The Impact of Shipping on Urban Air Pollution in Auckland and Tauranga, New Zealand

Abstract

Transport sources have been identified as significant contributors to urban air pollution within cities, with a surplus of literature addressing the influence of motor vehicles. In contrast, there is a dearth of literature regarding the impact of shipping vessel emissions on local scale air quality. As a result the interaction between the complex vessel characteristics and meteorological processes is poorly understood. Statistical analysis has been undertaken on pollutant monitoring records with co – located wind speed, wind direction, temperature and humidity data for 2011 and 2012, from three monitoring sites near the Ports of Auckland and two near the Port of Tauranga. The fixed site monitoring records were used to investigate the influence of meteorology on pollutant dispersion. This was carried out graphically, through the use polar plots and statistically through the use of time series analysis and Kruskal – Wallis analysis of variance. Comparison to vessel berth records was carried out in order to examine how observed sulphur dioxide (SO2) varies between the number of vessels berthed and the type of vessel in port. Increasing SO2 concentrations in response to increasing wind speed were found at all Auckland sites with vessel emissions being the dominant source. In Tauranga, SO2 concentrations were shown to both increase and decrease with increasing wind speed, however local industrial and traffic sources dominated emissions. Variation in pollutant concentration with distance was found to likely be a result of dominant meteorology and surrounding topography, and not only distance from the vessel source at each site. Mid – morning and midday peaks were observed in SO2 concentrations at Auckland sites, coinciding with periods of an unstable atmosphere, therefore likely due to peak ferry departures and arrivals during these periods. At Totara, SO2 emissions from vessels were observed during day time hours, however as at Ballance, local traffic and industrial sources dominated at night time hours. Though increasing emissions associated with increasing vessel numbers are seen at one site in Auckland, variation in emissions between the sites were likely to be a result of proximity of monitors to particular vessel berths and the dominant wind speed and direction during these periods. Increased SO2 attributed to the presence of passenger vessels was only observed at one Auckland site. Similarly to vessel number, variation in emissions by vessel type were likely a result of individual vessel characteristics within vessel types and the location of berths in relation to monitoring sites.