Abstract
Abstract. This study investigates the evolution of ship-emitted aerosol particles using the stochastic particle-resolved model PartMC-MOSAIC (Particle Monte Carlo model-Model for Simulating Aerosol Interactions and Chemistry). Comparisons of our results with observations from the QUANTIFY (Quantifying the Climate Impact of Global and European Transport Systems) study in 2007 in the English Channel and the Gulf of Biscay showed that the model was able to reproduce the observed evolution of total number concentration and the vanishing of the nucleation mode consisting of sulfate particles. Further process analysis revealed that during the first hour after emission, dilution reduced the total number concentration by four orders of magnitude, while coagulation reduced it by an additional order of magnitude. Neglecting coagulation resulted in an overprediction of more than one order of magnitude in the number concentration of particles smaller than 40 nm at a plume age of 100 s. Coagulation also significantly altered the mixing state of the particles, leading to a continuum of internal mixtures of sulfate and black carbon. The impact on cloud condensation nuclei (CCN) concentrations depended on the supersaturation threshold S at which CCN activity was evaluated. For the base case conditions, characterized by a low formation rate of secondary aerosol species, neglecting coagulation, but simulating condensation, led to an underestimation of CCN concentrations of about 37% for S = 0.3% at the end of the 14-h simulation. In contrast, for supersaturations higher than 0.7%, neglecting coagulation resulted in an overestimation of CCN concentration, about 75% for S = 1%. For S lower than 0.2% the differences between simulations including coagulation and neglecting coagulation were negligible. Neglecting condensation, but simulating coagulation did not impact the CCN concentrations below 0.2% and resulted in an underestimation of CCN concentrations for larger supersaturations, e.g., 18% for S = 0.6%. We also explored the role of nucleation for the CCN concentrations in the ship plume. For the base case the impact of nucleation on CCN concentrations was limited, but for a sensitivity case with higher formation rates of secondary aerosol over several hours, the CCN concentrations increased by an order of magnitude for supersaturation thresholds above 0.3%.
Highlights
Ship-emitted particulates are a mix of different particle types. These include combustion particles consisting mainly of black carbon (BC), primary organic carbon (POC), sulfate and ash, and volatile particles forming from nucleation of sulfuric acid during plume expansion (Song et al, 2003; Cooper, 2003; Petzold et al, 2008)
We show the comparison of measured and modeled total number concentrations from a single plume event, as well as the comparison of measured and modeled size distributions from the shipping corridor
We quantify the role of coagulation and condensation for the evolution of aerosol mixing state and their impacts on cloud condensation nuclei (CCN) properties
Summary
Emissions from ocean-going ships have been receiving increased attention in recent years due to their adverse effects on coastal and global air quality (Ault et al, 2009; Endresen et al, 2003; González et al, 2011; Moldanová et al, 2009; Eyring et al, 2007), human health (Corbett et al, 2007; Winebrake et al, 2009) and the climate system (Capaldo et al, 1999; Eyring et al, 2010; Lawrence and Crutzen, 1999). For this study we represented the evolving particle distribution of ship-emitted aerosols with a new modeling approach, the stochastic particle-resolved aerosol model PartMC-MOSAIC (Particle Monte Carlo model-Model for Simulating Aerosol Interactions and Chemistry) (Riemer et al, 2009) This model explicitly resolves the composition of individual particles in a given aerosol population and is uniquely suited to investigate the evolution of particle mixing states and the associated particle properties. PartMC-MOSAIC has been used for detailed studies on the particle level, for example to derive aging time-scales of black carbon aerosol (Riemer et al, 2010), to investigate the heterogeneous oxidation of soot surfaces (Kaiser et al, 2011), to quantify the impacts of black carbon mixing state on black carbon nucleation scavenging (Ching et al, 2012), and to explore the sensitivity of cloud condensation nuclei activity to particle characteristics at emission (Fierce et al, 2013).
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