Abstract
Abstract. A high resolution chemical transport model of the marine boundary layer is designed in order to investigate the detailed chemical evolution of a ship plume in a tropical location. To estimate systematic errors due to finite model resolution, otherwise identical simulations are run at a range of model resolutions. Notably, to obtain comparable plumes in the different simulations, it is found necessary to use an advection scheme consistent with the Large Eddy Model representation of sub-grid winds for those simulations with degraded resolution. Our simulations show that OH concentration, NOx lifetime and ozone production efficiency of the model change by 8%, 32% and 31% respectively between the highest (200 m×200 m×40 m) and lowest resolution (9600 m×9600 m×1920 m) simulations. Interpolating to the resolution of a typical global composition transport model (CTM, 5°×5°), suggests that a CTM overestimates OH, NOx lifetime and ozone production efficiency by approximately 15%, 55% and 59% respectively. For the first time, by explicitly degrading the model spatial resolution we show that there is a significant reduction in model skill in accurately simulating the aforementioned quantities due to the coarse resolution of these CTMs and the non-linear nature of atmospheric chemistry. These results are significant for the assessment and forecasting of the climate impact of ship NOx and indicate that for realistic representation of ship plume emissions in CTMs, some suitable parametrisation is necessary at current global model resolutions.
Highlights
Oxides of nitrogen (NOx) play a central role in determining the composition of the atmosphere
A range of identical simulations are run in which we vary the spatial resolution to investigate the effect of resolution on the OH concentration, lifetime of NOx and ozone production efficiency (OPE)
We find that the impacts of the ship NO emissions on the marine boundary layer (MBL) chemistry are highly dependent on the model resolution
Summary
Oxides of nitrogen (NOx) play a central role in determining the composition of the atmosphere. Song et al (2003) examined the evolution of a plume mixing with the ambient air at different latitudes and under day vs night conditions and diagnosed differences in NOx lifetime values up to a factor of 10 between the background and the plume air It is well-established that, due to the nonlinearity of Ox-HOx-NOx chemistry, artificially rapid mixing in instantaneous dilution scenarios can lead to systematic changes in net radical concentrations, and to errors in the tendencies of many radiatively active gases including ozone (Chatfield and Delaney, 1990; Liang and Jacobson, 2000). Ship emissions in global 3-D CTMs are parameterized, if they are included, and typically cause models to significantly overestimate NOx and O3 in the MBL (Kasibhatla et al, 2000; Davis et al, 2001; Endresen et al, 2003) This overestimate is usually partially attributed to the combination of coarse spatial resolution and the non-linear nature of the Ox-HOx-NOx chemistry (Song et al, 2003).
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