Exhaust gas that they produce smaller quantities of toxic pollutants (e.g. oxides of nitrogen) than petrol and diesel engines of the same power. They produce larger quantities of carbon dioxide but less carbon monoxide due to more efficient combustion. Researchers from the University of California, Los Angeles School of Public Health say preliminary results of their statistical study of children listed in the California Cancer Registry born between 1998 and 2007 found that traffic pollution may be associated with a 5% to 15% increase in the likelihood of some cancers. A World Health Organization study found that diesel fumes cause an increase
Exhaust gas the European Union's man-made CO emissions, with passenger cars contributing about 12%. European emission standards limit the CO emissions of new passenger cars and light vehicles. The European Union average new car CO emissions figure dropped by 5.4% in the year to the first quarter of 2010, down to 145.6 g/km. Vehicle exhaust contains much water vapour. There has been research into ways that troops in deserts can recover drinkable water from their vehicles' exhaust gases. Emission standards focus on reducing pollutants contained in the exhaust gases from vehicles as well as from industrial flue gas stacks and other air