10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Important Role of Ammonia in New Particle Formation in the Earth’s Atmosphere
FANGQUN YU, Alexey Nadykto, Gan Luo, Jason Herb, James Schwab, Joseph P. Marto, Junying Sun, Xiaojing Shen, Kirill Nazarenko, Lyudmila Uvarova, University at Albany
Abstract Number: 1632 Working Group: Aerosol Modeling
Abstract New particle formation (NPF, or nucleation) is an important source of atmospheric particles and cloud condensation nuclei (CCN), impacting air quality, hydrological cycle, and climate. Ammonia is the most abundant base molecule in the atmosphere, and has been observed to enhance nucleation in a number of laboratory studies. Despite intensive research over the past two decades, questions remain about the role of ammonia in NPF, including the detailed nature of the physico-chemical processes underlying the observed impacts of NH3 on aerosol nucleation rates and properties. Here we employ the thermodynamic data derived from both quantum calculations and experimental measurements to quantify the physio-chemical processes of NH3 nucleation enhancement, and present a comprehensive kinetically-based H2SO4-H2O-NH3 ternary ion-mediated nucleation (TIMN) that explicitly resolves the dependence of nucleation rates on all major controlling parameters. We show that the presence of NH3 lowers the nucleation barriers for neutral, positively charged, and negatively charged clusters differently, as a result of large difference in the binding strength of NH3, H2O, and H2SO4 to small clusters of different charge states. The model reveals the general preference of nucleation on negative ions, the necessity of relatively high [NH3] to initiate nucleation on positive ions, and even higher [NH3] required to achieve neutral nucleation. The predicted dependence of TIMN rates on [NH3], [H2SO4], ionization rates, temperature, and relative humidity agrees well with laboratory measurements. The newly developed TIMN scheme has been implemented into regional and global models (WRF-Chem, GEOS-Chem, and CESM-CAM5), and evaluated against NPF measurements taken at a site in the heavily polluted area around Beijing, China, and another site in the relatively less polluted northeastern region of the US. We show that TIMN schemes reproduce well the observed NPF events and non-events, and ammonia plays an important role in promoting NPF in the lower troposphere. The implications of the results will be discussed.