable pre-nucleation clusters due to the MA. We found that the MA ternary nucleation begins to dominate over ternary nucleation of sulfuric acid, water and ammonia at [MA]/[NH3] > similar to 10(-3). This means that under real atmospheric conditions ([MA] similar to 1 ppt, [NH3] similar to 1 ppb) the lower limit of the enhancement due to methylamines is either close to or higher than the typical effect of NH3. A very strong impact of the MA is observed at low RH; however it decreases quickly as the RH grows. Low RH and low ambient temperatures were found to be particularly favorable for the enhancement in production of stable sulfuric acid-water clusters due to the MA.