A comparative study of nucleation parameterizations: 1. Examination and evaluation of the formulations



[1] Large uncertainty exists in the nucleation parameterizations that may be propagated into climate change predictions through affecting aerosol direct and indirect effects. These parameterizations are derived either empirically from laboratory/field measurements or from theoretical models for nucleation rates. A total of 12 nucleation parameterizations (7 binary, 3 ternary, and 2 power laws) that are currently used in three-dimensional air quality models are examined comparatively under a variety of atmospheric conditions from polluted surface to very clean mesosphere environments and evaluated using observations from several laboratory experiments and a field campaign conducted in a sulfate-rich urban environment in the southeastern United States (i.e., Atlanta, Georgia). Significant differences (by up to 18 orders of magnitude) are found among the nucleation rates calculated with different parameterizations under the same meteorological and chemical conditions. All parameterizations give nucleation rates that increase with the number concentrations of sulfuric acid but differ in terms of the magnitude of such increases. Differences exist in their dependencies on temperatures, relative humidity, and the mixing ratios of ammonia in terms of both trends and magnitudes. Among the 12 parameterizations tested, the parameterizations of Kuang et al. (2008), Sihto et al. (2006), and Harrington and Kreidenweis (1998) give the best agreement with the observed nucleation rates in most laboratory studies and in Atlanta during a summer season field campaign and either do not exceed or rarely exceed the upper limits of the nucleation rates (i.e., the dimer formation rate) and new particle formation rates (i.e., the formation rate of particles with 2 nm diameter). They are thus the most plausible nucleation parameterizations for applications in the planetary boundary layer of polluted sulfate-rich urban areas. Limitation with the two power laws are that they were derived empirically based on observations at specific locations under certain atmospheric conditions that may be different from laboratory measurement conditions and those at other locations and that they do not consider RH and T dependence. By contrast, the ternary nucleation parameterization of Napari et al. (2002) should not be used because it grossly overpredicts the observed nucleation rates, often exceeding the upper limit dimer or new particle formation rates, and giving an enhancement factor due to the presence of ammonia and a dependence on relative humidity that are inconsistent with laboratory measurements. The binary nucleation parameterization of Wexler et al. (1994) and Kulmala et al. (1998b) also should not be used because the former gives nucleation rates exceeding the upper limits under most atmospheric conditions and the latter contains technical mistakes in its formula.