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How much pollution has been saved by autocatalysts?

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Category: Emissions Control

Subject: How much pollution has been saved by autocatalysts?

Question

How many tonnes of pollutants have been prevented from reaching the atmosphere by automotive catalysts since they were first introduced in the 1970s?

Answer

There was a claim in Platinum 2004 that Johnson Matthey autocatalysts had already prevented 4.5 billion tonnes of pollutants from reaching the atmosphere. Johnson Matthey has since made another 250-300 million catalysts, and only claim to have made a third of the autocatalysts ever made, which suggests that the global total is significantly higher.

Working from first principles is difficult because there is little data readily available about catalyst systems and conversion rates from the earlier generations of vehicles. However, there is a chain of logic that justifies an estimate in the order of billions of tonnes:

  1. Focussing on gasoline (the most relevant technology for the historical markets and for the USA/Asia), typical pollution removal rates from two gasoline test cars over the European drive cycle are:

    1. A 2002 Ford Focus emits 7.90 g km–1 HC, CO  and NOx from the engine, Euro 3 regulations limit was combined 2.65 g km–1, therefore 5.25 g km–1 removed

    2. A current Audi A3 emits 5.62 g km–1 HC, CO  and NOx from the engine, Euro 6 regulations limit is combined 1.16 g km–1, therefore 4.46 g km–1 removed

    3. This suggests a representative pollutant removal rate for the last decade is 5 g km–1

  2. Assuming a lifetime of 160,000 km, each catalyst will remove 160,000 × 5 = 800,000 g = 0.8 tonnes of pollutants

  3. Johnson Matthey have made 750 million catalysts. At 0.8 tonnes each this equates to 600 million tonnes

  4. Johnson Matthey have made approximately 1/3 of the autocatalysts ever made, therefore the global total for all autocatalysts is 1.8 billion tonnes

  5. Some factors will have been significantly underestimated, as described below, so the true number is likely to be higher:

    1. 5 g km–1 is representative of a small/medium passenger car, rates will be higher for larger cars/engines

    2. 5 g km–1 is for a part meeting the full useful life emissions limit, for most of its life the catalyst will be less deactivated and deliver higher conversion rates

    3. The vast majority of catalysts/vehicles keep operating beyond the legislated full useful life, preventing further pollution from entering the atmosphere

    4. US cars from the early 1970s met targets of 30–40 g mile–1 through engine tuning. The first catalysts reduced this to 4 g mile–1. Even with a shorter lifetime of 50,000 miles this gives a higher lifetime removal rate of 1.8 tonnes per catalyst. Therefore many of the early catalysts will have removed more pollution than their modern counterparts

    5. However, factors a-d will be partially offset by the fact that the average number of catalysts per vehicle is greater than one

 Date Posted: 2nd October 2014 

 

Answered by: Dr Chris Morgan

Affiliation: Johnson Matthey Emission Control Technologies, Royston, UK