Evaluating the contribution of ship exhaust gas emissions to air pollution and the urban carbon footprint: a case study of Durban Port.

Abstract

The Durban Port in South Africa is the busiest port in Africa and has the second largest container terminal in the southern hemisphere. Approximately 60% of the country’s exports and imports pass through this port. It is one of the few ports in the world that is in close proximity to the central business district (CBD). This proximity has a positive spin-off in terms of tourism, recreation and accessibility to transport and other business activities. However, it also has a negative impact to the city’s population due to air pollution resulting from the port activities, particularly from the marine mobile sources. Like many other ports globally, Durban Port suffers from the lack of proper quantification of emissions resulting from ships in the port. The aim of this study was therefore to calculate the pollution from ships in Durban Port between the 1st of April 2012 and the 31st of March 2013 (one year). The activity-based method was utilized to estimate ships emissions of sulphur dioxide (SO2), oxides of nitrogen (NOX), particulate matter (PM10), hydrocarbons (HC) and carbon dioxide (CO2). This method uses emission factors for specific engines, the types of activities (also known as modes of operation) in the port, the time spent on each activity and the load factors per activity. The types of activities considered were manoeuvring, hoteling and loading/unloading. The types of vessels studied were ocean going vessels (OGVs) and harbour crafts. The results indicate that OGVs (particularly container ships) emit higher levels of pollutants than the harbour crafts in Durban Port. This is explained by the higher number of OGVs relative to harbour crafts, and the higher emissions per OGV per operational hour relative to those of harbour crafts. Auxiliary engines accounted for a higher proportion of emissions of NOX and HC when compared to propulsion engines and boilers, while the boilers emitted higher levels of SOX, PM10 and CO2. This is because both the auxiliary engines and the boilers remain operational in all three activities studied. The emissions inventory for Durban Port was compared with other ports globally including JN Port in India, the Port of Los Angeles in the United States and the Port of Copenhagen in Denmark. Cambridge Environmental Research Consultants’ (CERC) Atmospheric Dispersion Modelling System (ADMS) was used to model ambient concentrations of NOX, SO2, and PM10 from ships in port. The results were compared with and found to be below the South African National Ambient Air Quality Standards (NAAQS) published in line with Section 9 of the National Environmental Management: Air Quality Act 39 of 2004. However, the results indicate that emissions from ships are significant and should not be ignored in cumulative air quality assessments and the calculation of the urban carbon footprint.