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Pollution from ships vs cars

Alasdair Anderson
In a recent article (E&T Feb - Hybrid Ships - https://eandt.theiet.org/content/articles/2019/01/hybrid-ships-take-to-the-high-seas/) it is stated that "According to figures originally published in the Guardian in 2009, one giant container ship can emit almost the same amount of cancer- and asthma-causing chemicals as 50 million cars, and around 50,000 premature deaths in Europe have been attributed to international shipping".  This seems a bit much to me, since there are only about 30 million cars in the whole of the UK. Can one container ship with say two diesel engines of 40,000 hp each produce the equivalent pollutants of the exhausts of 50 million cars with a combined engine power of perhaps around 2.5 billion hp? (Note that I am ignoring issues such as the 15,000-20,000 lorries kept off the road). As this information was originally published in the Guardian, does anyone know how the journalists gather and, more importantly, validate their statements?

Alasdair
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    There are no assumptions stated in the E&T article, presumably because there are no assumptions stated by the Guardian in the original article being quoted. Please note the reference is to cancer- and asthma-causing chemicals so it is not the CO2 that is in question. It is probably the NOX and similar compounds. If we assume that NOX is absent from petrol (spark ignition) engines but a product of diesel (compression ignition) engines then I guess only counting the diesel cars is valid. The figures show that 40% of the cars in the UK are diesel so that would mean out of 50 million cars, 20 million would be diesel.

    The lifespan of a ship is 25 years - it is unusual for a ship to be economically viable beyond its fifth special survey (every five years) due to the cost of rectifying the maintenance and corrosions issues to ensure another five years of life, though some only last 20 years.

    If you want the fuel consumption of one of these container ships I reckon you would be looking at around 1000 tonnes per day while at sea (call it a million litres). This would equate to one million cars driving around ten miles each (or to take the number of diesel cars mentioned above, 20 million diesel cars driving around half a mile each - an annual mileage of less than 200 miles).

    Even if you work on the total lifetime emissions you are not going to alter this significantly to get it anywhere near the normal annual mileage. Perhaps you can see why I am struggling to accept the comparison.

    Alasdair
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    There are no assumptions stated in the E&T article, presumably because there are no assumptions stated by the Guardian in the original article being quoted. Please note the reference is to cancer- and asthma-causing chemicals so it is not the CO2 that is in question. It is probably the NOX and similar compounds. If we assume that NOX is absent from petrol (spark ignition) engines but a product of diesel (compression ignition) engines then I guess only counting the diesel cars is valid. The figures show that 40% of the cars in the UK are diesel so that would mean out of 50 million cars, 20 million would be diesel.

    The lifespan of a ship is 25 years - it is unusual for a ship to be economically viable beyond its fifth special survey (every five years) due to the cost of rectifying the maintenance and corrosions issues to ensure another five years of life, though some only last 20 years.

    If you want the fuel consumption of one of these container ships I reckon you would be looking at around 1000 tonnes per day while at sea (call it a million litres). This would equate to one million cars driving around ten miles each (or to take the number of diesel cars mentioned above, 20 million diesel cars driving around half a mile each - an annual mileage of less than 200 miles).

    Even if you work on the total lifetime emissions you are not going to alter this significantly to get it anywhere near the normal annual mileage. Perhaps you can see why I am struggling to accept the comparison.

    Alasdair
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