The difficulty of calculating deaths caused by the Volkswagen scandal

Scandal over cheating emissions tests led many to wonder how many deaths may have been caused, but such calculations are riddled with uncertainties

In September 2015, the US Environmental Protection Agency revealed that Volkswagen and Audi diesel vehicles sold between 2009 and 2015 were emitting up to 40 times the official limit of nitrogen oxides (NOx). It said the vehicles had been fitted with "defeat devices" that lowered NOx outputs to meet standards only during emissions testing, which meant affected vehicles may have been contributing excess NOx to the atmosphere for up to seven years.

Through chemical reactions with other ambient pollutants, NOx can form pollutants that are harmful to health, including nitrogen dioxide, ozone, and particles such as ammonium nitrate that contribute to particulate matter (PM) air pollution. The excess NOx pollution attributable to the defeat devices is likely to have led to increased ambient pollution, which subsequently may have affected human health.