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No. 316: Survey of air pollution from cruise ships in Copenhagen and Aarhus

Jensen, S.S., Winther, M., Løfstrøm, P., Frohn, L.M. 2019. Kortlægning af luftforurening fra krydstogtskibe. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 78 s. - Videnskabelig rapport nr. 316. http://dce2.au.dk/pub/SR316.pdf

Summary

Aim and background

The purpose of this report is to assess the number of cruise ships and their emissions in Copenhagen Port and Port of Aarhus, and how this affects air quality. Air quality calculations are carried out in the nearby urban areas in Copenhagen and Aarhus and on a more detailed scale in the vicinity of the quays.

The study

By way of introduction, a statistical overview of cruise ships in Danish ports in 2017 was established based on information from Statistics Denmark.

The administrations of Copenhagen Port and Port of Aarhus have provided detailed statistics on cruise ships calling into port in 2017, berthing slots and quay location. The location of the quays have been digitized based on maps provided by the ports.

By internet lookups (marinetraffic.com, cruiseline’s homepage, ship yards etc.) using the ship’s name or IMO code (International Maritime Organization), it is possible to determine a number of parameters for the ship such as construction year, engine type, total installed engine power, scrubber installation, etc. These data makes it possible to determine the fuel consumption and emission factors for the precise calculation of the emissions. Similarly, a number of physical parameters has been determined such as height of ship above the water line, chimney height above the water line, volume flow and exhaust gas temperature based on previous studies (Olesen & Berkowicz, 2005).

Air quality calculations have been carried out with the OML-model for 2017 based on the emission inventory and the physical parameters. In addition to emissions, meteorological data and background concentrations are also included in the OML-calculations. Firstly, air quality calculations are performed for a larger grid for each city on a spatial resolution of 200 m x 200 m in order to assess how cruise ships affect air quality in the urban area around the ports. Secondly, air quality calculations are carried out on a smaller grid with a finer spatial resolution to assess the air quality in the vicinity of the quays. The spatial resolution is 100 m x 100 m for Copenhagen Port and 50 m x 50 m for Port of Aarhus. Calculations are carried out for the annual mean of NO2 (nitrogen dioxide) and of PM2.5 (mass of particles less than 2.5 micrometers), as well as for the 19th highest hourly value of NO2 to represent peak values. Limit values exist for all these indicators. The geographic variation in concentrations is shown with isocurves on aerial photos. An isocurve is a line with the same concentration level.

A meteorological year with more frequent easterly wind was identified to assess the impact to air quality. More frequent wind directions from East will transport air pollution from the cruise ships towards the urban areas in both Copenhagen and Aarhus due to their location. The selected meteorological year is 2002.

The concentration contribution of the cruise ships has moreover been calculated at different heights for the small grids in the ports to assess the exposure of high-rise buildings. Calculations have been performed for 25 m, 50 m and 70 m.

Main conclusions

Calls into Danish ports

The statistical analysis of berthing of cruise ships showed that the vast majority of all calls to Danish ports takes place in Copenhagen Port with a share of 70% in 2017. The second largest is Port of Aarhus with 8% and then Port of Rønne with 6%, while the rest is among other ports. The Statistical analysis was based on Statistics Denmark. Separate information was obtained from the administration of Port of Aalborg. The comparison between Port of Aalborg and Port of Aarhus showed that Port of Aalborg actually had 6% more calls than the Port of Aarhus. The overall berthing time in Port of Aalborg was 19% lower, and fuel consumption and NOx emissions are nearly 60% lower and 65% lower for PM2.5 emissions, and the cruise ships are also smaller on average.

Emissions from cruise ships

Total emission from cruise ships in Copenhagen Port in 2017 was 284.5 tons of NOx and 10.0 tons of PM2.5. By way of comparison, the total emission from all emission sources within the large calculation grid in Copenhagen was 1,669 tons of NOx and 175 tons of PM2.5. Wood stoves etc. (SNAP2) emitted 23 tons of NOx and 40 tons of PM2.5, while road transportation (SNAP7) contributed with 878 tons of NOx and 52 tons of PM2.5. Hence, the emissions of the cruise ships constitute approx. 17% of NOx emissions and 6% of PM2.5 emission. In relation to road transport, the cruise ships contribute approx. 32% of NOx emissions and 19% of PM2.5 emissions.

In Port of Aarhus, the total emission of cruise ships in 2017 was 26.2 tons of NOx and 1.3 tons of PM2.5. The total emission from all emission sources within the large calculation grid in Aarhus was 812 tons of NOx and 100 tons of PM2.5. Wood stoves etc. (SNAP2) emitted 23 tons of NOx and 45 tons of PM2.5, while road transport (SNAP7) contributed with 385 tons of NOx and 23 tons of PM2.5. The emissions of the cruise ships constitute approx. 3% of total NOx emissions and 1% of total PM2.5 emissions. Hence, the emissions of the cruise ships constitute approx. 7% of NOx emissions and 6% of PM2.5 emissions in relation to road transport.

A comparison of the emissions from an average cruise ship with the emissions from an average passenger car in city traffic shows, that emissions from a cruise ship is equivalent to emissions from about 3,500 cars for NOx and around 5,000 cars for PM2,5 exhaust calculated per time unit (g/s).

Exceedances of limit value at heights of 25 m to 70 m

In order to assess the impact to air quality of other heights than ground level of 1.5 m, calculations were performed for heights of 25 m, 50 m and 70 m. For example, the buildings at Langeliniekajen in Copenhagen Port are approx. 25 m of height, and there are other buildings in the port, which are significantly taller. In addition, there are plans to continue expansion of housing in the port. 

The concentration contribution of the cruise ships to air pollution increases generally with height. This is expected, since the exhaust from cruise ships occurs at a relatively high elevation, and concentrations will be higher at similar heights than at the surface. The plume from the chimney will be more diluted when it reaches the surface whereas at elevated heights it will be less diluted.

In Copenhagen Port, the maximum contribution to the annual mean concentration of NO2 is approx. 9 µg/m3 at 50 m and 70 m in 2017, which is significant compared to the background level of 16 µg/m3, but still significantly below the limit at 40 µg/m3.

The limit value was not exceeded for calculations of the 19th highest hourly value for NO2 at ground level. However, the limit value is reached at a height of 25 m and significantly exceeded at heights of 50 m and 70 m. The maximum values exceed the limit value of 200 µg/m3 several times. Hence, the cruise ships contribute significantly to exceedances of the limit value of the 19th highest hourly value for NO2 in Copenhagen Port.

The concentration contribution of the cruise ships to the annual mean concentration of PM2.5 also generally increases with height. The maximum contribution is 2.3 µg/m3 in the height of 50 m in 2017 in Copenhagen Port, which is significant in relation to a background level of 10 µg/m3, but far below the limit value of 25 µg/m3.

The same pattern is also seen for the Port of Aarhus. The limit value for the 19th highest hourly value for NO2 is also substantially exceeded in heights of 25 m, 50 m and 70 m. 

Air pollution from cruise ships in the Copenhagen Port and Port of Aarhus is therefore concentrated to the vicinity of the quays for cruise ships, and the limit value for the 19th highest hourly value of NO2 was significantly exceeded in the examined heights of 25 m, 50 m and 70 m.

Impact of cruise ships on air quality at the surface (1.5 m height)

Cruise ship emissions affect annual mean concentrations of NO2 and PM2.5 at the surface (1.5 m height) insignificantly in the adjacent urban areas in Copenhagen and Aarhus in 2017.

However, the vicinity of the quays is influenced by the emission of the cruise ships. In Copenhagen Port the maximum contribution from cruise ships to the annual mean concentration of NO2 is 1 µg/m3 in 2017 which occurs at the Northwest corner of Refshaleøen. For comparison, the background level is 16 µg/m3 at the urban background station of the H.C. Ørsted Institute, and the limit value is 40 µg/m3.

The highest contribution to the annual mean concentration of PM2.5 is 0.08 µg/m3, and occurs East of Langeliniekajen and Oceankajen. The concentration contribution from cruise ships is very small compared to the background level of PM2.5 at the urban background station of the H.C. Ørsted Institute, which is 10 µg/m3 for 2017. The limit value is 25 µg/m3.

Cruise ship emissions affect to some extent the peak values of concentrations, where the indicator 19th highest hourly value of NO2 is used. The highest peak value contribution is 7µg/m3 that occur within about 500 meters of the quays in Copenhagen Port. The 19th highest hourly value of NO2 is under the limit value of 200 µg/m3.

Calculated levels at the surface (1.5 m height) are well below the limit values for annual mean concentrations and peak values, and contributions from the cruise ships are very modest.

The same pattern is seen for Port of Aarhus, however, with lower contributions from the cruise ships.

Meteorological year with frequent eastern wind directions

The analysis of the meteorological year of 2002 with much more frequent eastern wind directions showed that the distribution of air pollution from cruise ships is affected and different from 2017. As expected, the highest concentration contribution of the cruise ships lies more to the West of the quays than in 2017. The contributions are still very small at ground level (1.5 m).