Abstract
Abstract. Understanding new particle formation and growth is important because of the strong impact of these processes on climate and air quality. Measurements to elucidate the main new particle formation mechanisms are essential; however, these mechanisms have to be implemented in models to estimate their impact on the regional and global scale. Parameterizations are computationally cheap ways of implementing nucleation schemes in models, but they have their limitations, as they do not necessarily include all relevant parameters. Process models using sophisticated nucleation schemes can be useful for the generation of look-up tables in large-scale models or for the analysis of individual new particle formation events. In addition, some other important properties can be derived from a process model that implicitly calculates the evolution of the full aerosol size distribution, e.g., the particle growth rates. Within this study, a model (SANTIAGO – Sulfuric acid Ammonia NucleaTIon And GrOwth model) is constructed that simulates new particle formation starting from the monomer of sulfuric acid up to a particle size of several hundred nanometers. The smallest sulfuric acid clusters containing one to four acid molecules and a varying amount of base (ammonia) are allowed to evaporate in the model, whereas growth beyond the pentamer (five sulfuric acid molecules) is assumed to be entirely collision-controlled. The main goal of the present study is to derive appropriate thermodynamic data needed to calculate the cluster evaporation rates as a function of temperature. These data are derived numerically from CLOUD (Cosmics Leaving OUtdoor Droplets) chamber new particle formation rates for neutral sulfuric acid–water–ammonia nucleation at temperatures between 208 and 292 K. The numeric methods include an optimization scheme to derive the best estimates for the thermodynamic data (dH and dS) and a Monte Carlo method to derive their probability density functions. The derived data are compared to literature values. Using different data sets for dH and dS in SANTIAGO detailed comparison between model results and measured CLOUD new particle formation rates is discussed.
Highlights
The formation of new aerosol particles from the gas phase is the most important source of cloud condensation nuclei (CCN) in the free and upper troposphere (Dunne et al, 2016; Gordon et al, 2017)
Binary new particle formation (NPF) from sulfuric acid and water is thought to be an important mechanism at cold conditions that can be enhanced by ions (Lee et al, 2003; Kirkby et al, 2011; Duplissy et al, 2016)
The importance of ammonia in terms of NPF is highlighted by recent modeling studies, where a large fraction of CCN originates from ternary H2SO4-H2O-NH3 nucleation (Dunne et al, 2016; Gordon et al, 2017)
Summary
The formation of new aerosol particles from the gas phase (nucleation) is the most important source of cloud condensation nuclei (CCN) in the free and upper troposphere (Dunne et al, 2016; Gordon et al, 2017). Binary new particle formation (NPF) from sulfuric acid and water is thought to be an important mechanism at cold conditions that can be enhanced by ions (Lee et al, 2003; Kirkby et al, 2011; Duplissy et al, 2016). The ternary system involving ammonia besides sulfuric acid and water can yield significantly enhanced NPF rates (Ball et al, 1999; Benson et al, 2009; Glasoe et al, 2015; Kirkby et al, 2011; Kürten et al, 2016). The detection of ammonia above several parts per trillion by volume in the upper troposphere by recent satellite measurements supports these findings (Höpfner et al, 2016). An aircraft campaign up to ∼ 5 km altitude measured elevated NH3
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