Abstract
Abstract. Secondary particles formed via new particle formation (NPF) dominate cloud condensation nuclei (CCN) abundance in most parts of the troposphere and are important for aerosol indirect radiative forcing (IRF). Laboratory measurements have shown that certain organic compounds can significantly enhance the binary nucleation of sulfuric acid and H2O. According to our recent study comparing particle size distributions measured in nine forest areas in North America with those predicted by a global size-resolved aerosol model, current H2SO4–organics nucleation parameterizations appear to significantly overpredict NPF and particle number concentrations in summer. The lack of temperature dependence in the current H2SO4–organics nucleation parameterization has been suggested to be a possible reason for the observed overprediction. In this work, H2SO4–organics clustering thermodynamics from quantum chemical studies has been employed to develop a scheme to incorporate temperature dependence into H2SO4–organics nucleation parameterization. We show that temperature has a strong impact on H2SO4–organics nucleation rates and may reduce the nucleation rate by ∼ 1 order of magnitude per 10 K of temperature increase. The particle number concentrations in summer over North America based on the revised scheme is a factor of more than 2 lower, which is in much better agreement with the observations. With the temperature-dependent H2SO4–organics nucleation parameterization, the summer CCN concentrations in the lower troposphere in the Northern Hemisphere are about 10–30 % lower compared to the temperature-independent parameterization. This study highlights the importance of the temperature effect and its impacts on NPF in the global modeling of aerosol number abundance.
Highlights
Atmospheric particles, by acting as cloud condensation nuclei (CCN), modify cloud properties and precipitation, indirectly affecting the hydrological cycle and the climate
Secondary particles formed via nucleation dominate particle number concentrations in many parts of the troposphere (Spracklen et al, 2008; Pierce and Adams, 2009; Yu and Luo, 2009), and global simulations indicate that nucleation schemes and parameterizations have a strong effect on the aerosol indirect radiative forcing (IRF) estimations (Wang and Penner, 2009; Kazil et al, 2010; Yu et al, 2012)
It is important to understand the mechanisms of new particle formation (NPF) and the key parameters controlling the contribution of NPF to CCN formation under a wide range of varying atmospheric conditions and to validate their representation in regional and global climate models
Summary
Atmospheric particles, by acting as cloud condensation nuclei (CCN), modify cloud properties and precipitation, indirectly affecting the hydrological cycle and the climate. Secondary particles formed via nucleation dominate particle number concentrations in many parts of the troposphere (Spracklen et al, 2008; Pierce and Adams, 2009; Yu and Luo, 2009), and global simulations indicate that nucleation schemes and parameterizations have a strong effect on the aerosol IRF estimations (Wang and Penner, 2009; Kazil et al, 2010; Yu et al, 2012). A number of laboratory chamber studies indicate that certain organic species can significantly enhance NPF (e.g., Zhang et al, 2004; Riccobono et al, 2014).
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