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According to an article on CBC:

The report says that a mid-sized cruise ship can use as much as 150 tonnes of fuel each day, which emits as much particulate as one million cars. Is that right?

That's correct. And the reason for this is that their engines run 24/7. Even if they're in the ports, they have to keep running their engines, because it's not only a transport mode, it's a hotel facility. They have a spa on board, restaurants ... and that needs a lot of energy — more or less the same energy a mid-sized city needs.

Is the above factoid true?

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    Particulate emissions depend not only on the amount of fuels, but the type of fuel and the design of the engine. Ships often use dirtier fuel and can have weaker emission standards than cars – Henry Jul 23 '18 at 21:10
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    Note that the claim may for the average car, rather than cars running all day. – user43646 Jul 23 '18 at 22:11
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    This claim does seem really ambiguous. It may end up being one of the cases where there almost necessarily exists an interpretation of it in which it's true due to the multitude of different ways in which it could be interpreted. – Nat Jul 24 '18 at 3:19
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    how far are these cars driving? what speed at they travelling at? what size of engine and what is it's efficiency? My car sits in the garage 5 days a week, so any cruise ship is producing infinitely more emissions than my car on those days. – HorusKol Jul 24 '18 at 6:44
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    @blacksmith37 - The article and the underlying report are clearly talking about particulates, not CO2. – David Hammen Jul 24 '18 at 20:23
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Taking a "tonne" as being a metric ton, 150 tonnes is 150 Mg, or 150 million grams. So for this to be a true, a car would have to burn 150g/day.

http://www.autonews.com/article/20150325/OEM06/150329911/average-u.s.-gasoline-usage-lowest-in-3-decades-study-says

Gallons used per vehicle (524) dipped 14 percent from 2003, which was its maximum consumption year.

https://en.wikipedia.org/wiki/Gasoline#Density

The density of gasoline ranges from 0.71–0.77 kg/L

524 gallons is 1983 liters, giving 1407 kg/year, or 3.857 kg. Thus, if a cruise ship burns 150 tonnes a day, it burns as much as fuel as 38k cars. Only if a cruise ship produces 26 times as much particulates per kg fuel would this make sense.

Also, the claim "more or less the same energy a mid-sized city needs." is quite questionable. If we says that a "mid-sized" cruise ship has 3k passengers, and a "mid-sized" city has 100k population, then this would mean that a cruise ship is providing 33 times as much energy per person as a city. While it makes sense that it would be higher for a cruise ship, 33 times sounds rather high.

There is this, however:

Large ships run on heavy fuel oil, which is legally permitted to contain 3.5% sulphur – that’s 3,500 times what is permitted in road fuel. In EU ports and waters, ships are legally required to switch to a cleaner diesel, but even this, capped at 0.1% sulphur, is allowed to contain up to 100 times more sulphur than road fuel.

So, it appears that are particular types of particulates for which a cruise ship produces as much as one million cars, but the article is poorly worded in implying it is the amount of fuel, and the constant running of engines, rather than the different fuel composition, that causes it. Note also that if cruise ships were not burning this heavy fuel oil, then either it would be burned somewhere else, or not use at all, and the latter would be rather unlikely.

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    You didn't include the particulates coming out of that pipe on the bottom of the boat. – Daniel R Hicks Jul 24 '18 at 1:17
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    or particulate left behind on the road surface due to tyre wear – jwenting Jul 24 '18 at 7:15
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    Did you just calculated consume per day for the ship and per year for the car and compared both? – jean Jul 24 '18 at 11:19
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    @DanielRHicks Your comment makes no sense. – Acccumulation Jul 24 '18 at 14:47
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    @Acccumulation - Did you read the linked article? It says right up front that "a German environmental organization says that in terms of environmental impact, the industry is an absolute nightmare." The CBC article is parroting a press release from nabu.de. – David Hammen Jul 24 '18 at 22:02

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