I usually enjoy reading the articles in the significance magazine published by the RSS. Not only is it a glossy magazine (quite uncommon for statistics as a discipline) but also does it often feature very nice case studies from real life problems that matter.
Not so for the article in the current issue (December 2015) on the so called “Diesel Gate”. But before we look deeper into the problem let’s start with looking at emission regulations in the US and Europe. The following figure from “The Long Tail Pipe” illustrates the problem
Whereas the US restricts NOx very strongly, the EU pushes on COx. This makes one think as all emissions are bad for the environment and should equally regarded as “bad” no matter which side of the Atlantic you are residing. Not so! US car makers and consumers value big cars with big (gasoline) engines to reach their speed limit of 55mph as fast as possible and burn as much gas as possible in stop and go traffic – as gasoline in the US is comparably very cheap. As these big engines produce much COx, and (being a gasoline engine) very few NOx, the US limits are set accordingly and as a nice side effect protect the US car market towards more efficient and smaller Diesel engines from the EU and Japan.
But back to the Significance article. It looks into 5 “studies” from the NYT, Vox, Mother Jones and Associate Press, which all try to estimates the number of “Total US deaths” caused by Volkswagen’s defeat device in cars sold between 2009 and 2014 based on the estimated “Excess NOx”. As this estimated varies average miles per year driven and NOx death rates, the authors end up with this histogram of 27 different estimates on extra US NOx deaths
with an average of 160 resp. a median of roughly 80 “extra deaths”. Although it was hard to find a figure for the total annual US NOx emissions, I found a figure of 6,300,000 tons in 2004. With a best case death rate related to NOx of 0.00085 we get roughly 32,130 deaths from which up to 200 (or 0.0062%) are attributed to VWs defeat device. (The number goes down to 0.00056% with a death rate of 0.0095).
If we have a NOx problem in the US, VW probably did not contribute to it significantly with their defeat device.
Btw., the US count roughly 10,000 firearm-related homicides per year, for the period of 2009 to 2014 we face roughly twice as many deaths related to firearm misuse as we get from NOx pollution …