Comparison of large-scale ship exhaust emissions across multiple resolutions: From annual to hourly data

Ship exhaust emissions need to be calculated at fine spatial and temporal resolutions because chemical transport processes depend on meteorological conditions that have a high degree of spatial and temporal variability. These emissions can also occur in environments that are affected by spatially and temporally varying emissions from other sources. Ship exhaust emissions are calculated using activity data from the Automatic Identification System. The activity data are combined with ship specific technical data. Hourly emissions are obtained for 2014 over the region within 300 km of Sydney at approximately 1 km resolution. These data are aggregated regionally and by vessel type to examine variability at different temporal resolutions. Cruise ship emissions vary both seasonally and diurnally, with low activity in winter and high activity in spring and summer. Diurnal variability is associated with a preference for hoteling at berth during the day and cruising at sea overnight. Emissions from the Sydney Harbour ferries have a strong but more complex diurnal variation that is affected by work related commuting. Monthly variability is also described for other ship types that visited the four major ports in the region. Spatial cell activity hours are analysed to explain large differences in the average spatial extent of the emissions at different temporal resolutions, the accuracy with which the hourly emission rates are estimated using longer term emissions, and the suitability of generalised temporal profiles to describe the emissions data. Regression analysis is used to model the spatial extent of the hourly and daily emissions.