Study leader Roya Bahreini of the Cooperative Institute for Research in Environmental Sciences at the National Oceanic and Atmospheric Administration's Earth System Research Laboratory and colleagues said secondary organic aerosols are tiny particles that make up 40 percent to 60 percent of the aerosol mass in urban environments, which can cause heart or respiratory problems.
"The surprising result we found was that it wasn't diesel engines that were contributing the most to the organic aerosols in Los Angeles," Bahreini said in a statement. "This was contrary to what the scientific community expected."
In Los Angeles, the scientists made three weekday and three weekend flights with the NOAA P3 research aircraft to measure different aspects of air pollution.
Diesel trucks were used less during weekends, but gasoline vehicles remained nearly constant throughout the week. The researchers expected weekend levels of secondary organic aerosols would take a dive from their weekday level, but it did not.
Instead the levels of the secondary organic aerosol particles remained relatively unchanged from their weekday levels, Bahreini said.
"The contribution of diesel to secondary organic aerosols is almost negligible," Bahreini said. "Even being conservative, we could deduce from our results that the maximum upper limit of contribution to secondary organic aerosols would be 20 percent."
The findings were published in Geophysical Research Letters.