A Comparative Study of Homogenous Nucleation Parameterizations for 3-D Atmospheric Models

Nucleation provides a significant source of new particles and affects number and mass concentrations and size distributions of fine particulate matters (PM2.5) that have important chemical, radiative, health and visibility impacts. Large uncertainty exists in the nucleation parameterizations that are derived either empirically from laboratory experiments or the full kinetic models that are based on classical binary and ternary nucleation theories. Use of different nucleation parameterizations in 3-D models may introduce significant uncertainties in model predictions of production rates of new particles and number concentrations of PM2.5.

In this study, seven binary and one ternary nucleation parameterizations are examined under a variety of atmospheric conditions with temperatures of 240-300 K, relative humidities of 5-95%, number concentrations of sulfuric acid of 10E4-10E11 molecules cm-3 and mixing ratios of ammonia of 0.1-100 ppt. Significant differences are found among the binary nucleation rates calculated with different parameterizations (e.g., by 7 orders of magnitude under a temperature of 258 K, a relative humidity of 50%, and an ambient sulfuric acid concentration of 10E9 molecules cm-3) and between the binary and ternary nucleation rates (e.g., by 3-4 orders of magnitude under a temperature of 258 K, a relative humidity of 50%, an ambient sulfuric acid concentration of 10E9 molecules cm-3, and an ambient ammonia concentration of 10 ppt). These parameterizations will be further evaluated in a 3-D air quality model using available measurements to assess the appropriateness of these parameterizations in reproducing number concentrations and size distributions of PM2.5, the associated uncertainties and implications.