Evaluation of nucleation algorithms and their impacts on simulated aerosol number and size distributions and cloud properties

Atmospheric aerosols affect regional/global air quality and meteorology as well as long-term climate through climate-chemistry-aerosol-cloud-radiation interactions. The impacts of aerosol feedbacks, from direct effects on radiation to indirect effects by acting as cloud condensation nuclei and modifying cloud properties, strongly depend on the number and mass concentrations as well as size distribution of aerosols. The formation of new particles, widely observed at various locations and conditions, is one of the most important processes affecting aerosol number concentrations and size distributions. A number of theories and empirical methods have been proposed to simulate new particle formation, each with its own merits and limitations. Furthermore, large uncertainties exist in the simulated formation rates of new particles.

In this study, several homogeneous nucleation parameterizations (e.g., binary, ternary, and empirical power-law), and one ion-mediated nucleation parameterization, will be evaluated in the AERO5 aerosol module in the U.S. Environmental Protection Agency (EPA) Model-3 Community Multiscale Air Quality (CMAQ) modeling system. Simulations with these nucleation parameterizations will be conducted for August 2002 over a domain in the southeastern U.S. at a 4-km horizontal resolution. The results will be evaluated against field measurement data from the 2002 Aerosol Nucleation and Real Time Characterization Experiment (ANARChE) in Atlanta, Georgia, as well as additional observations over rural/remote/coastal/marine areas from literatures. Plausible parameterizations identified from regional simulations will be incorporated into the Global-through-Urban Weather Research and Forecasting model with Chemistry (GU-WRF/Chem) to further evaluate their performance on a global scale using published observations under representative atmospheric conditions. The impacts of different nucleation algorithms on simulated aerosol number concentrations, aerosol size distribution, and cloud properties will be examined.