Dangerous cargo: air pollution in port cities

Many of the world’s biggest cities are ports, which presents a very particular set of air pollution issues. Ship fuel oil contains 3,500 times more sulfur than diesel — so while shipping accounts for only 2% of global carbon emissions, it produces 13% of sulfur emissions. Sulfur dioxide pollution can be a problem in busy waters, and onshore breezes bring sulfur oxides (SOx) into coastal cities.

For this reason, burning high sulfur fuel has been banned in the Baltic since 2015. To enforce compliance, sniffer drones — described as “breathalyzers for ships” — have been developed to inspect ships on the move. Results have been impressive: an 88% reduction of SOx in the Baltic. Areas including the North Sea and Mediterranean have followed suit and seen similar improvements.

New problems arise once a ship has docked and switched to auxiliary power. “These generators are usually diesel, and run all the time the ship is in harbour,” says Emre Aydin, senior air quality consultant at WSP in Gothenburg, Sweden. “Cruise ports such as Venice have recorded very high nitrogen oxide and particulate readings largely because of this.”

One alternative is to crane onto the ship a container-sized generator powered by liquid natural gas. A better solution is onshore power supply (OPS), though this presents difficulties of its own. “Connecting a ship to the grid solves the problem, but this can be challenging to organize,” says Aydin. Ships consume huge amounts of electricity — a 5,000-passenger cruise liner can require several megawatts — which involves both high-voltage cabling infrastructure onshore, and equipping ships to connect to it. Scandinavian ferry operator Stena Line was an early adopter of OPS, and has now gone a step further, using OPS at Oslo to charge its latest model of hybrid-electric ships.

Not all air pollution at ports comes from ships. A concentration of HGVs, locomotives and processing industries means that good housekeeping is essential to protect local people from high pollution levels. “Port authorities need to work closely with meteorologists to minimize impacts,” says Aydin. “For example, dry weather and wind makes dust from the unloading of raw materials like coal or sand a major source of particulates. Commercially it is not usually practicable to wait until the wind changes, but you can deploy sprinkler systems and road sweepers to keep dust levels to a minimum.”

This article appeared in The Possible issue 05, as part of a longer feature on improving air quality in cities