Gaseous Methylamines over the Yangtze River Delta in China: Contributions from Different Source Types and Comparisons of WRF-Chem Simulations with Observations

Amines have received increasing attentions in recent years because of their potential role in new particle formation in atmosphere and particulate chemistry. High concentrations of amines are expected to be limited to the vicinity of source regions due to their short lifetime, highlighting the necessity to have a better understanding of contributions of emissions from different source types. Here, the concentrations and spatial distributions of gaseous methylamines over Yangtze River Delta, one of highly polluted regions in China, have been investigated using WRF-Chem with multiple nested domains. In contrast to previous modeling studies (very limited) assuming a fixed ratio (FR) of amines to total ammonia emission, we derive source-dependent ratios (SDR) that distinguish C1-amine (CH₃NH₂), C2-amines (C₂H₇N), C3-amines (C₃H₉N) emissions from six different source types (chemical facility, industry, agriculture, residential, traffic, and ship). The amines-to-ammonia mass emission ratios for chemical facility, industry, agriculture, residential, traffic, and ship sources are, respectively, 0.004, 0.004, 0.001, 0.0025, 0.001, and 0.001for C1-amine, 0.007, 0.007, 0.0015, 0.01, 0.01, and 0.01for C2-amines, and 0.0009, 0.0009, 0.0003, 0.0008, and 0.001, and 0.001 for C3-amines. The simulated concentrations of C1-, C2-, and C3-amines, based on both fixed and source-dependent ratios, have been compared with field measurements obtained at a suburban site in Nanjing and at an urban site in Shanghai, China. The simulated amines concentrations based on SDR are generally in much better agreement with measurements. C1-, C2-, and C3-amines concentrations in the surface layer are in the range of 2-20 pptv, 5-40 pptv, and 0.5-3 pptv, and high concentrations of these amines are limited to the boundary layer. The implications of high concentrations of amines in the region will be discussed.