Shipborne observations of air pollutants over the Western Mediterranean
The warm and sunny climate as well as the sea breeze typical of the summer weather along the coasts favours the formation of ‘smog’ with high concentrations of ozone and other air pollutants in the Western Mediterranean. Measurements of air pollutants in the Mediterranean Basin on monitoring stations and during short term campaigns have shown high levels of ozone as well as particulate matter. The sources appear to be local as well as long range transport. However large parts of the area is not covered by monitoring stations and there is in particular a lack of observations over the sea.
In order to fill this gap and provide data that allow learning about sources of air pollutants and transformation processes, the JRC has initiated a long-term monitoring program in collaboration with the Italian cruise line Costa Crociere. Measurements have been performed regularly during spring-summer-autumn since 2006 from a monitoring station placed on Costa Crociere cruise ships following a fixed weekly route in the Western Mediterranean.
This long-term measurement activity provides a unique data set, useful for answering questions like:
concentration levels of the most important air pollutants?
main sources (local vs. long range transport)?
trends in concentrations?
Do atmospheric chemical transport models give an adequate simulation of the real situation?
What is measured and why?
High levels of ozone and particulate matter cause risks to human health in many parts of the Mediterranean areas. Ozone causes also damage to vegetation.
Besides the long-lived greenhouse gases such as carbon dioxide, methane and nitrous oxide also short-lived air pollutants such as ozone in the lower atmosphere and light-absorbing particles (so-called Black Carbon) are important man-made atmospheric components influencing the absorption of radiation in the atmosphere.
On this background it was decided to measure ozone, Black Carbon (BC) and other particulate matter together with gases that are involved in the formation of ozone or particles in the atmosphere (NOx, SO2, carbon monoxide).
Distribution of air pollutants in the Western Mediterranean
The measurements show the distribution of air pollutants along the route of the Costa Crociere ships in the Western Mediterranean. The influence of large urban centres like Marseille, Barcelona, Rome and Genova is often seen (the red ‘hot spots’ seen in the figure). An analysis of the measurements has also shown that the circulation of air caused by the sea breeze is an important reason for the high levels of ozone.
Impact of ship traffic on air pollution
Ship emissions have become increasingly important sources of air pollution in Europe as other sources are becoming tightly regulated (traffic, power plants,…..) while regulations on ship emissions have remained relatively lenient. Ships are particularly important sources of NOx, SO2 and consequently also of sulphate, formed by oxidation of SO2 in the atmosphere; it has been calculated that 54% of the total sulphate aerosol column burden over the Mediterranean in summer originates from ship emissions (Marmer and Langmann, 2005). However estimates of ship emissions are uncertain and need to be improved; the measurements on the Costa Crociere ships have been used.
An intense ship traffic, particularly of tank ships. is found along a route from the Strait of Gibraltar to the Suez Channel. The measurements show elevated levels of air pollutants in the vicinity of this route:
Route with intense ship traffic is marked by grey dots.
Sealittercam for monitoring of floating marine litter
In addition to the observations of air pollution, a new activity has been initiated at the Costa Crociere ships:
Floating marine litter has become a worldwide environmental problem causing increasing concern, however little quantitative information is available about the amounts and the distribution of this type of litter.
A novel optical system for automated observation of floating litter at the sea, the JRC Sealittercam, is now being tested on the Costa Crociere ships. The system is based on acquisition of high resolution pictures of the sea surface in from of the ship bow followed by image recognition analysis.
For the atmospheric measurements:
Jens Hjorth, phone +39.0332.789076, email:jens.hjorth at jrc.ec.europa.eu
For the Sealittercam:
Georg Hanke, phone +39.0332.785586, email:georg.hanke at jrc.ec.europa.eu