"Cleaner" should not, however, be confused with clean. An Australian study of real-life emissions from woodheaters satisfying the current Australian standard, found that particle emissions averaged 9.4 g/kg wood burned (range 2.6 to 21.7). A heater with average wood consumption of 4 tonnes per year therefore emits 37.6 kg of PM2.5, i.e. particles less than 2.5 micrometers. This can be compared with a passenger car satisfying the current Euro 5 standards (introduced September 2009) of 0.005 g/km. So one new wood heater emits as much PM2.5 per year as 367 passenger cars each driving 20,000 km a year. A recent European study identified PM2.5 as the most health-hazardous air pollutant, causing an estimated 492,000 premature deaths. The next worst pollutant, ozone, is responsible for 21,000 premature deaths.