The mayor of London’s proposed ultra-low emission zone, to come into effect from 8 April 2019 (Report, 24 October), risks perpetuating the problem. The discourse currently focuses on NOx emissions, specifically those from diesel engines, but this is hardly the only pollutant. By insisting on Euro 4 (2005) standards for petrol cars and the significantly cleaner Euro 6 (2014) standards for diesel, petrol cars in London will be able to emit double the carbon monoxide of diesels and particulate emissions from petrol vehicles will still be unregulated (whereas diesel will have strict limits). Given that PM2.5 levels are more than double the WHO limit in London (Report, 5 October), allowing petrol cars to continue to emit unlimited levels of particulates in London is mad.

Perverse government incentives, such as when there was a focus on CO 2 at the expense of other emissions from vehicles in the 2000s, are exactly what caused today’s situation. All vehicles, even electric ones, emit something – until we have legislation that applies to them all equally, we will just push the problem around. A start would be to insist on Euro 6 for all vehicles in London from 2019.

Dr Felix Leach

Research fellow and tutor in engineering science, Keble College, University of Oxford

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