The exhaust fumes from gasoline vehicles contribute more to the production of a specific type of air pollution-secondary organic aerosols (SOA)-than those from diesel vehicles, according to a new study by scientists from the Cooperative Institute for Research in Environmental Sciences (CIRES). Secondary organic aerosols, tiny “tar balls” resulting from combustion products of internal combustion engines that can encapsulate gaseous pollutants, have been identified as a danger to health. Diesel fuel oil seems to be more responsible for these aerosols than gasoline which is counter to normal thinking on the subject.