Investigation of ship-plume chemistry using a newly-developed photochemical/dynamic ship-plume model

Abstract

A photochemical/dynamic ship-plume model, which can consider the ship-plume dynamics and ship-plume chemistry, simultaneously, was developed to gain a better understanding of atmospheric impact of ship emissions. The model performance was then evaluated by a compari-son with the observation data measured on a NOAA WP-3D flight during the Intercontinental Transport and Chem-ical Transformation 2002 (ITCT 2K2) airborne field cam-paign. The simulation conditions and parameters, such as meteorological conditions, emission rates, and background gas and particulate species concentrations, were obtained di-rectly and/or inferred indirectly from the ITCT 2K2 observa-tion data. The model-predicted concentrations showed good agreement with the observed concentrations of five ambi-ent species (NOx, NOy, ozone, HNO3, and H2SO4) at the eight plume transects by the WP-3D flight with strong cor-relations around the 1:1 line (0.64< R <0.85). In addition, a set of tests were carried out to approximate the magnitude of the reaction probability of HNO3 onto sea-salt particles in the model-observation comparison framework. These re-sults suggest tht the reaction probability of HNO3 onto sea-salt particles may be in the order of 0.05-0.1. The equiv-alent NOx lifetime throughout the "entire plume" was also estimated from photochemical/dynamic ship-plume model-ing. The NOx lifetimes estimated throughout the entire ship plume ranged from 2.64 h to 3.76 h under stable to neutral stability conditions. The short NOx lifetime over the en-tire ship plume clearly shows that the ship-plume chemistry shortens the NOx lifetime considerably. Therefore, the ship-plume chemistry model should be used to model the changes in ship-plume chemical compositions and better evaluate the atmospheric impact of ocean-going ship emissions.