An undercover investigation reveals air quality on a cruise ship deck could be worse than the world's most polluted cities

Following is a transcript of the video.

Thinking of going on a cruise for the fresh ocean air? Think again. A recent undercover investigation on P&O Cruises' ship Oceana revealed ultra-fine particles in the air emitted from burning fuel.

On deck, downwind of the smokestacks, the investigative team measured 84,000 particulates per cubic cm. Closer to the smokestacks, the numbers rocketed to 144,000.

Sometimes even peaking at 226,000. According to Dr. Matthew Loxham, a research fellow in respiratory biology and air pollution toxicology in University of Southampton, "These are levels that you would expect to see in the most polluted cities."

These pollutants can get lodged in the lungs. Over time, it can cause asthma and chronic lung disease. The risk for health problems is greatest among crew members but passengers should also be careful.

Each day, the average cruise ship produces as much air pollution as one million cars.

P&O Cruises is currently taking action. It says it's installing cleaning systems to reduce exhaust. It also reports that since 2005, it has reduced fuel consumption by 28%.

That's good news for future cruise passengers.

When asked for comment, P&O Cruises responded with the following.

"We continue to invest heavily in environmental technology for Oceana and for all ships across the fleet. In keeping with this environmental strategy, EGCS will be fitted on Oceana in dry dock later this year. These EGCS will significantly reduce sulphur oxides (SOX), soot and particulate matter … We are actively engaging scientists and independent third party groups to carry out similar studies using accredited equipment and methods and once complete we will share these results with the industry in order to understand and execute best practice."