photo by Dale Frost, courtesy the Port of San Diego
I have never taken to the high seas on a cruise ship, but when I imagine such a vacation, I assume it would involve plenty of fresh air. I also assume this assumption is pretty common.
Unfortunately for me, and more unfortunately for actual passengers and crew, a new study indicates that my assumption may not hold water.
The Miami Herald recently reported that an associate professor at the Johns Hopkins Bloomberg School of Public Health has published the results of a study in which he secretly measured levels of particulate matter in the air on four cruise ships. The professor, Ryan Kennedy, found that these levels were comparable to highly polluted urban areas such as Beijing.
Carnival Corporation, which operates two of the four ships Kennedy tested, said that the results were “completely ridiculous, inaccurate and in no way represent reality,” the Herald reported.
The Environmental Protection Agency currently does not have standards defining the safe limits of the ultrafine particles Kennedy measured, although the agency is reviewing data on the subject. Kennedy, however, observed that many passengers are under the mistaken impression that air pollution caused by ships is effectively dispersed in the open ocean. His results undermine this idea.
Ultrafine particles, sometimes called nanoparticles, are small enough that they can enter the bloodstream when inhaled, which makes them a health concern, especially for the very old and the very young. Naresh Kumar, an associate professor of environmental health in the department of public health sciences at the University of Miami, told the Miami Herald that the levels Kennedy measured “should be a matter of concern.”
Not surprisingly, the researcher found that when the ship was in motion away from port, particulates from smokestack emissions tended to be higher in the stern (the rear) of the ship than in the front. That makes sense: If the ship is moving forward at cruising speed, and assuming no strong winds are blowing from behind, then smokestack emissions will tend to fall over the decks that are aft of the stacks.
Kennedy’s study is only one of a handful measuring air quality aboard cruise ships at sea and, as critics have pointed out, his study was not published in a peer-reviewed journal. But the effect of shipping, including cruise ships, on the air quality of ports has been a well-document concern for quite some time. Several years ago, I noted that mandates for cleaner fuel would translate into a cleaner balcony at my Fort Lauderdale, Florida apartment. In my actual experience, my balcony really does stay cleaner than it used to, or at least it doesn’t get sooty quite as fast.
The EPA phased in stricter standards for the sulfur content in diesel fuels as of 2012, and ships passing within 200 nautical miles of the American or Canadian coastline have been held to standards of no more than 1,000 parts per million since 2015. In North America, most ships must install “scrubbers” in order to burn heavy fuel oil, though California doesn’t allow scrubbers within 24 miles of its shores. The United Nations International Maritime Organization set a 2020 deadline for adoption of low-sulfur maritime fuels, which the IMO defined as 0.5 percent or less, regardless of where ships operate. Some analysts have observed that the IMO has no real means to enforce this standard, but all major global ports have committed to low-sulfur fuels in theory.
Air pollution from ships, including cruise ships, is not only a matter of sulfur content, however. Diesel fuel emissions routinely include sulfur dioxide, nitrogen oxide, hydrocarbons and particulates (a subset of which Kennedy measured in his study). Together, these emissions sometimes can create alarming health effects in people exposed to them or environmental problems such as acid rain – not to mention the soot and smog that port cities have long fought against. The IMO agreed in 2018 that participating countries would try to reduce overall carbon emissions from ships by at least half by 2050. The New York Times reported that some ship operators, including cruise ship companies, are building ships that can run on cleaner liquefied natural gas, suggesting one potential avenue for progress.
There is plenty of cruise ship traffic through Port Everglades, which is just a few miles from my home, and a huge amount of construction in downtown Fort Lauderdale. This means there is still a good bit of matter in the air of my hometown, even with improved marine fuel standards. But I never imagined I would have to think about ways to keep particulates out of my lungs in the unlikely event I ever take a vacation cruise. For the record, I have nothing against cruises; I know many people love them. I just have other ways I prefer to travel on my time away from work.
Cruise passengers and crew, especially those whose age or health might make them particularly susceptible, ought to be made aware of any heightened air pollution exposure in the areas they frequent. Ships themselves could be equipped with monitors, so those in command can try to take mitigating actions when pollution levels are high. The ships also could be designed to direct more strenuous physical activities to parts of the vessel where particulate levels tend to be lower.
I have nothing against cruise ships or the internal combustion engine. They both serve useful purposes, but they each have trade-offs that involve costs as well as benefits. If exposure to particulates and other pollutants is a health “cost” incurred by passengers, then reducing such exposure represents a better bargain for cruise customers. Who wouldn’t want to sign up for that?