As air pollution spikes in Europe’s cities prompt car-free days and talk of banning diesel cars, it’s easy to forget the other culprits behind the air quality crisis: diesel machines. Known in legislation by the innocuous term ‘non-road mobile machinery’, their air pollutant emission limits are now finally under revision.The last directive dated back to 1997 and the new rules will set standards for decades to come. Air pollution is causing more than 450,000 premature deaths every year in Europe and a recent Eurobarometer survey confirmed that air pollution is now the biggest environmental concern of European citizens. Efficient regulation of emissions sources is therefore key to mitigating the exposure of citizens to air pollution.