Miljøprojekt, 978 – Vurdering af krydstogtskibes bidrag til luftforurening

Vurdering af krydstogtskibes bidrag til luftforurening

Summary and conclusions

The present study concerns the contribution to air pollution caused by cruise ships calling at the Port of Copenhagen. The Danish EPA has commissioned the study to be conducted by NERI (NERI is the National Environmental Research Institute, in Danish called DMU). The study can be regarded as a follow-up to a previous, but less detailed study undertaken by the Danish Environmental Assessment Institute (IMV) in 2003, which rose concern that emission of NO_X from cruise ships could cause severe air pollution problems in certain parts of Copenhagen.

The present study is limited to emissions with possible health effects, i.e. NO₂, SO₂ and PM₁₀. It is considerably more detailed than the one mentioned above. The main differences are that the present study takes into account the fact that emission from the cruise ships is distributed among several quays, that the emission takes place only during certain periods of the year, and – very importantly – that background concentrations and atmospheric chemistry have a substantial smoothing effect, when "translating" NO_X emissions to NO₂ concentrations.

A further difference is that the present study concerns only cruise ships, not all ships in the Port of Copenhagen.

The current study is based on information on those cruise ships that actually called at the port of Copenhagen in 2004. A detailed emission inventory has made it possible to avoid several simplifying assumptions of the previous study.

Data for emissions from the cruise ships have been compiled by FORCE Technology. An annex to the present report provides further specifications on the methodology and results of the emission inventory.

When compiling the emission inventory, a principal source of information was a questionnaire sent to the ship agents. It has come as a surprise that it was not reported for any ship that an exhaust cleaning system was in use, even though cleaning systems are known to be installed on at least one ship.

This question has not been pursued further in the context of the present study; the entire set of calculations has been based on the assumption that exhaust-cleaning systems have not been used.

According to the data from 2004, a maximum of 6 cruise ships were present in the harbour at the same time. The total yearly emission of NO_X from cruise ships in the Port of Copenhagen was 145 ton, while the total emission from all ships in the harbour was 600 ton/year.

Atmospheric dispersion calculations have been conducted based on data on emission, physical characteristics of the cruise ships, meteorology and background concentrations. The Danish OML model (OML-Multi 5.03) was used for the computations.

The exhaust gas from combustion engines – such as the engines in cruise ships – contains a mixture of nitrogen oxides (NO_X). NO_X is the sum of NO and NO₂. In terms of health effects and limit values, NO₂ is the substance of interest.

When evaluating concentrations of NO₂ it is important to be aware that there is not a one-to-one correspondence between NO_X and NO₂; close to sources of pollution, concentrations of NO_X can be much higher than those of NO₂.

It is also important to note that the amount of available ozone in the background air sets a "ceiling", limiting the amount of NO_X that can be converted to NO₂ (the concept of a "ceiling" set by ozone applies for dispersion at a local scale, not for long-range transport).

As a point of reference a "Basic Run" was carried out, based on one specific set of input data. This Basic Run is discussed in details in the report; it yields a good impression of the contribution of pollution from cruise ships. Additional model runs were conducted to investigate the sensitivity of results to various assumptions. The following issues were explored:

Assumptions concerning the rate of direct emission of NO₂ (as a fraction of the NO_X emission);
Assumptions concerning background concentrations;
The effect of choosing a different year for meteorological data and background data;
Sensitivity to the spatial resolution of the calculations;
The effect of a time shift of emission data in respect to meteorological data;
The effect of receptor height;
The effect of the temperature of the exhaust gas from the stacks.

In relation to nitrogen oxides, an EU directive (99/30/EC) sets a limit for NO₂ that is based on hourly concentrations. The hourly concentration of NO₂ is allowed to exceed a limit of 200 μg/m³ no more than 18 times a year (this limit must be complied with in 2010).

Another limit value for NO₂ refers to the annual average, which must not exceed 40 μg/m³ (from 2010).

Some main results from the Basic Run are presented in Figur 2. These results can be compared to the first limit value mentioned above. The map shows the 19th highest NO₂ concentration during one year concentrations, resulting from the combined effect of cruise ships and the urban background pollution in the city of Copenhagen. The background pollution is assumed constant throughout the area. The values in Figur 2 are all in the interval between 98 and 101 μg/m³; according to the limit they are required to be less than 200 μg/m³. If the cruise ships had not been present, Figur 2 would have shown a constant value of 98 μg/m³, corresponding to the contribution from the urban background pollution.

Concerning the annual average concentration of NO₂, the Basic Run results in a level of around 23 μg/m³, almost unaffected by the presence of cruise ships. Their maximum contribution is 0.8 μg/m³ at the location where the impact is greatest. These numbers should be compared to a limit value of 40 μg/m³.

Klik her for at se figuren.

Figur 2 The left panel shows a map, while the right shows a corresponding schematic "map" of concentrations. The two maps cover the same area (1800 m x 4800 m). Each of the small sqares on the right is 200 x 200 m.The white rings on the schematic map represent quays. For each calculation point (receptor) the schematic map shows the nineteenth highest hourly concentration of NO₂ during one year, according to the Basic Run. The values displayed should be compared to the limit value of 200 μg/m³. Please note that the scale is limited to the interval 98 to 101 μg/m³. Throughout the black area there is a constant value of 98 μg/m³, and this value remains 98, irrespective of whether the cruise ships are present or not.

A series of additional model runs have been conducted in order to investigate the effects of different assumptions in various respects. These analyses do not change the overall conclusions derived from the Basis Run: That the increase of NO₂ concentrations resulting from the presence of cruise ships is not by any means capable of increasing the level of NO₂ above the limit values, neither close to the ships nor far away from them.

The discussion above concerns nitrogen oxides. In addition to these calculations, contributions of SO₂ and PM₁₀ from the cruise ships have been evaluated. The computations reveal that the contribution to SO₂ concentrations is much larger than estimated in the previous study, but that concentration levels are far from alarming. For particles in terms of PM₁₀, the contribution from cruise ships is very small compared to EU limit values.

In summary, the present study provides an answer to many questions concerning pollution from cruise ships in harbour, most notably the following:

Is the emission from cruise ships capable of increasing the 19th highest concentration value of NO₂? The answer is Yes, but only very little, and only in the immediate vicinity of the quays.
Is the presence of cruise ships capable of increasing the 19th highest concentration above the level defined by the limit value? The answer is a clear No.
Is the contribution from cruise ships to NO₂ pollution in terms of annual averages important? The answer is No.