Air pollution on cruise ship decks may be as bad as in cities like Beijing and Santiago, Chile, according to a new study from researchers at Johns Hopkins University.

The study measured pollution levels on the decks of four cruise ships — Carnival Liberty, Carnival Freedom, Holland America MS Amsterdam, and Emerald Princess — in front of and behind the ship's smokestacks.

The researchers found that concentrations of particulate matter pollution on the decks of the observed ships was similar to levels found in Beijing, Santiago, and Antwerp, Belgium.

Air pollution on cruise ship decks may be as bad as in cities like Beijing and Santiago, Chile, according to a new study from researchers at Johns Hopkins University.

The study measured pollution levels on the decks of four cruise ships — Carnival Liberty, Carnival Freedom, Holland America MS Amsterdam, and Emerald Princess — in front of and behind the ship's smokestacks. The researchers found that concentrations of particulate matter pollution on the decks of the observed ships was similar to levels found in Beijing, Santiago, and Antwerp, Belgium. (The study defines particular matter pollution as "small solids or liquid droplets suspended in the air.") Pollution behind the smokestacks, including in areas intended for exercises like basketball courts and running tracks, was much worse than in front of the smokestacks, according to the study.

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Of the ships monitored in the study, Emerald Princess was found to have the highest average concentration of particulate matter pollution both in front of and behind its smokestacks.

Particulate matter pollution can harm the heart and lungs, especially particles that measure less than 10 micrometers in diameter, since they can travel further into the lungs. Most of the particulate matter pollution in ship exhaust measures less than one micrometer in diameter, which can make people more vulnerable to contracting atherosclerosis and developing more severe asthma, the study said.

Have you worked on a cruise ship? Do you have a story to share? Email this reporter at mmatousek@businessinsider.com.