Carbon dioxide emissions from mobile air conditioning units may be six times higher than originally feared according to a new study.
Researchers at Empa in Switzerland looked into the impact of mobile air conditioning on fuel consumption and pollutant emissions of diesel cars and confirmed that they remain running at ambient temperatures below the desired temperature of the passenger compartment unless they are manually switched off. Their model, used to calculate extra emissions and fuel consumption, found that when applied to a central European region and compared with the US EPA MOBILE6 model, the Empa model averaged annual CO2 output six times higher.
A paper published in Environmental Science & Technology outlines that up to two thirds of these emissions are caused by operating at temperatures below 188C where mere ventilation is sufficient.
MOBILE6 is applied all over the world and is based only on measurements above 228C assuming that the air conditioning units do not run at lower temperatures. However, the systems in European cars, if left switched on, keep running except below 58C to prevent freezing.
The authors suggest that the public needs to be educated on this matter and discussions should be set up with manufacturers to ensure air conditioning units turn off completely if no cooling is needed and turn on only when the windscreen mists.
